Deck 22: Biosynthesis of Amino Acids, nucleotides, and Related Molecules

Question 1

Glutamine,arginine,and proline:

A)do not have a common precursor.
B)may all be derived from a citric acid cycle intermediate.
C)may all be derived from a Cori cycle intermediate.
D)may all be derived from a glycolytic intermediate.
E)may all be derived from a urea cycle intermediate.

Answer 1

may all be derived from a citric acid cycle intermediate.

Question 2

If glucose labeled with ¹⁴C at C-1 were the starting material for amino acid biosynthesis,the product(s)that would be readily formed is (are):

A)serine labeled at the carboxyl carbon.
B)serine labeled at alpha carbon.
C)serine labeled at the R-group carbon.
D)All of the above
E)None of the above

Answer 2

serine labeled at the R-group carbon.

Question 3

Erythrose 4-phosphate is a precursor of:

A)aspartate.
B)cysteine.
C)phenylalanine.
D)serine.
E)threonine.

Answer 3

phenylalanine.

Question 4

Homoserine is:

A)a precursor of both methionine and threonine.
B)a precursor of serine.
C)derived from homocysteine.
D)derived from serine.
E)derived from threonine.

Question 5

Which of the following is not true about the anammox reaction?

A)Anammox converts ammonia to nitrogen.
B)Anammox is performed by symbiotic bacteria of leguminous plants.
C)Anammox generates the highly reactive molecule hydrazine that is a component of rocket fuel.
D)Anammox occursw anaerobically.
E)The ultimate electron acceptor in anammox is nitrite.

Question 6

The nitrogen atom in the indole ring of tryptophan is derived from which amino acid?

A)Aspartic acid
B)Glutamic acid
C)Glutamine
D)Asparagine
E)Arginine

Question 7

The nitrogen atom in the side chain of lysine is derived from which amino acid?

A)Aspartic acid
B)Glutamic acid
C)Glutamine
D)Asparagine
E)Arginine

Question 8

An important intermediate in the biosynthetic pathway to aromatic amino acids is:

A)benzoic acid.
B)lactate.
C)orotate.
D)shikimate.
E)( $\alpha$ -ketoglutarate.)

Question 9

Which of the following statements about the fixation of atmospheric nitrogen (N₂)into NH₃ by living cells is false?

A)It involves the transfer of eight electrons per mol of N₂.
B)It occurs in certain microorganisms,but not in humans.
C)It requires a source of electrons,normally ferredoxin.
D)It requires one ATP per mol of N₂ fixed.
E)It requires two key protein components,each containing iron.

Question 10

The amino acid __________ and is an intermediate in the biosynthesis of _________.

A)histidine;purines
B)glycine;heme
C)serine;heme
D)serine;sphingosine
E)glutamine;glutathione

Question 11

If a cell were unable to synthesize or obtain tetrahydrofolic acid (H₄ folate),it would probably be deficient in the biosynthesis of:

A)isoleucine.
B)leucine.
C)lysine.
D)methionine.
E)serine.

Question 12

Glutamine synthetase converts _____ to _____ whereas glutamate synthase converts ____ to _____.

A)formate;glutamine;ammonia;glutamate
B)asparagine;glutamine; $\alpha$ -ketoglutarate;glutamate
C)( $\alpha$ -ketoglutarate;glutamine;oxaloacetic acid;glutamate)
D)( $\alpha$ -ketoglutarate;glutamine; $\alpha$ -ketoglutarate;glutamate)
E)glutamate;glutamine; $\alpha$ -ketoglutarate;glutamate

Question 13

Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?

A)Arginase
B)Glutamate dehydrogenase
C)Glutamate synthase
D)Glutamine synthetase
E)Dinitrogenase

Question 14

An amino acid that does not derive its carbon skeleton,at least in part,from $\alpha$ -ketoglutarate is:

A)arginine.
B)glutamate.
C)glutamine.
D)proline.
E)threonine.

Question 15

In which group are all the amino acids closely interrelated metabolically?

A)Arginine,hydroxyproline,and histidine
B)Arginine,tyrosine,and glutamate
C)Glycine,valine,glutamine,and aspartate
D)Ornithine,alanine,glycine,and valine
E)Ornithine,proline,arginine,and glutamate

Question 16

Nonessential amino acids:

A)are amino acids other than those required for
B)are not utilized in mammalian proteins.
C)are synthesized by plants and bacteria,but not by humans.
D)can be synthesized in humans as well as in bacteria.
E)may be substituted with other amino acids in proteins.

Question 17

The enzymatic machinery to fix atmospheric N₂ into NH₄⁺ is:

A)a means of producing ATP when excess N₂ is available.
B)composed of two key proteins,each containing iron.
C)relatively stable when exposed to O₂.
D)specific to plant cells.
E)unaffected by the supply of electrons.

Question 18

Which of the following is not true about glutamine amidotransferases?

A)These enzymes proceed via a covalent intermediate.
B)Ammonia is released into a channel.
C)Glutamate is a product of the reaction.
D)ATP is needed to activate the glutamine.
E)A Cys at the active site is critical for the activity of these enzymes.

