Carbohydrate Structures -

Ribulose


Carbohydrate Structures -

PROBLEM Look up the structure of D-talose in Figure 25.4, and draw the $\beta$ anomer in its pyranose form. 25-48 Identify the ring substituents as axial or equatorial.


Carbohydrate Reactions -

PROBLEM Draw structures for the products you would expect to obtain from reaction of $\beta$-D-talopyranose with 25-49 each of the following reagents:
(a) $\mathrm{NaBH}_{4}$ in $\mathrm{H}_{2} \mathrm{O}$
(b) Warm dilute $\mathrm{HNO}_{3}$
(c) $\mathrm{Br}_{2}, \mathrm{H}_{2} \mathrm{O}$
(d) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}, \mathrm{HCl}$
(e) $\mathrm{CH}_{3} \mathrm{I}, \mathrm{Ag}_{2} \mathrm{O}$
(f) $\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}$, pyridine


Carbohydrate Reactions -

PROBLEM How many D-2-ketohexoses are possible? Draw them. 25-50


Carbohydrate Reactions -

PROBLEM One of the D-2-ketohexoses is called sorbose. On treatment with $\mathrm{NaBH}_{4}$, sorbose yields a mixture of 25-51 gulitol and iditol. What is the structure of sorbose?

PROBLEM Another D-2-ketohexose, psicose, yields a mixture of allitol and altritol when reduced with $\mathrm{NaBH}_{4}$. 25-52 What is the structure of psicose?


Carbohydrate Reactions -

PROBLEM L-Gulose can be prepared from D-glucose by a route that begins with oxidation to D-glucaric acid, 25-53 which cyclizes to form two six-membered-ring lactones. Separating the lactones and reducing them with sodium amalgam gives D -glucose and L-gulose. What are the structures of the two lactones, and which one is reduced to L -gulose?


Carbohydrate Reactions -

PROBLEM Gentiobiose, a rare disaccharide found in saffron and gentian, is a reducing sugar and forms only
25-54 D-glucose on hydrolysis with aqueous acid. Reaction of gentiobiose with iodomethane and $\mathrm{Ag}_{2} \mathrm{O}$ yields an octamethyl derivative, which can be hydrolyzed with aqueous acid to give 1 equivalent of 2,3,4,6-tetra-O-methyl-D-glucopyranose and 1 equivalent of 2,3,4-tri-O-methyl-D-glucopyranose. If gentiobiose contains a $\beta$-glycoside link, what is its structure?


General Problems -

PROBLEM All aldoses exhibit mutarotation. For example, $\alpha$-D-galactopyranose has $[\alpha]_{D}=+150.7$, and
25-55 $\beta$-D-galactopyranose has $[\alpha]_{D}=+52.8$. If either anomer is dissolved in water and allowed to reach equilibrium, the specific rotation of the solution is +80.2 . What are the percentages of each anomer at equilibrium? Draw the pyranose forms of both anomers.


General Problems -

PROBLEM What other D aldohexose gives the same alditol as D-talose? 25-56

PROBLEM Which of the eight D aldohexoses give the same aldaric acids as their L enantiomers? 25-57

PROBLEM Which of the other three D aldopentoses gives the same aldaric acid as D-lyxose? 25-58


General Problems -

PROBLEM Draw the structure of L-galactose, and then answer the following questions:
25-59 (a) Which other aldohexose gives the same aldaric acid as L-galactose on oxidation with warm $\mathrm{HNO}_{3}$ ?
(b) Is this other aldohexose a D sugar or an L sugar?
(c) Draw this other aldohexose in its most stable pyranose conformation.


General Problems -

PROBLEM Amygdalin, or laetrile, is a cyanogenic glycoside first isolated in 1830 from almond and apricot 25-60 seeds. If acidic hydrolysis of amygdalin liberates HCN, along with benzaldehyde cyanohydrin with gentiobiose (Problem 25-54), what is its structure?


General Problems -

PROBLEM Trehalose is a nonreducing disaccharide that is hydrolyzed by aqueous acid to yield 2 equivalents of
25-61 D-glucose. Methylation followed by hydrolysis yields 2 equivalents of 2,3,4,6-tetra- $O$-methylglucose. How many structures are possible for trehalose?


