Which of the following amino acids is not contained in glutathione?

1. alanine
2. glycine
3. cysteine
4. glutamate

Which amino acid is a precursor of the free-radical gas NO?

1. glycine
2. alanine
3. arginine
4. aspartate
5. asparagine

In mammals synthesis of porphyrins

1. starts with condensation of succinyl CoA and glycine
2. occurs in mitochondria
3. utilizes gamma-aminolevulinate synthase as the rate-limiting enzyme
4. all of the above
5. none of the above 

Which of the following is NOT produced in heme degradation?

1. CO
2. bilirubin
3. biliverdin
4. porphobilinogen

Uridine is a

1. base found in RNA
2. ribonucleoside
3. deoxyribonucleoside
4. ribonucleotide
5. deoxyribonucleotide

A precursor for both the purine and pyrimidine de novo pathways of synthesis is

1. aspartate
2. carbamoyl phosphate
3. glutamine
4. glycine
5. tetrahydrofolate derivatives

Which of the following statements is NOT true of de novo pyrimidine biosynthesis?

1. the committed step is catalyzed by aspartate transcarbamoylase
2. the ribose is attached to orotate
3. CTP is synthesized by amination of UTP
4. the substrate for carbamoyl phosphate synthetase is ammonia

Which of the following is NOT true of CTP?

1. it is an allosteric activator of aspartate transcarbamoylase
2. it is an allosteric inhibitor of aspartate transcarbamoylase
3. it can activate phosphatidate for memrbane lipid synthesis
4. it can active head groups for membrane lipid synthesis

Which of the following is true of de novo purine biosynthesis?

1. the purine ring system is assembled on ribose-5-phosphate
2. synthesis of GMP from inosinate requires ATP
3. IMP is the common precursor for both AMP and GMP
4. the rate-limiting enzyme is glutamine phosphoribosyl amidotransferase
5. all are true

Urate

1. is the end produce of purine nucleotide catabolism in humans
2. is an efficient scavenger of reactive oxygen species
3. concentration in serum is near its solubility limit
4. in excess causes gout
5. all of the above

Lesch-Nyhan syndrome results from a defect in

1. de novo purine nucletoide biosynthesis
2. de novo pyrimidine nucleotide biosynthesis
3. salvage synthesis of pyrimidine nucleotides
4. adenine phosphoribosyltransferase
5. hypoxanthine-guanine phosphoribosyltransferase

Ribonucleotide reductase

1. has an iron center that ontains ferric ions bridged by sulfur atom
2. requires formation of a tyrosyl radical for activity
3. requires several cysteines at the active site
4. both 1 and 2 are correct
5. both 2 and 3 are correct

Ribonucleotide reductase is an imperfect enzyme in that after completion of a round of catalysis and release of the product it is not able to perform a second round of catalysis until

1. ferrous iron is oxidized to ferric iron
2. regulatory subunits reform the tyrosyl radical
3. cysteinyl disulfide bonds at the active site are reduced
4. the product is removed from thh active site by glutathione
5. the product is removed from the active by a dNDP chaperone

A graduate student has isolated ribonucleotide reductase from E. coli and is assaying its activity. To get maximal production of dGDP, he should include which of the following in his buffer?

1. dATP, GDP, dTTP
2. ATP, dADP, dCTP
3. ATP, GDP, dTTP
4. dATP, ATP, GMP, dCTP
5. ATP, UDP, GDP, CDP

Thymidylate synthase

1. uses dUMP as a substrate
2. transfers a methyl group from S-adenosyl methionine to the substrate
3. can be suicide inhibited by flurodeoxyuridylate
4. both 1 and 2 are correct
5. both 1 and 3 are correct

Methotrexate is a competitive inhibitor of dihydrofolate reductase. Which of the following would be inhibited by methotrexate?

