QUESTIONS

Panel 1 shows carbon skeletons of chains, branched trees, and rings. An introductory text reads, carbon has a unique role in the cell because of its ability to form strong covalent bonds with other carbon atoms. Thus carbon atoms can join to form chains, branched trees, and rings as follows:

Chains are shown as an 8-carbon linear chain in which each carbon atom has two open single bonds except for the two terminal atoms, which each have three open single bonds. Chains can also be written as a triangular waveform.

Branched trees are shown as a 2-carbon linear chain in which each carbon atom is bonded to two other carbon atoms, each of which are attached to three open single bonds. The two carbon atoms in the linear chain are also attached to an open single bond. This can also be written as a horizontal line that has a V-shaped branch attached on both ends.

Rings are shown as two 6-carbon rings that are bound to each other. These two rings share two carbon atoms at the fusion site. The other carbon atoms each have two open single bonds attached to them. This can also be written as two fused hexagonal rings.

Panel 2 shows covalent bond types. An introductory text reads, a covalent bond forms when two atoms come very close together and share one or more of their outer-shell electrons. Each atom forms a fixed number of covalent bonds in a defined spatial arrangement.

In single bonds, two electrons are shared per bond. Ball and stick models of carbon with 4 single bonds, nitrogen with 3 single bonds, and oxygen with two single bonds are shown.

In double bonds, four electrons are shared per bond. Ball and stick models of carbon with two single bonds and a double bond, nitrogen with a single bond and a double bond, and oxygen with a double bond are shown.

Accompanying text reads, the precise spatial arrangement of covalent bonds influences the three-dimensional structure and chemistry of molecules. A red colored text reads, in this review panel, we see how covalent bonds are used in a variety of biological molecules.

Panel 5 shows compounds in which carbon is covalently bound to an oxygen. An introductory text reads, many biological compounds contain a carbon covalently bonded to an oxygen. For example,

Alcohol: A structure shows a central carbon atom single bonded to two hydrogen atoms and O H. A text beside reads, O H is called a hydroxyl group.

Aldehyde: A structure shows a central carbon atom single bonded a hydrogen atom and double bonded to an oxygen atom.

Ketone: A central carbon atom is double bonded to an oxygen and single bonded to two carbon atoms. The two carbon atoms have three more single bonds.

A text beside aldehyde and ketone reads, the C double bond O is called a carbonyl group.

Carboxylic acid: A central carbon atom is single bonded to O H and double bonded to an oxygen atom. A text beside reads, C O O H is called carboxyl group. In water, this loses an H superscript plus ion to become C O O superscript minus.

Esters: Esters are formed by combining an acid and an alcohol. A chemical reaction below shows an acid and an alcohol reacting to yield an ester and a water molecule. In acid, a central carbon atom is double bonded to an oxygen atom and single bonded to a carbon atom and O H. The carbon atom has three single bonds. In alcohol, a carbon atom is single bonded O H and has three single bonds. In ester, a central carbon atom is double bonded to an oxygen atom and single bonded to a carbon atom and an oxygen atom which is single bonded to a carbon atom. The carbon atoms have three single bonds.

Text below reads, amides are formed by combining an acid and an amine. Unlike amines, amides are uncharged in water. An example is the peptide bond that joins amino acids in a protein.

A chemical reaction is shown in which an acid reacts with an amine to form an amide and H subscript 2 O. In the acid, a carbon atom is single bonded to O H and double bonded to O. In the amine, a central carbon is single bonded to H subscript 2 N. The carbon has three single bonds. In the amide, a central nitrogen atom is single bonded to two carbon atoms and a hydrogen atom. One carbon atom is double bonded to an oxygen atom and the other carbon atom has three single bonds.

A text beside reads, phosphate esters can form between a phosphate and a free hydroxyl group. Phosphate groups are often covalently attached to proteins in this way.

An equation below shows a carbon single bonded to a hydroxyl group reacting with inorganic phosphate to form a phosphate ester and H subscript 2 O. In phosphate ester, a central phosphorous atom is double bonded to an oxygen atom, single bonded to two negatively charged oxygen ions, and single bonded to an oxygen that is bound to carbon. Phosphate esters can also be represented as follows: A phosphorous atom single bonded to an oxygen atom which is single bonded to a carbon atom. The carbon atom has three open single bonds attached to it.

The next paragraph reads, the combination of a phosphate and a carboxyl group, or two or more phosphate groups, produces an acid anhydride. Because compounds of this type release a large amount of free energy when the bond is broken by hydrolysis in the cell, they are often said to contain a high-energy bond.

An equation shows a chemical reaction, in which a carboxyl group reacts with phosphoric acid to form carboxylic-phosphoric acid anhydride. This reaction is reversible; in the forward reaction a water molecule is released and in the reverse reaction a water molecule is added. Text reads, “high-energy” acyl phosphate bond (carboxylic-phosphoric acid anhydride) found in some metabolites. The structure can also be presented as follows: a central carbon atom with a single bonded oxygen, a double bonded oxygen, and an open single bond; the single bonded oxygen is further single bonded to a phosphate group.

Another equation shows a phosphoanhydride undergoing a reversible reaction with phosphoric acid to form a compound with two phosphate groups. Accompanying text reads, “high-energy” phosphoanhydride bond found in molecules such as A T P. This can be written as: an oxygen atom single bonded to a phosphate which is further single bonded to another phosphate.

Panel 1 shows examples of hydrogen bonds. The text reads, because they are polarized, two adjacent H subscript 2 O molecules can form a noncovalent linkage known as a hydrogen bond. Hydrogen bonds have only about 1/20 the strength of a covalent bond. Hydrogen bonds are strongest when the three atoms lie in a straight line.

An illustration beside depicts a ball and stick model of two water molecules that are linked by a hashed hydrogen bond.

A chemical structure beside the illustration is as follows: an oxygen atom is single bonded to two hydrogen atoms and hash bonded to a hydrogen atom of an O H group. The bond length of the hydrogen bond is 0.17 nanometers and the length of the covalent bond is 0.10 nanometers.

Panel 2 discusses the polarity of water molecules. The text reads, two atoms connected by a covalent bond may exert different attractions for the electrons of the bond. In such cases, the bond is polar, with one end slightly negatively charged, denoted delta superscript minus, and the other slightly positively charged, denoted delta superscript plus.

A ball and stick model is shown, in which an oxygen atom is single bonded to two hydrogen atoms. One hydrogen atom is above the oxygen atom and the other hydrogen atom is angled down to the right of oxygen atom. Two wave pulses originate from the oxygen atom and travels outward opposite the hydrogen atoms. The hydrogen atoms have partial positive charges and the end of the wave pulses correspond to partial negative charges. The region between the two hydrogen atoms is labeled electropositive region and the region with the wave pulses is labeled electronegative region.