General Problems -

PROBLEM Trehalose (Problem 25-61) is cleaved by enzymes that hydrolyze $\alpha$-glycosides but not by enzymes
25-62 that hydrolyze $\beta$-glycosides. What is the structure and systematic name of trehalose?
PROBLEM Isotrehalose and neotrehalose are chemically similar to trehalose (Problems 25-61 and 25-62)
25-63 except that neotrehalose is hydrolyzed only by $\beta$-glycosidase enzymes, whereas isotrehalose is hydrolyzed by both $\alpha$ - and $\beta$-glycosidase enzymes. What are the structures of isotrehalose and neotrehalose?


General Problems -

PROBLEM D-Mannose reacts with acetone to give a diisopropylidene derivative (Problem 25-33) that is still 25-64 reducing toward Tollens' reagent. Propose a likely structure for this derivative.


General Problems -

PROBLEM Glucose and mannose can be interconverted (in low yield) by treatment with dilute aqueous NaOH .
25-65 Propose a mechanism.
PROBLEM Propose a mechanism to account for the fact that D-gluconic acid and D-mannonic acid are
25-66 interconverted when either is heated in pyridine solvent.
PROBLEM The cyclitols are a group of carbocyclic sugar derivatives having the general formulation 25-67 1,2,3,4,5,6-cyclohexanehexol. How many stereoisomeric cyclitols are possible? Draw them in their chair forms.


General Problems -

PROBLEM Compound $\mathbf{A}$ is a D aldopentose that can be oxidized to an optically inactive aldaric acid $\mathbf{B}$. On
25-68 Kiliani-Fischer chain extension, $\mathbf{A}$ is converted into $\mathbf{C}$ and $\mathbf{D} ; \mathbf{C}$ can be oxidized to an optically active aldaric acid $\mathbf{E}$, but $\mathbf{D}$ is oxidized to an optically inactive aldaric acid $\mathbf{F}$. What are the structures of A-F?


General Problems -

PROBLEM Simple sugars undergo reaction with phenylhydrazine, $\mathrm{PhNH}-\mathrm{NH}_{2}$, to yield crystalline derivatives 25-69 called osazones. The reaction is a bit complex, however, as shown by the fact that glucose and fructose yield the same osazone.
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0935.jpg?height=475&width=1061&top_left_y=1627&top_left_x=405)
(a) Draw the structure of a third sugar that yields the same osazone as glucose and fructose.
(b) Using glucose as the example, the first step in osazone formation is reaction of the sugar with phenylhydrazine to yield an imine called a phenylhydrazone. Draw the structure of the product.
(c) The second and third steps in osazone formation are tautomerization of the phenylhydrazone to give an enol, followed by elimination of aniline to give a keto imine. Draw the structures of both the enol tautomer and the keto imine.
(d) The final step is reaction of the keto imine with 2 equivalents of phenylhydrazine to yield the osazone plus ammonia. Propose a mechanism for this step.


General Problems -

PROBLEM When heated to $100{ }^{\circ} \mathrm{C}$, D-idose undergoes a reversible loss of water and exists primarily as 25-70 1,6-anhydro-D-idopyranose.
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0936.jpg?height=392&width=819&top_left_y=300&top_left_x=401)
(a) Draw D-idose in its pyranose form, showing the more stable chair conformation of the ring.
(b) Which is more stable, $\alpha$-D-idopyranose or $\beta$-D-idopyranose? Explain.
(c) Draw 1,6-anhydro-D-idopyranose in its most stable conformation.
(d) When heated to $100^{\circ} \mathrm{C}$ under the same conditions as those used for D-idose, D-glucose does not lose water and does not exist in a 1,6-anhydro form. Explain.


General Problems -

PROBLEM Acetyl coenzyme A (acetyl CoA) is the key intermediate in food metabolism. What sugar is present 25-71 in acetyl CoA?
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0936.jpg?height=475&width=988&top_left_y=1042&top_left_x=411)


CHAPTER 26 -

Biomolecules: Amino Acids, Peptides, and Proteins
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0937.jpg?height=1037&width=1888&top_left_y=449&top_left_x=235)


CHAPTER 26 -

FIGURE 26.1 The building blocks of life that we call proteins are aptly named after Proteus, the early Greek sea-god whose name means "first" or "primordial." (credit: modification of work by Coyau/Wikimedia Commons, CC BY-SA 3.0)