1. synthesis of TMP
2. synthesis of S-adenosyl methionine
3. synthesis of phosphatidyl choline
4. all of the above
5. none of the above

In mammals the enzymes responsible for synthesis of most membrane phospholipids are located

1. in the cytoplasm
2. on the cytosolic side of the ER membrane
3. in the ER lumen
4. on the cytosolic side of Golgi membranes
5. in the Golgi

Uridine is a

1. base found in both DNA and RNA
2. ribonucleoside found in RNA
3. ribonucleotide found in RNA
4. base found in RNA

The nitrogen atom in carbamoyl phosphate synthesized in the cytoplasm is generated by hydrolysis of

1. ammonia
2. glutamate
3. glutamine
4. N-acetylglutamate
5. urea

The enzyme of de novo pyrimidine nucleotide biosynthesis that is inhibited by CTP is

1. carbamoyl phosphate synthetase
2. aspartate transcarbamoylase
3. pyrimidine phosphoribosyl transferse
4. orotidylate decarboxylase

Which of the following donates atoms to both purine and pyrimidine rings in de novo biosynthetic pathways?

1. carbon dioxide
2. aspartate
3. glycine
4. tetrahydrofolate derivatives
5. none of the above

The product of the rate-limiting reaction of purine nucleotide biosynthesis is..

1. PRPP
2. 5-phosphoribosy-1-amine
3. glycinamide ribonucleotide
4. inosinate

The amino acid in the R2 subunit of ribonucleotide reductase that forms a stable radical is

1. cys
2. glu
3. tyr
4. trp
5. thr

The source of the methyl group in thymidylate is 

1. S-adenosyl methionine
2. a tetrahydrofolate derivative
3. ala
4. phe
5. acetate

Fluorodeoxyuridylate is...

1. a competitive inhibitor of thymidylate synthase
2. a competitive inhibitor of dihydrofolate reductase
3. a suicide inhibitor of thymidylate synthase
4. a suicide inhibitor of dihydrofolate reductase
5. a suicide inhibitor of ribonucleotide reductase

Allopurinol is an effective treatment for gout because it inhibits

1. ATCase
2. carbamoyl phosphate synthetase
3. ribonucleotide reductase
4. thymidylate synthase
5. xanthine oxidase

Lesch-Nyhan syndrome results from defects in the 

1. de novo pathway for purine nucleotide synthesis
2. salvage pathway for purine nucleotide synthesis
3. de novo pathway for pyrimidine nucleotide synthesis
4. salvage pathway for pyrimidine nucleotide synthesis
5. purine degradation

In the de novo pathway of phospholipid synthesis _________ is activated. 

1. phosphatidate
2. diacylglycerol
3. the alcohol
4. dihydroxyacetone
5. lysophosphatidate

The nucleoside triphosphate that activates diacylglycerol is 

1. ATP
2. CTP
3. GTP
4. UTP

The donor of the methyl group for synthesis of dTMP is

1. SAM
2. a tetrahydrofolate derivative
3. biotin
4. methyl transferase

A clinically important inhibitor of thymidylate synthase is..

1. allopurinol
2. methotrexate
3. aminopterin
4. fluorodeoxyuridylate
5. trimethoprim

Lesch-Nyhan disease is due to a virtual absence of

1. cytosolic carbamoyl phosphate synthetase
2. HGPRTase
3. aspartate transcarbamoylase
4. PRPP synthetase
5. glutamine phosphoribosyl amidotransferase

Adenosine is

1. a purine base
2. a pyrimidine base
3. a purine ribonucleoside
4. a pyrimidine ribonucleoside
5. a purine ribonucleotide

In de novo synthesis, which of the following does not donate atoms to the pyrimidine ring?

1. bicarbonate
2. tetrahydrofolate
3. glutamine
4. aspartate

Bicarbonate, Glutamine, and Aspartate are substrates for

1. a cytosolic orotidylate decarboxylase
2. a mitochondrial orotidylate decarboxylase
3. an amido transferase
4. a cytosolic carbamoyl phosphate synthetase
5. a mitochondrial carbamoyl phosphate synthetase

Which of the following enzymes is inhibited by CTP?

1. aspartate transcarbamoylase
2. carbamoyl phosphate synthetase
3. orotidylate decarboxylase
4. pyrimidine phosphoribosyltransferase
5. none of the above

aspartate transcarbamoylase

which of the following represents the order of de novo synthesis of pyrimidine nucleotides?