The text below reads, although a water molecule has an overall neutral charge, meaning it has the same number of electrons and protons, the electrons are asymmetrically distributed, making the molecule polar. The oxygen nucleus draws electrons away from the hydrogen nuclei, leaving the hydrogen nuclei with a small net positive charge. The excess of electron density on the oxygen atom creates weakly negative regions at the other two corners of an imaginary tetrahedron. A red colored text reads, on these pages, we review the chemical properties of water and see how water influences the behavior of biological molecules.

Panel 4 describes hydrophilic molecules. The text reads, substances that dissolve readily in water are termed hydrophilic. They include ions and polar molecules that attract water molecules through electrical charge effects. Water molecules surround each ion or polar molecule and carry it into solution.

An illustration shows the structure of N a plus ion and C l minus ion. The structure of N a plus depicts N a superscript plus atom at the center surrounded by five water molecules in which the negatively charged oxygen ions are attracted toward the center. The structure of C l minus ion depicts C l superscript minus atom at the center surrounded by five water molecules in which positively charged hydrogen ions are attracted toward the center. In a water molecule, an oxygen atom is single bonded to two hydrogen atoms.

The text below reads, ionic substances such as sodium chloride dissolve because water molecules are attracted to the positive, N a plus, or negative, C l minus, charge of each ion.

Another illustration beside depicts the chemical structure of urea in which a central carbon atom is single bonded to two nitrogen atoms and double bonded to an oxygen atom. The nitrogen atoms are single bonded to two hydrogen atoms. Five water molecules are hydrogen bonded to the urea structure.

A text below reads, polar substances such as urea dissolve because their molecules form hydrogen bonds with the surrounding water molecules.

Panel 6 discusses water as a solvent. The text reads, many substances, such as household sugar, or sucrose, dissolve in water. That is, their molecules separate from each other, each becoming surrounded by water molecules.

An illustration shows a beaker containing water with a sugar crystal suspended in it. As the sugar dissolves the beaker contains many smaller sugar molecules.

Text beside the illustration reads, when a substance dissolves in a liquid, the mixture is termed a solution. The dissolved substance, in this case sugar, is the solute, and the liquid that does the dissolving, in this case water, is the solvent. Water is an excellent solvent for hydrophilic substances because of its polar bonds.

Panel 7 describes acids. The text reads, substances that release hydrogen ions, or protons, into solution are called acids.

A chemical reaction is shown in which hydrochloric acid, which is a strong acid, dissociates to form a hydrogen ion and a chloride ion.

The text below reads, many of the acids important in the cell are not completely dissociated, and they are therefore weak acids--for example, the carboxyl group, written as hyphen C O O H, which dissociates to give a hydrogen ion in solution.

A chemical reaction is shown, in which a carboxyl group, which is a weak acid, dissociates to form a hydrogen ion and a carbon single bonded to a negatively charged oxygen ion and double bonded to an oxygen atom. This reaction is reversible.

Panel 8 describes hydrogen ion exchange. The text reads, positively charged hydrogen ions, written as H plus, can spontaneously move from one water molecule to another, thereby creating two ionic species.

A chemical reaction is shown, in which two hydrogen bonded water molecules undergo a reversible reaction to yield a hydronium ion and a hydroxyl ion. In the hydronium ion, a positively charged central oxygen ion is single bonded to three hydrogen atoms. In the hydroxyl ion, a negatively charged oxygen ion is single bonded to a hydrogen atom.

It is noted that the reaction is often written as H subscript 2 O undergoes a reversible reaction to yield H plus and O H minus.

The text at the bottom reads, because the process is rapidly reversible, hydrogen ions are continually shuttling between water molecules. Pure water contains equal concentrations of hydronium ions and hydroxyl ions, both at 10 superscript negative 7 moles.

Panel 9 reviews P H. The text reads, the acidity of a solution is defined by the concentration of hydronium ions, written as H subscript 3 O superscript plus, it possesses, generally abbreviated as H plus. For convenience, we use the P H scale, where P H equals minus log of concentration of H plus ion to the base 10.

For pure water concentration of H plus ion equals 10 to the negative seventh power moles per liter. The P H of pure water equals 7.0.

A chart beside depicts the H plus concentration in moles per liter for acidic and basic solutions. The data are as follows:

Acidic P H values are from P H 0 to P H 6. At P H 0 the concentration of H plus equals 1 mole per liter. At P H 1 the concentration of H plus equals 10 to the negative first power moles per liter. At P H 2 the concentration of H plus equals 10 to the negative second power moles per liter. At P H 3 the concentration of H plus equals 10 to the negative third power moles per liter. At P H 4 the concentration of H plus equals 10 the negative fourth power moles per liter. At P H 5 the concentration of H plus equals 10 to the negative fifth power moles per liter. At P H 6 the concentration of H plus equals 10 to the negative sixth power moles per liter.

Neutral P H occurs at P H 7. At P H 7 the concentration of H plus equals 10 to the negative seventh power moles per liter. Pure water has a P H of 7.

Basic P H values are from P H 8 to P H 14. At P H 8 the concentration of H plus equals 10 to the negative eighth power moles per liter. At P H 9 the concentration of H plus equals 10 to the negative ninth power moles per liter. At P H 10 the concentration of H plus equals 10 to the negative tenth power moles per liter. At P H 11 the concentration of H plus equals 10 to the negative eleventh power moles per liter. At P H 12 the concentration of H plus equals 10 to the negative twelfth power moles per liter. At P H 13 the concentration of H plus equals 10 to the negative thirteenth power moles per liter. At P H 14 the concentration of H plus equals 10 to the negative fourteenth power moles per liter.

Panel 1 provides an overview of weak noncovalent chemical bonds. The text reads, organic molecules can interact with other molecules through three types of short-range attractive forces known as noncovalent bonds: van der Waals attractions, electrostatic attractions, and hydrogen bonds. The repulsion of hydrophobic groups from water is also important for these interactions and for the folding of biological macromolecules.

An illustration depicts two protein structures whose surfaces are joined by weak noncovalent bonds.

The text below reads, weak noncovalent bonds have less than 1/20 the strength of a strong covalent bond. They are strong enough to provide tight binding only when many of them are formed simultaneously.

Panel 2 describes van der Waals attractions. The text reads, if two atoms are too close together, they repel each other very strongly. For this reason, an atom can often be treated as a sphere with a fixed radius. The characteristic size for each atom is specified by a unique van der Waals radius. The contact distance between any two noncovalently bonded atoms is the sum of their van der Waals radii.

Four sphere ball models represent different atoms as follows: A hydrogen atom is represented by a gray sphere with a 0.12 nanometer radius. A carbon atom is represented by a black sphere with a 0.2 nanometer radius. A nitrogen atom is represented by a blue sphere with a 0.15 nanometer radius. An oxygen atom is represented by a red sphere with a 0.14 nanometer radius.

The text below reads, at very short distances, any two atoms show a weak bonding interaction due to their fluctuating electrical charges. The two atoms will be attracted to each other in this way until the distance between their nuclei is approximately equal to the sum of their van der Waals radii. Although they are individually very weak, such van der Waals attractions can become important when two macromolecular surfaces fit together very closely, because many atoms are involved.