CHAPTER CONTENTS -

26.1 Structures of Amino Acids
26.2 Amino Acids and the Henderson-Hasselbalch Equation: Isoelectric Points
26.3 Synthesis of Amino Acids
26.4 Peptides and Proteins
26.5 Amino Acid Analysis of Peptides
26.6 Peptide Sequencing: The Edman Degradation
26.7 Peptide Synthesis
26.8 Automated Peptide Synthesis: The Merrifield Solid-Phase Method
26.9 Protein Structure
26.10 Enzymes and Coenzymes
26.11 How Do Enzymes Work? Citrate Synthase


CHAPTER CONTENTS -

WHY THIS CHAPTER? Continuing our look at the main classes of biomolecules, we'll focus in this chapter on amino acids, the fundamental building blocks from which up to 150,000 or so different proteins in our bodies are made. We'll then see how amino acids are incorporated into proteins and examine the structures of those proteins. Any understanding of biological chemistry would be impossible without this knowledge.


CHAPTER CONTENTS -

Proteins occur in every living organism, are of many different types, and have many different biological
functions. The keratin of skin and fingernails, the fibroin of silk and spider webs, and the estimated 50,000 or so enzymes that catalyze the biological reactions in our bodies are all proteins. Regardless of their function, all proteins have a fundamentally similar structure and are made up of many amino acids linked together in a long chain.


CHAPTER CONTENTS -

Amino acids, as their name implies, are difunctional. They contain both a basic amino group and an acidic carboxyl group.
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0938.jpg?height=297&width=613&top_left_y=502&top_left_x=775)


Alanine, an amino acid -

Their value as building blocks to make proteins stems from the fact that amino acids can join together into long chains by forming amide bonds between the $-\mathrm{NH}_{2}$ of one amino acid and the $-\mathrm{CO}_{2} \mathrm{H}$ of another. For classification purposes, chains with fewer than 50 amino acids are often called peptides, while the term protein is generally used for larger chains.


Alanine, an amino acid -

Many
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0938.jpg?height=258&width=1001&top_left_y=1053&top_left_x=619)


Alanine, an amino acid - 26.1 Structures of Amino Acids

We saw in Section 20.3 and Section 24.5 that a carboxyl group is deprotonated and exists as the carboxylate anion at a physiological pH of 7.3 , while an amino group is protonated and exists as the ammonium cation. Thus, amino acids exist in aqueous solution primarily in the form of a dipolar ion, or zwitterion (from the German zwitter, meaning "hybrid").
(uncharged)
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(zwitterion)


Alanine
Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They have large dipole moments, are relatively soluble in water but insoluble in hydrocarbons, and are crystalline with relatively high melting points. In addition, amino acids are amphiprotic; they can react either as acids or as bases, depending on the circumstances. In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton onto its $-\mathrm{CO}_{2}{ }^{-}$group to yield a cation. In aqueous base solution, the zwitterion is an acid that loses a proton from its $-\mathrm{NH}_{3}{ }^{+}$group to form an anion.


In acid solution
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0939.jpg?height=185&width=874&top_left_y=192&top_left_x=758)


In base solution
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0939.jpg?height=180&width=858&top_left_y=401&top_left_x=758)


The structures, abbreviations (both three- and one-letter), and $\mathrm{p} K_{\mathrm{a}}$ values of the 20 amino acids commonly found in proteins are shown in TABLE 26.1. All are $\boldsymbol{\alpha}$-amino acids, meaning that the amino group in each is a substituent on the $\alpha$ carbon-the one next to the carbonyl group. Nineteen of the twenty amino acids are primary amines, $\mathrm{RNH}_{2}$, and differ only in the nature of their side chain-the substituent attached to the $\alpha$ carbon. Proline is a secondary amine whose nitrogen and $\alpha$ carbon atoms are part of a five-membered pyrrolidine ring.