1. orotate --> orotidylate --> CTP -->UTP
2. orotate --> uracil -->cytosine
3. orotate --> orotidylate --> UTP --> CTP
4. orotate --> uridine --> cytidine

The rate-limiting step of de novo purine nucleotide biosynthesis is catalyzed by

1. carbamoyl phosphate synthetase
2. aspartate transcarbamoylase
3. PRPP synthetase
4. glutamine phosphoribsyl amidotransferase
5. IMP synthase

De novo synthesis of AMP and GMP is kept in balance

1. partly because ATP is required for GMP synthesis, and vice versa
2. each end product inhibits the first enzyme unique to its branch
3. because excess AMP can be converted to GMP, and vice versa
4. both 1 and 2 are correct
5. both 2 and 3 are correct

Which of the following are required at the active site of ribonucleotide reductase?

1. two ferric ions bridged by an oxide ion
2. a tyrosyl radical
3. several cysteines
4. all of the above
5. none of the above

Which of the following conditions would favor synthesis of dUDP?

1. dATP bound at the overall activity site
2. ATP bound at the overall activity site
3. high levels of dTTP
4. high levels of dCTP
5. high levels of all four dNTPs

A student is studying an E. coli strain with a temperature-sensitive mutation in the enzyme that converts xanthylate to GMP. At the non-permissive temperature

1. GTP synthesis stops, but ATP synthesis remains the same
2. both ATP and GTP synthesis stops
3. ATP synthesis rates increase slightly and GTP synthesis stops
4. ATP synthesis rates increase 10-fold, and GTP synthesis stops

Which phospholipid below contains 3 methyl groups donated by SAM?

1. phosphatidyl serine
2. phosphatidyl ethanolamine
3. phosphatidyl choline
4. phosphatidyl glycerol

Which phospholipids below can be synthesized by a salvage pathway?

1. phosphatidyl serine and phosphatidyl ethanolamine
2. phosphatidyl ethanolamine and phosphatidyl choline
3. phosphatidyl choline and phosphatidyl serine
4. none of the above

Phosphatidate is a common intermediate in synthesis of triacylglycerols and phospholipids. in phospholipid synthesis, phosphatidate is activated using 

1. ATP
2. CTP
3. GTP
4. UTP

If Lysine 48 of ubiquitin is mutated to an alanine, which of the following would not occur?

1. ubiquitin activation
2. ubiquitin conjugation
3. ligation of ubiquitin to a target protein
4. polyubiquitination

Which of the following can determine whether a protein will be ubiquinated?

1. a destabilizing residue at the N-terminus
2. PEST sequences
3. cyclin destruction boxes
4. all of the above
5. none of the above

Which of the following organisms do not contain ubiquitin?

1. the bacterium E. coli
2. the yeast Saccharomyces cerevisiae
3. the nematode Caenorhabditis elegans
4. the plant Pisum sativum
5. the mammal Homo sapiens

Glutamate dehydrogenase is more active when

1. ADP & GDP levels are high
2. ATP & GTP levels are high
3. it is phosphorylated
4. it is dephosphorylated

Which of the following enzymes does not contain PLP as a prosthetic group?

1. glycogen phosphorylase
2. aspartate transaminase
3. serine dehydratase
4. glutamate dehydrogenase

Mammalian carbamoyl phosphate synthetase requires _____ for activity

1. phosphorylation
2. dephosphorylation
3. N-acetylglutamate
4. all of the above
5. none of the above

The carbon skeleton of which amino acid could still be catabolized if the citric acid cycle was inhibited?

1. aspartate
2. arginine
3. lysine
4. asparagine
5. glutamine

Absence of which enzyme leads to phenylketornuria?

1. glutamate dehydrogenase
2. aspartate transcarbamoylase
3. carbamoyl phosphate synthetase
4. phenylalanine hydroxylase
5. methylmalonyl CoA mutase

If methylmalonyl CoA mutase is defective, which of the following would not be catabolized?

1. the carbon skeleton of methionine
2. the carbon skeleton of alanine
3. odd chain fatty acids (to completion)
4. both 1 and 3 are correct
5. all are correct

Glutamate dehydrogenase is allosterically inhibited by

1. ATP & GTP
2. ADP & GDP
3. AMP & GMP
4. all nucleoside diphosphates

Aminotransferases require the cofactor ____ for catalysis

1. biotin
2. lipoamide
3. pyridoxal phosphate 
4. vitamin B₁₂
5. tetrahydrofolate

The same cofactor required by aminotransferases also is required by

1. serine dehydratase
2. phenylalanine dehydroxylase
3. methylmalonyl CoA mutase
4. all of the above
5. none of the above

Carbamoyl phosphate synthetase is located in the ________ and is stimulated by ________.