Note that when two atoms form a covalent bond, the centers of the two atoms, the two atomic nuclei, are much closer together than the sum of the two van der Waals radii. Thus three covalent bonds and their bond length are depicted below as follows:

1. Two non-bonded carbon atoms that are positioned 0.4 nanometers apart. 2. Two carbon atoms held by a single covalent bond, the distance between their centers is 0.15 nanometers. 3. Two carbon atoms held by a double covalent bond, the distance between their centers is 0.13 nanometers.

Panel 3 reviews hydrogen bonds. The text reads, as already described for water, see Panel 2-2, pages 68-69; hydrogen bonds form when a hydrogen atom is sandwiched between two electron-attracting atoms, usually oxygen or nitrogen.

Hydrogen bonds are strongest when the three atoms are in a straight line.

An illustration shows two chemical structures. In the first structure, a central hydrogen atom is single bonded to an oxygen atom and hydrogen bonded to an oxygen atom. One oxygen atom has a free single bond and the other oxygen atom has a free double bond. In the second structure, a central hydrogen atom is single bonded to a nitrogen atom and hydrogen bonded to an oxygen atom. The nitrogen atom has two free single bonds and the oxygen atom has a free double bond.

Examples in macromolecules are shown below.

Amino acids in a polypeptide chain can be hydrogen-bonded together in a folded protein.

An illustration depicts a chemical structure in which a central carbon atom is single bonded to a hydrogen atom, R-group, nitrogen, and a carbon atom. The carbon atom is double bonded to an oxygen atom which is hydrogen bonded to a hydrogen atom. The hydrogen atom is single bonded to a nitrogen atom which is single bonded to a carbon atom. The carbon atom is single bonded to a hydrogen atom and R-group. The nitrogen atom single bonded to the central carbon atom is single bonded to a hydrogen atom. That hydrogen atom is hydrogen bonded to an oxygen atom which is double bonded to a carbon atom. The carbon atom is single bonded to a carbon atom. That carbon atom is single bonded to a hydrogen atom and R-group. A dashed line passes through the carbon and nitrogen atoms of the structure.

A text below reads, two bases, G and C, are hydrogen-bonded in a DNA double helix.

An illustration depicts a chemical structure of a DNA double helix. The structure shows a six membered ring hydrogen bonded to another six membered ring which is fused with a five membered ring.

The next paragraph is titled hydrogen bonds in water. The text reads, any two atoms that can form hydrogen bonds to each other can alternatively form hydrogen bonds to water molecules. Because of this competition with water molecules, the hydrogen bonds formed in water between two peptide bonds, for example, are relatively weak.

An illustration shows two water molecules with peptide bonds undergoing a reversible to form a product in which a hydrogen bond is formed between two peptide bonds. The peptide bonds are highlighted. Each peptide bond has a carbon single bonded to a nitrogen and double bonded to an oxygen atom; the nitrogen is further single bonded to a hydrogen atom which is hydrogen bonded to the oxygen of the water molecule on the reactants side. On the products side, the hydrogen atom of the peptide bond is hash bonded to oxygen of another peptide bond. In the forward reaction, 2 H subscript 2 O molecules are released. The reverse reaction uses 2 H subscript 2 O molecules.

Panel 4 describes electrostatic attractions. The text reads, electrostatic attractions occur both between fully charged groups, such as in an ionic bond, and between partially charged groups on polar molecules.

An illustration shows a blue sphere with a partial positive charge arranged closely to a yellow sphere with a partial negative charge. Electrostatic attraction between the two spheres is represented by wavy lines.

The text below reads, the force of attraction between the two partial charges, delta superscript plus and delta superscript minus, falls off rapidly as the distance between the charges increases.

The next paragraph is titled electrostatic attractions in water. The text reads, charged groups are shielded by their interactions with water molecules. Electrostatic attractions are therefore quite weak in water.

A chemical structure shows a central phosphorous atom single bonded to two oxygen ions that are negatively charged and double bonded to an oxygen atom. The structure is highlighted in yellow. The central phosphorous is also single bonded to an oxygen atom. A positively charged magnesium ion is also highlighted in yellow. Between the magnesium and phosphate group there are nine water molecules in which the oxygen of one water molecule is hydrogen bonded to the hydrogen of another water molecule. Two water molecules surround the magnesium ion.

Panel 1 shows monosaccharides. The text reads, monosaccharides usually have the general formula C H subscript 2 O n times, where n can be 3, 4, 5, or 6, and have two or more hydroxyl groups. They either contain an aldehyde group, written as a central carbon atom single bonded to a hydrogen atom and double bonded to an oxygen atom, and are called aldoses, or a ketone group, written as a carbon atom with two free single bonds and double bonded to an oxygen atom, and are called ketoses.

An illustration shows three chemical structures of aldoses and three chemical structures of ketoses for 3-carbon structures, or trioses,, 5-carbon structures, or pentoses, and 6-carbon structures, or hexoses.

The aldoses shown are glyceraldehyde, ribose, and glucose.

Glyceraldehyde has a 3-carbon structure with the following configuration: C 1 is single bonded to a hydrogen atom and double bonded to an oxygen atom and this group is highlighted. C 2, C 3 are each single bonded to a hydrogen atom and an O H group. C 3 is single bonded to an additional hydrogen atom.

Ribose has a 5-carbon structure with the following configuration: C 1 is single bonded to a hydrogen atom and double bonded to an oxygen atom and this group is highlighted in green color. C 2, C 3, and C 4 are each single bonded to a hydrogen atom and an O H group. C 5 is single bonded to two hydrogen atoms and an O H group.

Glucose has a 6-carbon structure with the following configuration: C 1 is single bonded to a hydrogen atom and double bonded to an oxygen atom and this group is highlighted in green color. C 2, C 4, and C 5 are each single bonded to a hydrogen atom on the left and an O H group on the right. C 3 is single bonded to a hydrogen atom on the right and an O H group on the left. C 6 is single bonded to two hydrogen atoms and an O H group.

The ketoses shown are dihydroxyacetone, ribulose, and fructose.

Dihydroxyacetone has a 3-carbon structure with the following configuration: C 1 and C 3 are single bonded to two hydrogen atoms and an O H group. C 2 is double bonded to an oxygen atom and is highlighted in green color.

Ribulose has a 5-carbon structure with the following configuration: C 1 and C 5 are single bonded to two hydrogen atoms and an O H group. C 3 and C 4 are single bonded to a hydrogen atom and an O H group. C 2 is double bonded to an oxygen atom and is highlighted in green color.

Fructose has a 6-carbon structure with the following configuration: C 1 and C 6 are each single bonded to two hydrogen atoms and an O H group. C 4 and C 5 are single bonded to a hydrogen atom on the left and an O H group on the right. C 3 is single bonded to a hydrogen bond on the right and an O H group on the left. C 2 is double bonded to an oxygen atom and is highlighted in green color.

Panel 2 describes ring formation. The text reads, in aqueous solution, the aldehyde or ketone group of a sugar molecule tends to react with a hydroxyl group of the same molecule, thereby closing the molecule into a ring.