Question 19

Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?

A)Dinitrogenase reductase
B)Nitrate reductase
C)Nitrite reductase
D)Nitrile reductase
E)Dinitrogenase

Question 20

An amino acid that does not derive its carbon skeleton,at least in part,from oxaloacetate is:

A)aspartate.
B)lysine.
C)methionine.
D)proline.
E)threonine.

Question 21

Which one of the following statements is true of the biosynthetic pathway for purine nucleotides?

A)CO₂ does not participate in any of the steps in this pathway.
B)Deoxyribonucleotides are formed from 5-phosphodeoxyribosyl 1-pyrophosphate.
C)Inosinate is the purine nucleotide that is the precursor of both adenylate and guanylate.
D)Orotic acid is an essential precursor for purine nucleotides.
E)The amino acid valine is one of the precursors contributing to purine nucleotides.

Question 22

Glutamine is a nitrogen donor in the synthesis of:

A)CTP.
B)dTTP.
C)inosinic acid (IMP).
D)orotate.
E)UMP.

Question 23

A cell that is unable to synthesize or obtain tetrahydrofolic acid (H₄ folate)would probably be deficient in the biosynthesis of:

A)CMP.
B)GMP.
C)orotate.
D)thymidylate (TMP).
E)UMP.

Question 24

An intermediate of purine degradation in humans is:

A)glutamate.
B)NH₄⁺.
C)succinate.
D)urea.
E)uric acid.

Question 25

The amino acid that gives rise to the biological messenger NO is:

A)glutamine.
B)arginine.
C)proline.
D)lysine.
E)histidine.

Question 26

Precursors for the biosynthesis of the pyrimidine ring system include:

A)carbamoyl phosphate and aspartate.
B)glutamate,NH₃,and CO₂.
C)glycine and succinyl-CoA.
D)glycine,glutamine,CO₂,and aspartate.
E)inosine and aspartate.

Question 27

CMP,UMP,and TMP all have ________________ as a common precursor.

A)adenosine
B)aspartate
C)glutamine
D)inosine
E)S-adenosyl methionine

Question 28

The synthesis of purine and pyrimidine nucleotides differ in that:

A)ATP is required in the synthesis of purines but not in the synthesis of pyrimidines.
B)purine biosynthesis starts with the formation of PRPP,whereas pyrimidines incorporate the PRPP near the end of the pathway.
C)purine formation requires a THF derivative,whereas pyrimidine formation does not.
D)pyrimidine biosynthesis is tightly regulated in the cell,whereas purine biosynthesis is not.
E)pyrimidines go through many steps,adding a single carbon or nitrogen each time,whereas the basic skeleton for purines is formed by two main precursors.

Question 29

The ribosyl phosphate moiety needed for the synthesis of orotidylate,inosinate,and guanylate is provided most directly by:

A)5-phosphoribosyl 1-pyrophosphate.
B)adenosine 5'-phosphate.
C)guanosine 5'-phosphate.
D)ribose 5-phosphate.
E)ribulose 5-phosphate.

Question 30

Glutathione is a(n):

A)enzyme essential in the synthesis of glutamate.
B)isomer of oxidized glutamic acid.
C)methyl-group donor in many biosynthetic pathways.
D)product of glutamate and methionine.
E)tripeptide of glycine,glutamate,and cysteine.

Question 31

The most direct precursors of the nitrogens of UMP are:

A)aspartate and carbamoyl phosphate.
B)glutamate and aspartate.
C)glutamate and carbamoyl phosphate.
D)glutamine and aspartate.
E)glutamine and carbamoyl phosphate.

Question 32

De novo purine biosynthesis is distinguished from de novo pyrimidine biosynthesis by:

A)condensation of the completed purine ring with ribose phosphate
B)incorporation of CO₂.
C)inhibition by azaserine (a glutamine analog).
D)participation of aspartate.
E)participation of PRPP (phosphoribosyl pyrophosphate).

Question 33

Which of the following statements is true about gout?

A)Gout is caused by excessive breakdown of pyrimidine nucleotides.
B)Gout can be treated by administration of fluorouracil.
C)Gout is particularly prevalent in patients lacking xanthine oxidase.
D)Gout leads to deposition of sodium urate crystals in the joints.
E)Eating more liver is an effective way to treat the symptoms of gout.

Question 34

The plant hormone indole-3-acetate (auxin)is formed from:

A)arginine.
B)histidine.
C)phenylalanine.
D)threonine.
E)tryptophan.

Question 35

The hormones epinephrine and norepinephrine are derived biosynthetically from:

A)arginine.
B)histidine.
C)isoleucine.
D)tryptophan.
E)tyrosine.

Question 36

l-Dopa is an intermediate in the conversion of:

A)phenylalanine to homogentisic acid.
B)phenylalanine to tyrosine.
C)tyrosine to epinephrine.
D)tyrosine to phenylalanine.
E)tyrosine to phenylpyruvate.