1. cytoplasm; ammonium
2. mitochondrion; N-acetylglutamate
3. cytoplasm; arginine
4. mitochondrion; ammonium
5. cytoplasm; glutamine

The carbon skeleton of leucine is degraded to

1. acetyl CoA and acetoacetyl CoA
2. acetyl CoA and oxaloacetate
3. acetoacetyl CoA and pyruvate
4. oxaloacetate and pyruvate
5. fumarate and pyruvate

The carbon skeleton of aspartate can enter the CAC as ______ as a result of transamination or as ______ as a result of urea cycle activity.

1. oxaloacetate; pyruvate
2. oxaloacetate; fumarate
3. succinyl CoA; oxaloacetate
4. fumarate; succinyl CoA
5. pyruvate; alpha-ketoglutarate

Methylmalonyl CoA mutase requires _____ for activity.

1. vitamin B₁₂
2. PLP
3. biotin
4. FAD
5. NADH

Which of the following amino acids are catabolized in skeletal muscle?

1. alanine and serine
2. threonine and serine
3. glutamate and aspartate
4. leucine and valine
5. isoleucine and methionine

Which of the following is not an essential amino acid in humans?

1. trp
2. his
3. lys
4. asn
5. ile

PEP and erythorse-4-phosphate are precursors of 

1. met
2. his
3. trp
4. cys
5. arg

Which step of the activated methyl cycle requires derivatives of folic acid?

1. conversion of methionine to SAM
2. conversion of homocysteine to methionine
3. conversion of SAM to homocysteine
4. conversion of SAM to S-adenosylhomocysteine

The enzymes that synthesize cysteine from homocysteine require ____ for activity.

1. methylcobalamin
2. biotin
3. PLP
4. TPP
5. ascorbate

A researcher has constructed a chimeric gene consisting of teh catalytic domain of 3-phosphoglycerate dehydrogenase and the regulatory domain from threonine deaminase. What will have to bind the chimeric enzyme in order for its activity to be inhibited?

1. ser
2. ile
3. val
4. both ser and ile must bind
5. all must bind

Unda synthase catalyzes the rate-limiting step in the synthesis of both uga and aga. Neither uga nor aga alone inhibit unda synthase, but both together inhibit it completely. From the information given, you can conclude that this is an example of

1. simple feedback inhibition
2. sequential feedback inhibition
3. cumulative feedback inhibition
4. concerted feedback inhibition
5. enzyme multiplicity

How is glutamine synthetase regulated?

1. simple feedback inhibition
2. sequential feedback inhibition
3. cumulative feedback inhibition
4. concerted feedback inhibition
5. enzyme multiplicity

Glutamine synthetase from E. coli is ___ sensitive to feedback inhibition when it is ___.

1. more; adenylylated
2. less; adenylylated
3. more; uridylylated
4. less; uridylylated
5. more; phosphorylated

Which of the following favors conversion of P_D to P_A?

1. high alpha-ketoglutarate
2. high ATP
3. high glutamine
4. all must be high

The amino acid ____ is the precursor of NO.

1. ala
2. arg
3. asn
4. asp
5. gly

Which amino acid is not a constituent of glutathione?

1. ala
2. gly
3. glu
4. cys

In mammals, all of the atoms in heme come from

1. glycine and acetate
2. leucine and glycine
3. acetate and lysine
4. pyruvate and glycine

The rate-limiting enzyme for porphyrin synthesis mammals is ____ which is located in _____.

1. δ-ALA synthase; mitochondrion
2. porphobilinogen deaminase; mitochondrion
3. ferrochetolase; cytoplasm

Biliverdin and bilirubin are 

1. linear tetrapyrroles
2. intermediates in heme synthesis
3. products of heme degradation
4. both 1 and 2 are correct
5. both 1 and 3 are correct

________ can carry one-carbon units in different oxidation states.

1. biotin
2. tetrahydrofolate
3. SAM
4. both 1 and 2 are correct
5. both 2 and 3 are correct

Nitrogen Fixation occurs only in

1. prokaryotes
2. cyanobacteria
3. single-celled organisms
4. multicellular organisms
5. eukaryotes