The chemical structure and the ring configuration of glucose and ribose are shown. The chemical structure of glucose shows a six-carbon chain. C 1 is single bonded to a hydrogen atom and double bonded to an oxygen atom. C 2, C 4, and C 5 are single bonded to a hydrogen atom on the left and an O H group on the right. C 3 is single bonded to a hydrogen atom on the right and an O H group on the left. C 6 is single bonded to two hydrogen atoms and an O H group. The carbon atoms are numbered from 1 to 6. The ring structure of glucose shows a six-membered ring. C 1 and C 3 are single bonded to an O H group at the top and a hydrogen atom at the bottom. C 2 and C 4 are single bonded to a hydrogen atom at the top and an O H group at the bottom. C 5 is single bonded to a hydrogen atom at the bottom and a C H subscript 2 O H group. An oxygen atom is bonded outside between C 1 and C 5.

The chemical structure of ribose shows a five-carbon chain. C 1 is single bonded to a hydrogen atom and double bonded to an oxygen atom. C 2, C 3, and C 4 are single bonded to a hydrogen atom and an O H group. C 5 is single bonded to two hydrogen atoms and an O H group. The carbon atoms are numbered from 1 to 5. The ring structure of ribose shows a five membered ring. C 1 is single bonded to a hydrogen atom at the bottom and an O H group at the top. C 2 and C 3 are single bonded to a hydrogen atom at the top and an O H group at the bottom. C 4 is single bonded to a hydrogen atom at the bottom and a C H subscript 2 O H at the top. An oxygen atom is bonded outside between C 1 and C 4.

Panel 3 describes isomers. The text reads, many monosaccharides differ only in the spatial arrangement of atoms – that is, they are isomers. For example, glucose, galactose, and mannose have the same formula, C subscript 6 H subscript 12 O subscript 6, but differ in the arrangement of groups around one or two carbon atoms.

The structures of glucose, galactose, and mannose are shown as follows:

Glucose is a six-membered ring. C 1 and C 3 are single bonded to an O H group at the top and a hydrogen atom at the bottom. C 2 and C 4 are single bonded to a hydrogen atom at the top and an O H group at the bottom. C 5 is single bonded to a hydrogen atom at the bottom and a C H subscript 2 O H group. An oxygen atom is bonded outside between C 1 and C 5.

Galactose is a six-membered ring. C 1 and C 3 are single bonded to an O H group at the top and a hydrogen atom at the bottom. C 4 is also single bonded to an O H group at the top and a hydrogen atom at the bottom and this is highlighted in green color. C 2 is single bonded to a hydrogen atom at the top and an O H group at the bottom. C 5 is single bonded to a hydrogen atom at the bottom and a C H subscript 2 O H group. An oxygen atom is bonded outside between C 1 and C 5.

Mannose is a six-membered ring. C 1 and C 3 are single bonded to an O H group at the top and a hydrogen atom at the bottom. C 2 is also single bonded to an O H group at the top and a hydrogen atom at the bottom and this is highlighted in green color. C 4 is single bonded to a hydrogen atom at the top and an O H group at the bottom. C 5 is single bonded to a hydrogen atom at the bottom and a C H subscript 2 O H group. An oxygen atom is bonded outside between C 1 and C 5.

The text below reads, these small differences make only minor changes in the chemical properties of the sugars. But the differences are recognized by enzymes and other proteins and therefore can have major biological effects.

Panel 4 describes alpha and beta links. The text reads, the hydroxyl group on the carbon that carries the aldehyde or ketone can rapidly change from one position to the other. These two positions are called alpha and beta.

An illustration shows a reversible configuration of beta hydroxyl and alpha hydroxyl. The structure of beta hydroxyl shows an oxygen substituted six-membered ring in which C 1 is single bonded to an O H group at the top and has a free single bond at the bottom and is highlighted in green color. C 2, C 3, C 4, and C 5 have free single bonds attached.

A structure of alpha hydroxyl shows an oxygen substituted six membered ring in which C 1 is single bonded to an O H group at the bottom and has a free single bond at the top and is highlighted in green color. C 2, C 3, and C 4 have a free single bond at the bottom. C 5 has a free single bond at the top.

The text below reads, as soon as one sugar is linked to another, the alpha or beta form is frozen.

Panel 5 shows sugar derivatives. The text reads, the hydroxyl groups of a simple monosaccharide, such as glucose, can be replaced by other groups.

Three illustrations show the structure of glucuronic acid, glucosamine, and N-acetylglucosamine.

The first illustration shows the structure of glucuronic acid which has a six-membered ring. C 1 and C 3 are single bonded to an O H group at the top and a free single bond at the bottom. C 2 and C 4 are single bonded to an O H group at the bottom and a free single bond at the top. An oxygen atom is bonded in between C 5 and C 1. C 5 is single bonded to a carbon atom. The carbon atom is single bonded to an O H group and double bonded to an oxygen atom and this structure is highlighted in green color.

The second illustration shows the structure of glucosamine which has a six-membered ring. C 1 and C 3 are single bonded to an O H group at the top and a free single bond at the bottom. C 4 is single bonded to an O H group at the bottom and a free single bond at the top. C 5 is single bonded to a C H subscript 2 O H group at the top and a free single bond at the bottom. An oxygen atom is bonded in between C 5 and C 1. C 2 is single bonded to a hydrogen atom at the top and N H subscript 2 at the bottom in which N H subscript 2 is highlighted in green color.

The third illustration shows the structure of N-acetyglucosamine which has a six membered ring. C 1 and C 3 are single bonded to an O H group at the top and a free single bond at the bottom. C 4 is single bonded to an O H group at the bottom and a free single bond at the top. C 5 is single bonded to a C H subscript 2 O H group at the top and a free single bond at the bottom. An oxygen atom is bonded in between C 5 and C 1. C 2 is single bonded to a hydrogen atom at the top and N H at the bottom. N H is single bonded to a carbon atom which is double bonded to an oxygen atom and single bonded to C H subscript 3 and this structure is highlighted in green color.

Panel 6 shows disaccharides. The text reads, the carbon that carries the aldehyde or the ketone can react with any hydroxyl group on a second sugar molecule to form a disaccharide. Three common disaccharides are maltose, which is comprised of glucose plus glucose, lactose, which is comprised of galactose plus glucose, and sucrose, which is comprised of glucose plus fructose.

The reaction forming sucrose is shown here.

Alpha-glucose combines with beta fructose to form sucrose; a water molecule is released in the process. The chemical structures of alpha glucose, beta fructose, and sucrose are shown.

