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Biochemistry

Donald Voet, Judith G. Voet

Chapter 26

Amino Acid Metabolism - all with Video Answers

Educators

Chapter Questions

06:50

Problem 1

Write the reaction for the transamination of an amino acid in terms of Cleland notation (Section 14-5A).

Susan Hallstrom
Susan Hallstrom
Numerade Educator
04:05

Problem 2

Explain why the symptoms of the partial deficiency of a urea cycle enzyme may be attenuated by a low-protein diet.

Sana Riaz
Sana Riaz
Numerade Educator
03:14

Problem 3

Why are people on a high-protein diet instructed to drink lots of water?

Khalida Dawar
Khalida Dawar
Numerade Educator
04:58

Problem 4

A student on a particular diet expends $10,000 \mathrm{kJ} \cdot$ day $^{-1}$ while excreting 40 g of urea. Assuming that protein is $16 \% \mathrm{Nby}$ weight and that its metabolism yields $18 \mathrm{kJ} \cdot \mathrm{g}^{-1},$ what percentage of the student's energy requirement is met by protein?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
05:37

Problem 5

Production of the enzymes that catalyze the reactions of the urea cycle can increase or decrease according to the metabolic needs of the organism. High levels of these enzymes are associated with high-protein diets as well as starvation. Explain this apparent paradox.

Rabeya Zahid
Rabeya Zahid
Numerade Educator
06:55

Problem 6

Helicobacter pylori, the bacterium responsible for gastric ulcers, can survive in the stomach (where the pH is as low as 1.5 ) in part because it synthesizes large amounts of the enzyme urease.
(a) Write the reaction for urea hydrolysis by urease.
(b) Explain why this reaction could help establish a more hospitable environment for $H .$ pylori, which tolerates acid but prefers to grow at near-neutral pH.

Sana Riaz
Sana Riaz
Numerade Educator
04:44

Problem 7

Why are phenylketonurics warned against eating products containing the artificial sweetener aspartame (NutraSweet; chemical name L-aspartyl-L-phenylalanine methyl ester)?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
15:06

Problem 8

Demonstrate that the synthesis of heme from PBG as labeled in Fig. $26-35$ results in the heme-labeling pattern given in Fig. $26-32$

Susan Hallstrom
Susan Hallstrom
Numerade Educator
05:53

Problem 9

Explain why certain drugs and other chemicals can precipitate an attack of acute intermittent porphyria.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
04:09

Problem 10

Heterozygotes for erythropoietic protoporphyria show only 20 to $30 \%$ residual ferrochelatase activity rather than the
$50 \%$ that is normally expected for an autosomal dominant inherited disease. Provide a plausible explanation for this observation.

Sana Riaz
Sana Riaz
Numerade Educator
02:55

Problem 11

One of the symptoms of kwashiorkor, the dietary protein deficiency disease in children, is the depigmentation of the skin and hair. Explain the biochemical basis of this symptom.

Sana Riaz
Sana Riaz
Numerade Educator
02:24

Problem 12

What are the metabolic consequences of a defective uridylylremoving enzyme in $E .$ coli?

R N
R N
Numerade Educator
15:33

Problem 13

Figure $26-60,$ Reaction $9,$ indicates that methionine is synthesized in microorganisms by the methylation of homocysteine in a reaction in which $N^{5}$ -methyl-THF is the methyl donor. Yet, in the breakdown of methionine (Fig. $26-18$ ), its demethylation occurs in three steps in which SAM is an intermediate. Discuss why this reaction does not occur via the simpler one-step reversal of the methylation reaction.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
07:28

Problem 14

In the glucose-alanine cycle (Fig. 26-3), glycolytically derived pyruvate is transaminated to alanine and exported to the liver for conversion to glucose and return to the cell. Explain how a muscle cell is able to participate in this cycle under anaerobic (vigorously contracting) conditions. (Hint: The breakdown of many amino acids yields $\mathrm{NH}_{3}$.)

Susan Hallstrom
Susan Hallstrom
Numerade Educator
09:00

Problem 15

Draw the activated intermediates involved in (a) glutamine and
(b) asparagine biosynthesis from glutamate and aspartate, respectively.
(c) Provide an example of another metabolic activation of a carboxylic acid group analogous to each of these reactions.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:04

Problem 16

The $\alpha_{2} \beta_{2}$ tetramer of tryptophan synthase catalyzes the PLP-dependent reaction of indole-3-glycerol phosphate and serine to form tryptophan (Fig. 26-63, Reactions 5 and 6). Draw the chemical reactions involved in this synthesis, including the participation of $\mathrm{PLP}$, and use curved arrows to show the flow of electrons. What role does PLP play in the reaction?

Sana Riaz
Sana Riaz
Numerade Educator
01:38

Problem 17

Suggest a reason why the nitrogen-fixing heterocysts of cyanobacteria have lost Photosystem II but retain Photosystem I..

James Kiss
James Kiss
Numerade Educator