In the cyanobacterium Nostoc nitrogen fixation occurs in heterocysts which lack

1. any other enzymes
2. PSI
3. PSII
4. rubisco
5. all of the above

Leghemoglobin

1. is found in nodules of legumes
2. is found in legs of prosimians
3. is found in all nitrogen fixing organisms
4. is found in white leghorn chickens

Which nitrogenase converts N₂ to 2 NH₃ _____ molecules of ATP are required

1. 2
2. 4
3. 8
4. 16
5. 32

The electrons required for nitrogen fixation in most organisms are from

1. reduced ferredoxin
2. reduced thioredoxin
3. reduced glutaredoxin
4. reduced glutathione
5. reduced NAD⁺

The nitrogen reduction site of nitrogenase is thought to be 

1. in the 4Fe-3S cluster
2. in the Mo-3Fe-3S cluster
3. in the P cluster
4. the reductase subunits

Which of the following enzymes would play a role in ammonium assimilation only if ammonium levels were very high?

1. glutamine synthetase
2. glutamate synthetase
3. glutamate dehydrogenase
4. transaminases

Which group below consists only of amino acids that are essential in the human diet?

1. ala, trp, thr
2. his, ile, leu
3. pro, ser, met
4. lys, ala, asp
5. glu, gln, thr

Ribose-5-Phosphate is a precursor of the amino acid

1. ala
2. glu
3. his
4. trp
5. phe

The function of the activated methyl cycle is 

1. synthesis of methionine
2. transfer of methyl group from a tetrahydrofolate to SAM
3. degradation of methionine
4. transfer of methyl groups from SAM to a tetrahydrofolate
5. synthesis of cysteine

The non-specific herbicide Roundup targets an enzyme in 

1. the shikimic acid pathway
2. the activated methyl cycle
3. the synthesis of threonine
4. nitrogen fixation

Glutamine synthetase is more active when it is

1. adenylylated 
2. deadenylylated
3. uridylylated
4. deuridylylated
5. phosphorylated

Uridyl transferase is more active when

1. ATP levels are high
2. alpha-ketoglutarate levels are high
3. glutamine levels are high
4. both 1 and 2 are correct
5. both 1 and 3 are correct

The amino acids ola and ina are end-products of a branched pathway and are synthesized from the common precursor zoa. A student is assaying the rate-limiting enzyme for the pathway and finds that neigher ola nor ina has any effect on its activity. However zoa completely inhibits the enzyme's activity. From all this information you can conclude that the regulation of the pathway is by..

1. cumulative feedback inhibition
2. concerted feedback inhibition
3. sequential feedback inhibition
4. enzyme multiplicity
5. all of the above

The pyrimidine ring is synthesized de novo from 

1. carbamoyl phosphate
2. aspartate
3. glutamate
4. both 1 and 2 are correct
5. both 1 and 3 are correct

The rate limiting enzyme for pyrimidine nucleotide biosynthesis is ____ which is stimulated by ____.

1. aspartate transcarbamoylase; ATP
2. aspartate transcarbamoylase; UTP
3. carbamoyl phosphate synthetase; ATP
4. carbamoyl phosphate synthetase; UTP

CTP is formed by

1. amination of UTP
2. deamination of UTP
3. methylation of UTP
4. demethylation of UTP

amination of UTP

Which of the following does not donate atoms used in de novo synthesis of purine nucleotides?

1. asp
2. gln
3. gly
4. CO₂
5. glu

The rate-limiting step in de novo purine nucleotide synthesis is 

1. synthesis of PRPP
2. synthesis of 5-phosphoribosyl-1-amine
3. synthesis of glycinamide ribonucleotide
4. synthesis of formylglycinamide ribonucleotide
5. synthesis of 5-aminoimidazole ribonucleotide

In the absence of GTP,

1. large amounts of AMP would be synthesied by the de novo pathway
2. no AMP would be synthesized by the de novo pathway
3. the rate-limiting enzyme for de novo synthesis would be inhibited.