In alpha glucose, a six-membered ring in which C 1, C 2, and C 4 is single bonded to an O H group at the bottom and a free single bond at the top. C 3 is single bonded to an O H group at the top and a free single bond at the bottom. C 5 is single bonded to a C H subscript 2 O H at the top and a free single bond at the bottom. An oxygen atom is bonded outside between C 5 and C 1. The H of O H group bonded with C 1 is highlighted in green color. In beta fructose, a five-membered ring in which C 1 is single bonded to C H subscript 2 O H at the bottom and has a free single bond at the top. C 2 is single bonded to an O H group at the top and a free single bond at the bottom. C 3 is single bonded to an O H group at the bottom and a free single bond at the top. C 4 is single bonded to an O H group at the bottom which is highlighted in green color and C H subscript 2 O H at the top. An oxygen atom is replaced at C 5. In sucrose, a central oxygen atom is single bonded to C 1 of the six-membered ring and C 4 of the five-membered ring.

Panel 7 shows oligosaccharides and polysaccharides. The text reads, large linear and branched molecules can be made from simple repeating sugar subunits. Short chains are called oligosaccharides, and long chains are called polysaccharides. Glycogen, for example, is a polysaccharide made entirely of glucose subunits joined together.

An illustration shows linear and branched molecules of glycogen in which 26 small six-membered rings are linked together to form a concave down curve shape with branches.

Panel 8 shows complex oligosaccharides. The text reads, in many cases, a sugar sequence is non-repetitive, allowing the formation of a diverse array of distinct molecules. Such complex oligosaccharides are usually linked to proteins or to lipids, as is this oligosaccharide, which is part of a cell-surface molecule that defines a particular blood group.

An illustration shows a structure of a complex oligosaccharide which has four six-membered rings. In the first six-membered ring, C 1 has a free single bond at the top and is single bonded to an oxygen atom at the bottom which also is single bonded to C 3 of second six-membered ring. C 2 is single bonded to N H at the bottom and has a free single bond. N H is single bonded to a carbon atom which is single bonded to C H subscript 3 and double bonded to an oxygen atom. C 3 and C 4 are single bonded to an O H group at the top and has a free single bond at the bottom. C 5 is single bonded to C H subscript 2 O H. C 6 is replaced by an oxygen atom. In the second six membered ring, C 1 is single bonded to an oxygen atom at the top that is single bonded to C 4 of fourth six-membered ring. C 2 is single bonded to an oxygen atom at the bottom that is single bonded to C 1 of third six-membered ring and a free single bond at the top. C 3 is single bonded to an oxygen atom at the top that is single bonded to C 1 of the first six-membered ring and a free single bond at the bottom. C 4 is single bonded to an O H group at the top and a free single bond at the bottom. C 5 is single bonded to C H subscript 2 O H at the top and a free single bond at the bottom. C 6 is replaced by an oxygen atom. In the third six-membered ring, C 1 is single bonded to an oxygen atom at the top that is single bonded to C 2 of the second six-membered ring and a free single bond at the bottom. C 2 is single bonded to a free single bond at the top and bottom. C 3 and C 4 are single bonded to an O H group at the bottom and a free single bond at the top. C 5 is single bonded to C H subscript 3 at the bottom and a free single bond at the top. C 6 is replaced by an oxygen atom. In the fourth six-membered ring, C 1 is single bonded to an oxygen atom at the top and a free single bond at the bottom. C 2 is single bonded to N H at the bottom and has a free single bond. N H is single bonded to a carbon atom which is single bonded to C H subscript 3 and double bonded to an oxygen atom. C 3 is single bonded to an O H group at the top and has a free single bond at the bottom. C 4 is single bonded to an oxygen atom at the bottom that is single bonded to C 1 of the second six-membered ring and has a free single bond at the top. C 5 is single bonded to C H subscript 2 O H. C 6 is replaced by an oxygen atom.

Text reads, hundreds of different kinds of fatty acids exist. Some have one or more double bonds in their hydrocarbon tail and are said to be unsaturated. Fatty acids with no double bonds are saturated.

A space filling model and a carbon skeleton of an unsaturated acid, represented by oleic acid, and a saturated acid, represented by stearic acid, are shown. The space filling model of oleic acid shows black, white, and red spheres bonded together in right angle bracket shape. The carbon skeleton depicts a line angle formula with an eighteen carbon chain. C 1 is single bonded to a carbon atom which is single bonded to an oxygen ion negatively charged and double bonded to an oxygen atom. C 9 and C 10 are double bonded to each other. A text corresponding to the double bond reads, this double bond is rigid and creates a kink in the chain. The rest of the chain is free to rotate about the other C-C bonds. The space filling model of stearic acid shows black, white, and red spheres bonded together in a column like shape. The carbon skeleton shows an eighteen carbon chain. C 1 is single bonded to a carbon atom which is single bonded to a negatively charged oxygen ion and double bonded to an oxygen atom.

Panel 2 shows triaglycerols. The text reads, fatty acids are stored in cells as an energy reserve, such as fats and oils, through an ester linkage to glycerol to form triacylglycerols.

A chemical structure of glycerol is shown. The structure shows a three carbon chain with the following configuration: C 1 and C 3 form a C H subscript 2 group and are each single bonded to an O H group. C 2 is single bonded to an H atom and to an O H group. The fatty acid chain shows three linear carbon chains that substitute the H atom of each O H group in glycerol.

Panel 3 discusses the carboxyl group in fatty acids. The text reads, if free, the carboxyl group of a fatty acid will be ionized.

An illustration below shows a sixteen carbon chain. The terminal carbon atom is single bonded to a negatively charged oxygen and double bonded to an oxygen atom.

The text below reads, but more often it is linked to other groups to form either esters.

A sixteen carbon chain is shown, in which the terminal carbon is single bonded to an oxygen atom and double bonded to another oxygen atom. The single bonded oxygen atom is single bonded to a carbon, to which three open single bonds are attached.

A text below reads, or amides.

A sixteen carbon chain is shown. The terminal carbon is single bonded to a nitrogen atom and double bonded to an oxygen atom. The nitrogen atom has a free single bond and a single bond to a hydrogen atom.

Panel 4 describes phospholipids. The text reads, phospholipids are the major constituents of cell membranes. An illustration shows the general structure of a phospholipid. The illustration shows a central C H group single bonded to two C H subscript 2 groups. One C H subscript 2 group is single bonded to an oxygen atom and this structure is highlighted in green color. The other C H subscript 2 group is single bonded to a hydrophobic fatty acid tail and the C H group is also single bonded to a hydrophobic fatty acid tail. The oxygen atom is single bonded to a phosphate group which is highlighted in yellow. In the phosphate group, a central phosphorous atom is double bonded to an oxygen atom, single bonded to a negatively charged oxygen ion and an oxygen atom. The oxygen atom is single bonded to a polar group. The polar group is highlighted in blue color. The polar group and the phosphate group is labeled as hydrophilic head. A space filling model of phosphatidylcholine beside depicts black, white, red, yellow, and blue spheres that are bonded together. The blue sphere is amongst black and white spheres and is labeled choline.

Text below reads, in phospholipids, two of the O H groups in glycerol are linked to fatty acids, while the third O H group is linked to phosphoric acid. The phosphate, which carries a negative charge, is further linked to one of a variety of small polar groups, such as choline.