Question 37

Orotic aciduria is an inherited metabolic disease in which orotic acid (orotate)accumulates in the tissues,blood,and urine.The metabolic pathway in which the enzyme defect occurs is:

A)epinephrine synthesis.
B)purine breakdown.
C)purine synthesis.
D)pyrimidine breakdown.
E)pyrimidine synthesis.

Question 38

Which of the following is not true of the reaction catalyzed by ribonucleotide reductase?

A)Glutathione is part of the path of electron transfer.
B)It acts on nucleoside diphosphates.
C)Its mechanism involves formation of a free radical.
D)There is a separate enzyme for each nucleotide (ADP,CDP,GDP,UDP).
E)Thioredoxin acts as an essential electron carrier.

Question 39

Bile pigments are:

A)formed in the degradation of heme.
B)generated by oxidation of sterols.
C)responsible for light reception in the vertebrate eye.
D)secreted from the pancreas
E)the products of purine degradation.

Question 40

Which one of the following statements correctly describes the biosynthetic pathway for purine nucleotides?

A)Purine deoxynucleotides are made by the same path as ribonucleotides,followed by reduction of the ribose moiety.
B)The first enzyme in the path is aspartate transcarbamoylase (ATCase).
C)The nitrogen in the purine base that is bonded to ribose in the nucleotide is derived originally from glycine.
D)The pathway occurs only in plants and bacteria,not in animals.
E)The purine rings are first synthesized,then condensed with ribose phosphate.

Question 41

Describe and contrast,with diagrams,concerted (cumulative)feedback regulation and sequential feedback inhibition.

Question 42

Show the steps by which an intermediate of glycolysis can be converted into serine.

Question 43

Describe two types of regulation of the enzyme glutamine synthetase and explain why the regulation of this enzyme is so complex.

Question 44

Give the overall reaction that results from the combined action of glutamate synthase and glutamine synthetase.

Question 45

In bacteria,the amino acids listed below can be derived directly or indirectly from serine,alanine,aspartate,glutamate,or chorismate.Indicate below which of these "parent" compounds provides the carbon skeleton for each amino acid:
Parent compound
Asparagine __________________
Tryptophan __________________
Glycine __________________
Methionine __________________
Threonine __________________
Cysteine __________________
Proline __________________
Isoleucine __________________
Phenylalanine __________________

Question 46

Show the reaction catalyzed by glycine synthase,indicating the role of any cofactors that participate.

Question 47

Show the biosynthetic pathway for the conversion of a citric acid cycle intermediate into proline.Indicate where any cofactors participate.

Question 48

Which of the following is not a chemotherapeutic drug?

A)Azaserine
B)Allopurinol
C)Fluorouracil
D)Methotrexate
E)Acivicin

Question 49

Draw the structure of 5'-UMP (uridylic acid).Circle those carbon atoms donated by atoms derived from aspartate.

Question 50

Give the equations for the two-step reaction sequence catalyzed by glutamine synthetase.

Question 51

Trace the path of nitrogen from atmospheric N₂ into glutamate.Name the intermediates (no structures necessary)and enzymes,and show any coenzymes involved.

Question 52

Draw the structure of 5'-GMP.Indicate with an arrow the atom(s)derived from glutamine's amide group(s).

Question 53

Show how you can form $\delta$ -aminolevulinate from either glycine and succinyl-CoA or from glutamate.

Question 54

Describe the pathway by which GMP is converted into GTP;show the co-substrates that are involved and name the enzymes.

Question 55

Give the name and structure of the glycolytic or citric acid cycle intermediate that has the same carbon skeleton as (a)alanine, (b)glutamate, (c)aspartate.

Question 56

Match the signaling molecule with its amino acid precursor (a given precursor may be used more than once or not at all):

Question 57

Show the two-step reaction catalyzed by tryptophan synthetase.

Question 58

Draw the structure of 5'AMP.What is the first "committed" step in the biosynthetic sequence that leads to 5'AMP? How is this step regulated?

Question 59

Why is it necessary to have protein in our (human)diets?

Question 60

An animal cell is capable of converting alanine into serine.What is the shortest pathway using known enzymes by which this conversion could be accomplished? Show intermediates and cofactors;no enzyme names are required.(Hint: The first step is removal of the nitrogen by transamination. )

Question 61

Explain how lack of adenosine deaminase leads to a 100-fold increase in dATP,yet also causes a deficiency in dNTPs required for replication of T-cells and B-cells required for a functioning immune system.

Question 62

Diagram the biosynthetic pathway from UMP to dTTP.Use abbreviations (e.g. ,UMP),not complete structures,and indicate where any co-substrates participate.

Question 63

Azaserine is a structural analog of glutamine.It is a competitive inhibitor of many enzymes that use glutamine as substrates.Name)three biosynthetic products whose synthesis you would expect to be inhibited by azaserine.Do you think that eating azaserine would be immediately fatal? Why or why not?

Question 64

Show the reaction catalyzed by thymidylate synthase and explain with a simple diagram how the chemotherapeutic agents fluorouracil and methotrexate inhibit the synthesis of dTMP.