Ribonucleotide reductase from E. coli

1. is inhibited by binding of dATP at the overall activity site
2. is inhibited by binding of ATP at the overall activity site
3. has a reaction mechanism involving a tyrosyl radical
4. both 1 and 3 are correct
5. both 2 and 3 are correct

Fluorouracil is a suicide inhibitor of the enzyme

1. aspartate transcarbamoylase
2. thymidylate synthase
3. dihydrofolate reductase
4. ribonucleotide reductase
5. xanthine oxidase

Lesch-Nyhan syndrome results from a virtual absence of 

1. thymidylate synthase
2. xanthine oxidase
3. HGPRase
4. adenine phosphoribosyl transferase
5. carbamoylphosphate synthetase

Gout is usually treated by administering allopurinol which is an inhibitor of 

1. xanthine oxidase
2. HGPRase
3. adenine phosphoribosyl transferase
4. thymidylate synthase

Catalysis by both transketolase and transaldolase involves stabilization of carbanionic intermediates. However, transketolase forms a ___ with the substrate while transaldolase forms a _____.

1. TPP carbanion; Schiff base
2. Schiff base; TPP carbanion
3. tyrosine radical; internal aldimine
4. internal aldimine; tyrosine radical
5. catalytic dyad of histidine and cysteine; covalent linkage

Which of the following can carry out nitrogen fixation

1. higher animals
2. higher plants
3. flatworms
4. bacteria
5. all of the above

A researcher has isolated a mutant of clover in which the leghemoglobin gene is disrupted. As a result

1. there will be no nodules
2. nodules will not be pink
3. there will be no nitrogen fixation
4. both 1 and 3 are correct
5. both 2 and 3 are correct

Glutamate dehydrogenase does not usually function in assimilation of ammonium because

1. the reaction it catalyzes will not ever go in both directions
2. it has a low affinity for ammonium
3. it is most active when the energy charge is low
4. both 1 and 2 are correct
5. both 2 and 3 are correct

If Roundup (glyphosate) is added to a culture of E. coli, the culture might survive if procided ____ in the media

1. methionine, cysteine, and folate
2. tryptophan, tyrosine, and phenylalanine
3. chorismate
4. both 1 and 3 are correct
5. both 2 and 3 are correct

If the P subunit is mutated so that UMP cannot attach to it

1. adenylyl transferase will have no activity
2. glutamine synthetase will be more responsive to cumulative feedback inhibition
3. glutamine synthetase will not be adenylylated
4. there will be no efect since the P subunit cannot bind UMP

High levels of which of the following will lead to a more active glutamine synthetase

1. glutamate
2. ATP
3. alpha-ketoglutarate
4. both 1 and 2
5. both 2 and 3

Most organisms capable of forming symbiotic nitrogen fixing associates with plants belonging to the genus

1. Bacillus
2. Escherichia
3. Klebsiella
4. Nostoc
5. Rhizobium

Nitrogenase

1. is destroyed by oxygen
2. is not synthesized in the presence of oxygen
3. is stimulated by nitrogen
4. boath 1 and 2 are correct
5. both 1 and 3 are correct

Some organisms can take up NO₃^- and convert it to NH₃ by the combined activity of nitrate reductase and nitrite reductase. Which of the following organisms cannot do this?

1. bacteria
2. fungi
3. plants
4. algae
5. mammals

Which of the following steps in the activated methyl cycle is catalyzed by an enzyme requiring methylcobalamin for activity?

1. conversion of SAM to S-adenosylhomocysteine
2. converion of S-adenosylhomocysteine to homocysteine
3. conversion of homocysteine to methionine
4. conversion of methionine to SAM
5. nos tep requires methylcobalamin

At which step is a one-carbon group transferred from a tetrahydrofolate derivative to an inermediate in the activated methyl cycle

1. conversion of SAM to S-adenosylhomocysteine
2. converion of S-adenosylhomocysteine to homocysteine
3. conversion of homocysteine to methionine
4. conversion of methionine to SAM
5. nos tep requires methylcobalamin

Which of the following amino acids is a product of the shikimic acid pathway

1. phenylalanine
2. alanine
3. histidine
4. serine
5. arginine

Uga and unda are end products of a branched biosynthetic pathway. A researcher has isolated the enzyme catalyzing the committed step of the pathway and has found that neither uga nor unda alone is capable of inhibiting the enzyme, but both together can completely inhibit its activity. From this you can conclude that

1. regulation is concerted
2. regulation is cumulative
3. regulation is sequential
4. there is enzyme multiplicity
5. uga and unda must bind the same sit on the enzyme

Which amino acid is not normally essential in the human diet, but would be in a person with PKU?

1. phenylalanine
2. tyrosine
3. tryptophan
4. serine
5. threonine

When ____ is covalently linked to glutamine synthetase from E. coli the enzyme is ____ active.