Panel 5 describes lipid aggregates. A text reads, fatty acids have a hydrophilic head and a hydrophobic tail. An illustration beside the text depicts a red sphere linked to a pink vertical thick line.

A text below reads, their derivatives can form larger aggregates held together by hydrophobic forces.

A schematic shows a yellow sphere with a diameter of 200 nanometer or more. The accompanying text reads, Triacylglycerols form large spherical fat droplets in the cell cytoplasm.

An illustration depicts two concentric circles. An enlarged view of two circles shows two columns of red spheres arranged such that their tails face each other toward the center and the heads are along the periphery. Accompanying text reads, phospholipids and glycolipids form self-sealing lipid bilayers, which are the basis for all cell membranes.

Panel 7 shows steroids. The text reads, steroids have a common multiple-ring structure.

The structure of cholesterol and testosterone are shown.

Cholesterol is found in many cell membranes. The structure of cholesterol shows three six membered rings and a five membered ring that are fused. The first six membered ring is bonded to an O H group. The five membered ring has a carbon side chain attached to it.

Testosterone is a male sex hormone. The structure of testosterone shows three six membered rings and a five membered ring that are fused. The first six membered ring is double bonded to an oxygen atom. The five membered ring is single bonded to an O H group.

Panel 8 describes glycolipids. The text reads, like phospholipids, these compounds are composed of a hydrophobic region, containing two long hydrocarbon tails, and a polar region, which contains one or more sugars. Unlike phospholipids, there is no phosphate.

The structure of a simple glycolipid is shown. The structure shows two line angle formulas. The first line angle formula is an eighteen carbon chain. C 1 forms a C H subscript 2 group. C H subscript 2 is single bonded to an oxygen atom that is single bonded to galactose. The galactose is labeled as a sugar. C 2, C 4 and C 5 are each single bonded to a hydrogen atom. There is a double bond between C 4 and C 5. C 3 is single bonded to a hydrogen atom and an O H group. The second line formula is an eighteen carbon chain. C 1 is replaced by a carbon atom. C 1 is single bonded to an N H group and double bonded to an oxygen atom. The N H group is single bonded to C 2 of the first line angle formula.

Panel 2 shows the structures of amino acids with basic side chains. The amino acids shown are lysine, arginine, and histidine.

The first illustration shows the structure of lysine, abbreviated to L Y S or K, which has a five carbon chain. C 1 is single bonded to a hydrogen atom, a nitrogen atom, and a carbon atom. The nitrogen atom is single bonded to a hydrogen atom and has a free single bond. The carbon atom is double bonded to an oxygen atom and has a free single bond. C 2, C 3, C 4, and C 5 are replaced by C H subscript 2 groups. C 5 is single bonded to N H subscript 3 superscript plus group. The C H subscript 2 groups and N H subscript 3 superscript plus are indicated to be the side chain.

The second illustration shows the structure of arginine, abbreviated to A R G or R, which has a four carbon chain. C 1 is single bonded to a hydrogen atom, a nitrogen atom, and a carbon atom. The nitrogen atom is single bonded to a hydrogen atom and has a free single bond. The carbon atom is double bonded to an oxygen atom and has a free single bond. C 2, C 3, and C 4 are replaced by C H subscript 2 groups. C 4 is single bonded to an N H group which is single bonded to a carbon atom that is single bonded to an N H subscript 2 group and double bonded to an N H subscript 2 superscript plus group; a text corresponding to this carbon and its branches reads, this group is very basic because its positive charge is stabilized by resonance. C 2 through the branch of N H subscript 2 groups is indicated as the side chain.

The third illustration shows the structure of histidine, abbreviated to H I S or H, in which a central carbon atom is single bonded to a carbon atom, nitrogen atom, hydrogen atom, and a C H subscript 2 group. The nitrogen atom is single bonded to a hydrogen atom and has a free single bond. The carbon atom is double bonded to an oxygen atom and has a free single bond. The C H subscript 2 group is single bonded to a six membered ring. In the six membered ring, C 1 and C 6 and C 2 and C 3 are doubled bonded to each other. C 1 and C 4 are replaced by a C H group. C 2 is replaced by N H superscript plus. C 5 is replaced by an N H group. C 6 is replaced by a carbon atom. The corresponding text of nitrogen of N H and N H superscript plus reads, these nitrogens have a relatively weak affinity for an H superscript plus and are only partly positive at neutral p H. The C H subscript 2 group and the six membered ring are indicated as the side chain.

Panel 4 explains optical isomers. The text reads, the alpha-carbon atom is asymmetric, allowing for two mirror-image, or stereo, isomers, L and D.

An illustration shows a mirror-image of a ball and stick model of L and D isomers of amino acids. In L, a central alpha-carbon atom is single bonded to an N H subscript 3 superscript plus group on the left, a C O O superscript minus group on the right, a hydrogen atom at the top, and a side chain R at the bottom. In D, which is the mirror-image of L, a central alpha-carbon atom is single bonded to an N H subscript 3 superscript plus group on the right, a C O O superscript minus group on the left, a hydrogen atom at the top, and a side chain R at the bottom.

A text below the illustration reads, proteins contain exclusively L-amino acids.

Panel 5 discusses peptide bonds. The text reads, in proteins, amino acids are joined together by an amide linkage, called a peptide bond.

An illustration shows a chemical reaction in which two amino acids react and form a product with the release of water. In the first amino acid, a central carbon atom is single bonded to a hydrogen atom at top, carbon atom at the right, a side chain R at the bottom, and a nitrogen atom at the left. The nitrogen atom is single bonded to two hydrogen atoms. The carbon atom is double bonded to an oxygen atom and single bonded to an O H group. In the second amino acid, a central carbon atom is single bonded to a hydrogen atom at the bottom, carbon atom at the right, a side chain R at the top, and a nitrogen atom at the left. The carbon atom is single bonded to an O H group and double bonded to an oxygen atom. The nitrogen atom is single bonded to two hydrogen atoms in which one hydrogen atom. It is indicated the H subscript 2 O is released during the reaction. In the product, there is a five carbon chain in which C 3 is replaced by a nitrogen atom. C 1 is single bonded to an O H group and double bonded to an oxygen atom. C 2 is single bonded to a hydrogen atom at the bottom and a side chain R at the top. C 3 is single bonded to a hydrogen atom. C 4 is double bonded to an oxygen atom. C 5 is single bonded to a hydrogen atom at the top, a side chain R at the bottom, and a nitrogen atom. The nitrogen atom is single bonded to two hydrogen atoms. The single bond between C 3 and C 4 is labeled as a peptide bond. The nitrogen and carbon structures at C 3 and C 4 are shown to be in the same plane. The text above the product reads, the four atoms involved in each peptide bond form a rigid planar unit. There is no rotation around the C N bond.

A text below the reaction reads, proteins are long polymers of amino acids linked by peptide bonds, and they are always written with the N-terminus toward the left. Peptides are shorter, usually fewer than 50 amino acids long. The sequence of this tripeptide is histidine hyphen cysteine hyphen valine.