TABLE 26.1 The 20 Common Amino Acids in Proteins


| Name | Abbreviations |  | MW | Structure | $\begin{aligned} & \mathrm{p} K_{\mathrm{a}} \\ & \boldsymbol{\alpha}-\mathrm{CO}_{2} \mathrm{H} \end{aligned}$ | $\begin{aligned} & \mathrm{p} K_{\mathrm{a}} \\ & \boldsymbol{\alpha}-\mathrm{NH}_{3}+ \end{aligned}$ | $\mathrm{p} K_{\mathrm{a}}$
 side
 chain | pl |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| Neutral Amino Acids |  |  |  |  |  |  |  |  |
| Alanine | Ala | A | 89 | <smiles></smiles> | 2.34 | 9.69 | - | 6.01 |
| Asparagine | Asn | N | 132 | <smiles>NC(=O)CC@@HC(=O)[O-]</smiles> | 2.02 | 8.80 | - | 5.41 |
| Cysteine | Cys | C | 121 | <smiles>[NH3+]C(CS)C(=O)[O-]</smiles> | 1.96 | 10.28 | 8.18 | 5.07 |
| Glutamine | GIn | Q | 146 | <smiles>NC(=O)CCC@HC(=O)[O-]</smiles> | 2.17 | 9.13 | - | 5.65 |
| Glycine | Gly | G | 75 | <smiles></smiles> | 2.34 | 9.60 | - | 5.97 |
| Isoleucine | Ile | I | 131 | <smiles>CCC(C)C([NH3+])C(=O)[O-]</smiles> | 2.36 | 9.60 | - | 6.02 |

| Name | Abb | tions | MW | Structure | $\begin{aligned} & \mathrm{p} K_{\mathrm{a}} \\ & \boldsymbol{\alpha}-\mathrm{CO}_{2} \mathrm{H} \end{aligned}$ | $\begin{aligned} & \mathrm{p} K_{\mathrm{a}} \\ & \boldsymbol{\alpha}-\mathrm{NH}_{3}+ \end{aligned}$ | $\mathrm{p} K_{\mathrm{a}}$
 side
 chain | p/ |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| Leucine | Leu | L | 131 | <smiles>CC(C)CC@@HC(=O)[O-]</smiles> | 2.36 | 9.60 | - | 5.98 |
| Methionine | Met | M | 149 | <smiles>CSCCC@HC(=O)[O-]</smiles> | 2.28 | 9.21 | - | 5.74 |
| Phenylalanine | Phe | F | 165 | <smiles>NC@@HC(=O)[O-]</smiles> | 1.83 | 9.13 | - | 5.48 |
| Proline | Pro | P | 115 | <smiles>O=C([O-])C1CCC[NH2+]1</smiles> | 1.99 | 10.60 | - | 6.30 |
| Serine | Ser | S | 105 | <smiles>NC@@HC(=O)[O-]</smiles> | 2.21 | 9.15 | - | 5.68 |
| Threonine | Thr | T | 119 | <smiles></smiles> | 2.09 | 9.10 | - | 5.60 |
| Tryptophan | Trp | W | 204 | <smiles>[NH3+]C(Cc1c[nH]c2ccccc12)C(=O)[O-]</smiles> | 2.83 | 9.39 | - | 5.89 |
| Tyrosine | Tyr | Y | 181 | <smiles>NC@@Hcc1)C(=O)[O-]</smiles> | 2.20 | 9.11 | 10.07 | 5.66 |


| Name | Abb | ions | MW | Structure | $\begin{aligned} & \mathrm{p} K_{\mathrm{a}} \\ & \alpha-\mathrm{CO}_{2} \mathrm{H} \end{aligned}$ | $\begin{aligned} & \mathrm{p} K_{\mathrm{a}} \\ & \boldsymbol{\alpha}-\mathrm{NH}_{3}+ \end{aligned}$ | $\mathrm{p} K_{\mathrm{a}}$
 side
 chain | pl |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| Valine | Val | V | 117 | <smiles>CC(C)C@HC(=O)[O-]</smiles> | 2.32 | 9.62 | - | 5.96 |


Acidic Amino Acids -

| Aspartic acid | Asp | D | 133 | <smiles></smiles> | 1.88 | 9.60 | 3.65 | 2.77 |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| Glutamic acid | Glu | E | 147 | <smiles>COC(=O)CCC@HC(=O)[O-]</smiles> | 2.19 | 9.67 | 4.25 | 3.22 |


Acidic Amino Acids -

Basic Amino Acids
![](https://cdn.mathpix.com/cropped/2025_02_06_5556f7656cbdcaa0f9a7g-0941.jpg?height=1088&width=1697&top_left_y=1250&top_left_x=233)