An illustration shows the chemical structure of histidine hyphen cysteine hyphen valine. In histidine, a central carbon atom is single bonded to a hydrogen atom at the top, N H subscript 3 superscript plus group at the left, and C H subscript 2 group at the bottom, and a C N bond at the right. The N H subscript 3 superscript plus is labeled amino terminus, or N-terminus. The C H subscript 2 group is single bonded to a six membered ring, this unit is the side chain. In the six membered ring, C 1 and C 6 and C 2 and C 3 are doubled bonded to each other. C 1 and C 4 are replaced by a C H group. C 2 is replaced by N H superscript plus. C 5 is replaced by N H group. C 6 is replaced by a carbon atom. In C N bond, a carbon atom is double bonded to an oxygen atom at top and single bonded to a nitrogen atom which is single bonded to a hydrogen atom at the bottom and a carbon atom of cysteine on the right. The C N bond is identified as a peptide bond. In cysteine, a central carbon atom is single bonded to a nitrogen atom of C N bond on the left, a carbon atom of C N bond on the right, these two bonds allow rotation. The central carbon is also bound to a C H subscript 2 group at the top. The C H subscript 2 is single bonded to S H group, this unit is identified as the side chain. In the C N bond on the right, a carbon atom is double bonded to an oxygen atom at the bottom and single bonded to a nitrogen atom on the right which is single bonded to a hydrogen atom at top and carbon atom of valine on the right. The C N bond is identified as a peptide bond. In valine, a central carbon atom is single bonded to a hydrogen atom at the top, C O O superscript minus on the right, and a C H group at the bottom. The C H group is single bonded to two C H subscript 3, this unit is identifed as the side chain. The C O O superscript minus is labeled the carboxyl terminus, or C–terminus.

Panel 7 shows the structures of amino acids with uncharged polar side chains. The amino acids asparagine, glutamine, serine, threonine, and tyrosine are shown. The structure of asparagines, abbreviated to A S N or N, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 group with a single bond to a carbon atom which is double bonded to an oxygen atom and single bonded to an N H subscript 2 group.

The structure of glutamine, abbreviated G L N or Q, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 group with a single bond to another C H subscript 2 group which is single bonded to a carbon atom. The carbon atom is double bonded to an oxygen atom and single bonded to an N H subscript 2 group. A text corresponding to the N H subscript 2 groups of A S N and G L N reads, although the amide N is not charged at neutral p H, it is polar.

The structure of serine, abbreviated S E R or S, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 group with a single bond to an O H group.

The structure of threonine, abbreviated T H R or T, shows an amino acid structure bound to an R group. The R group consists of a C H group with a single bond to an O H group and to a C H subscript 3 group.

The structure of tyrosine, abbreviated T Y R or T, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 group with a single bond to a six membered ring. In the six membered ring, C 1 and C 2, C 3 and C 4, and C 5 and C 6 are double bonded to each other. C 3 is single bonded to an O H group. A text corresponding to O H groups of S E R, T H R, and T Y R reads the –O H group is polar.

Panel 8 shows the structures of amino acids with uncharged polar side chains. The amino acids shown are alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan, glycine, and cysteine.

Alanine, abbreviated A L A or A, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 3 group.

Valine, abbreviated V A L or V, shows an amino acid structure bound to an R group. The R group consists of a C H group with a single bonded to two C H subscript 3 groups.

Leucine, abbreviated L E U or L, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 group with a single bond to a C H group which is single bonded to two C H subscript 3 groups.

Isoleucine, abbreviated I L E or I, shows an amino acid structure bound to an R group. The R group consists of a C H group single bonded to a C H subscript 3 and a C H subscript 2. The C H subscript 2 group is single bonded to a C H subscript 3.

Proline, abbreviated P R O or P, shows an amino acid structure bound to an R group. The R group is bound at the nitrogen atom and the carbon atom. The nitrogen atom is single bonded to a C H subscript 2 group. The carbon atom is bound to another C H subscript 2 group. Both C H subscript 2 groups are bound to the same C H subscript 2 group. Corresponding text reads, actually an imino acid.

Phenylalanine, abbreviated P H E or F, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 single bonded to a six membered ring. In the six membered ring, C 1 and C 2, C 3 and C 4, and C 5 and C 6 are double bonded to each other.

Methionine, abbreviated M E T or M, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 single bonded to a C H subscript 2 group which is single bonded to a sulfur atom. The sulfur atom is single bonded to C H subscript 3 group.

Tryptophan, abbreviated T R P or W, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 single bonded to a five membered ring. The five membered ring is bonded together with a six membered ring in which C 1 is replaced by N H group, C 2 and C 3; C 4 and C 9; C 5 and C 6; and C 7 and C 8 are double bonded to each other.

Glycine, abbreviated G L Y or G, shows an amino acid structure bound to an R group. The R group consists of a single bonded hydrogen atom. Cysteine, abbreviated C Y S or C, shows an amino acid structure bound to an R group. The R group consists of a C H subscript 2 single bonded to an S H group.

Panel 1 shows nucleic acid bases. An illustration shows the chemical structure of pyrimidine and purine. The text reads, the bases are nitrogen-containing ring compounds, either pyrimidines or purines.

Pyrimidine shows a six membered ring in which the carbons are numbered from 1 to 6 in a counterclockwise direction. C 1 and C 3 are replaced by nitrogen atom. Pyrimidine branches to three different chemical structures: uracil, cytosine, and thymine. Uracil depicts a six membered ring in which C 5 and C 6 are double bonded to each other. C 1 and C 3 are replaced by an N H group. C 2 and C 4 are replaced by a carbon atom which is doubled bonded to an oxygen atom. C 5 and C 6 are replaced by a C H group. Cytosine shows a six membered ring in which C 3 and C 4 and C 5 and C 6 are doubled bonded to each other. C 1 is replaced by an N H group. C 2 is replaced by a carbon atom which is double bonded to an oxygen atom. C 3 is replaced by a nitrogen atom. C 4 is replaced by a carbon atom which is single bonded to an N H subscript 2 group. C 5 and C 6 are replaced by a C H group. Thymine shows a six membered ring in which C 5 and C 6 are double bonded to each other. C 1 and C 3 are replaced by an N H group. C 2 and C 4 are replaced by a carbon atom which is double bonded to an oxygen atom. C 5 is replaced by a carbon atom which is single bonded to a C H subscript 3 group. C 6 is replaced by a C H group.

Purine shows a six membered ring bonded to a five membered ring in which carbons are numbered from 1 to 6 in clockwise direction in the six membered ring and 7 to 9 in counterclockwise direction in the five membered ring. C 1, C 3, C 7, and C 9 are replaced by nitrogen atom. Purine branches to two chemical structures: adenine and guanine. Adenine shows a six membered ring bonded with a five membered ring. C 1 and C 6, C 2 and C 3, C 4 and C 5, C 7 and C 8 are double bonded. C 1, C 3, and C 7 are replaced by a nitrogen atom. C 4 and C 5 are replaced by a carbon atom. C 2 and C 8 are replaced by C H group. C 6 is replaced by a carbon atom which is single bonded to N H subscript 2 group. C 9 is replaced by N H group. Guanine depicts a six membered ring bonded together with a five membered ring. C 2 and C 3, C 4 and C 5, and C 7 and C 8 are double bonded. C 1 and C 9 are replaced by N H group. C 2 is replaced by a carbon atom which is single bonded to N H subscript 2 group. C 4 and C 5 are replaced by a carbon atom. C 6 is replaced by a carbon atom which is double bonded to an oxygen atom. C 7 is replaced by nitrogen atom. C 8 is replaced by C H group.

A text reads, a nucleotide consists of a nitrogen-containing base, a five-carbon sugar, and one or more phosphate groups.

The chemical structure of a nucleotide shows a six membered ring (highlighted in green color) labeled base, a five membered ring (highlighted in blue color) labeled sugar, and a phosphate group (highlighted in yellow color). In base, C 3 and C 4 and C 5 and C 6 are double bonded to each other. C 1 and C 3 are replaced by a nitrogen atom. C 2 is doubled bonded to an oxygen atom. C 4 is single bonded to N H subscript 2. In sugar, C 1 is single bonded to a nitrogen atom of C 1 of base above the ring, and has a free single bond below the ring. C 2 and C 3 are single bonded to O H group below the ring and has a free single bond above the ring. C 4 has a free single bond below the ring and is single bonded to C H subscript 2 group above the ring. C 5 is replaced by an oxygen atom. C 1, C 2, C 3, C 4, and C H 2 are labeled 1 prime, 2 prime, 3 prime, 4 prime, and 5 prime. C H subscript 2 is single bonded to an oxygen atom which is single bonded to a phosphate group. Texts reads, nucleotides are the subunits of the nucleic acids.

Panel 5 shows sugars. An illustration shows a five membered ring labeled Pentose a five-carbon sugar. C 4 is single bonded to a carbon atom above the ring. C 5 is replaced by an oxygen atom. C 1, C 2, C 3, C 4, and the carbon atom are labeled as 1 prime, 2 prime, 3 prime, 4 prime, and 5 prime. A text below the illustration reads, each numbered carbon on the sugar of a nucleotide is followed by a prime mark; therefore, one speaks of the 5-prime carbon, etc.

Two arrows from the five membered ring branch out toward the right and a text between the arrows reads, two kinds of pentoses are used. The branched arrows show the structure of Beta-D-ribose and Beta-D-2-deoxyribose.

Beta-D-ribose shows a five membered ring in which C 5 is replaced by an oxygen atom. C 1 is single bonded to an O H group above the ring and a hydrogen atom below the ring. C 2 is single bonded to a hydrogen atom above the ring and an O H group below the ring. C 3 is single bonded to a hydrogen atom above the ring and an O H group below the ring. C 4 is single bonded to a hydrogen atom below the ring and a C H subscript 2 O H group above the ring. A text beside reads, Beta-D-ribose is used in ribonucleic acid, or R N A.

Beta-D-2-deoxyribose shows a five membered ring in which C 5 is replaced by an oxygen atom. C 1 is single bonded to an O H group above the ring and a hydrogen atom below the ring. C 2 is single bonded to a hydrogen atom above the ring and a hydrogen atom below the ring. C 3 is single bonded to a hydrogen atom above the ring and an O H group below the ring. C 4 is single bonded to a hydrogen atom below the ring and a C H subscript 2 O H group above the ring. A text beside reads, Beta-D-2-deoxyribose is used in deoxyribonucleic acid, or DNA.

Panel 8 describes additional functions of nucleotides and their derivatives. The text reads, as nucleoside di- and triphosphates, they carry chemical energy in their easily hydrolyzed phosphoanhydride bonds.

1.) A chemical structure shows a six membered ring bonded with a five membered ring in which C 1 and C 2, C 3 and C 4, C 5 and C 9 are double bonded to each other. C 1, C 3, C 6, and C 8 are replaced by a nitrogen atom. C 4 is single bonded to N H subscript 2. C 8 is single bonded to C 1 of a five membered ring. In the five membered ring, C 2 and C 3 are single bonded to O H group below the ring and has a free single bond above the ring. C 4 is single bonded to C H subscript 2 above the ring and has a free single bond below the ring. C 5 is replaced by an oxygen atom. C H subscript 2 is single bonded to an oxygen atom which is single bonded to three phosphate groups. The bond between the phosphate groups is labeled phosphoanhydride bonds. A text below reads, example: A T P.

2.) They combine with other groups to form coenzymes.

A chemical structure shows an eleven carbon chain. C 5 and C 9 are replaced by a nitrogen atom. C 1, C 6, C 7, C 10, and C 11 are single bonded to two hydrogen atoms. C 2 is single bonded to two C H subscript 3. C 4 and C 8 are double bonded to an oxygen atom. C 5 and C 9 are single bonded to a hydrogen atom. C 1 is also single bonded to a phosphate group which is single bonded to a phosphate group that is single bonded to an oxygen atom. The oxygen atom is single bonded to C H subscript 2 of C 4 of a five membered ring. In the five membered ring, C 2 is single bonded to an O H group above the ring and has a free single bond below the ring. C 3 is single bonded to an oxygen atom below the ring which is single bonded to a phosphate group and has a free single bond above the ring. C 4 has a free single bond below the ring. C 5 is replaced by an oxygen atom. C 1 has a free single bond below the ring and single bonded to nitrogen atom of C 9 of a five membered ring which is bonded together with a six membered ring. In the five membered ring bonded with a six membered ring, C 1, C 3, C 7, and C 9 are replaced by a nitrogen atom. C 6 is single bonded to N H subscript 2. C 1 and C 6, C 2 and C 3, C 4 and C 5, C 7 and C 8 are double bonded to each other. A text below reads, example: coenzyme A, or C o A.

3.) They are used as small intracellular signaling molecules in the cell.

A chemical structure shows a six membered ring bonded with a five membered ring in which C 1 and C 6, C 2 and C 3, C 4 and C 5, and C 7 and C 8 are double bonded to each other. C 1, C 3, C 7, and C 9 are replaced by a nitrogen atom. C 6 is single bonded to N H subscript 2 group. C 9 is single bonded to C 1 of a five membered ring. In the five membered ring, C 1 has a free single bond below the ring. C 2 is single bonded to O H group below the ring and has a free single bond above the ring. C 3 is single bonded to an oxygen atom below the ring and has a free single bond above the ring. C 5 is replaced by an oxygen atom. C 4 has a free single bond below the ring and is single bonded to C H subscript 2 group above the ring. The C H subscript 2 group is single bonded to an oxygen atom which is single bonded to a phosphorous atom. The phosphorous atom is double bonded to an oxygen atom on the left, single bonded to an oxygen ion which is negatively charged at the bottom, and an oxygen atom on the right which is bonded with C 3 of a five membered ring. A text beside reads, example: cyclic A M P.