1. AMP; more
2. AMP; less
3. UMP; more
4. UMP; less
5. phosphate; less

In mammals the nitrogen atoms in heme come from

1. succinyl CoA
2. alanine
3. arginine
4. glycine
5. histidine

PRPP is a precursor in the synthesis of

1. purine nucleotides
2. pyrimidine nucleotides
3. histidine
4. all of the above
5. none of the above

The rate-limiting enzyme for purine nucleotide biosynthesis is catalyzed by 

1. aspartate transcarbamoylase
2. carbamoyl phosphate synthetase
3. PRPP synthetase
4. phosphoribosyl amidotransferase
5. inosinat synthetase

The rate-limiting enzyme for purine nucleotide biosynthesis is stimulated by

1. AMP
2. GMP
3. UMP
4. CMP
5. PRPP

The rate-limiting enzyme for pyrimidine nucleotide biosynthesis in E. coli is 

1. carbamoyl phosphate synthetase
2. PRPP synthetase
3. aspartate transcarbamoylase
4. dihydroorotase
5. orotate phosphoribosyl transferase

The activity of the rate-limiting enzyme for pyrimidine nucleotide biosynthesis E. coli is 

1. inhibited by ATP
2. stimulated by GTP
3. inhibited by CTP
4. inhibited by UTP
5. regulated by reversible phosphorylation

inhibited by CTP

(stimulated by ATP)

Synthesis of deoxyribonucleotides requires a stable free radical. Under anaerobic conditions the enzyme that reduces ribonucleotides most likely

1. contains an iron center in which two Fe³⁺ are linked by oxygen
2. uses SAM to form a 5'-deoxyadenosyl radical
3. uses coenzyme B₁₂ to form an adenosyl cobalamin free radical
4. either 1 or 2 is possible
5. either 2 or 3 is possible

When ATP binds the overall activity site of ribonucleotide reductase, activity ___ and synthesis of ___ is favored

1. increases; purine deoxyribonucleotides
2. increases; pyrimidine deoxyribonucleotides
3. decreases; purine deoxyribonucleotides
4. decreases; pyrimidine deoxyribonucleotides
5. there is no effect on the enzyme

Gout is caused by

1. excess production of urate
2. excess production of purine nucleotides
3. excess production of pyrimidine nucleotides
4. excess degradation of pyrimidine nucleotides
5. none of the above

Gout is treate by administering allopurinol which is an inhibitor of 

1. PRPP synthetase
2. amidophosphoribosyl transferase
3. carbamoyl phosphate synthetase
4. aspartate transcarbamoylase
5. xanthine oxidase

Lesch-Nyhan syndrome results from a nearly total absence of 

1. PRPP synthetase
2. xanthine oxidase
3. HGPRase
4. ATCase
5. amidophosphoribosyl transferase

Which deoxyribonucleotide is not synthesized directly by ribonucleotide reductase

1. dADP
2. dGDP
3. dCDP
4. dTDP
5. dUDP

The methyl group added to dUMP to make dTMP comes from

1. SAM
2. a tetrahydrofolate derivative
3. carbon dioxide
4. any of the above
5. none of the above

Fluorodeoxyuridylate is a ____ inhibitor of ____.

1. irreversible; dihydrofolate reductase
2. irreversible; thymidylate synthase
3. competitive; dihydrofolate reductase
4. competitive; thymidylate synthase
5. competitive; tetrahydrofolate synthase

Aminopterin and methotrexate (amethopterin) are ___ inhibotors of ___. 

1. irreversible; dihydrofolate reductase
2. irreversible; thymidylate synthase
3. competitive; dihydrofolate reductase
4. competitive; thymidylate synthase
5. competitive; tetrahydrofolate synthase

Which of the following statements is NOT true of nitrogen fixation?

1. it can occur in some free-living or symbiotic microorganisms
2. it occurs under anaerobic conditions
3. it requires 16 ATP per N₂ conerted to 2NH₃
4. it requires 8 electrons per N₂ to 2 NH₃
5. the electron donor is NADPH

Leghemoglobin

1. protects symbiotic nitrogen fixing bacteroids from oxygen
2. is encoded in the bacterium's genome
3. is encoded in the plant's genome
4. both 1 and 2 are correct
5. both 1 and 3 are correct

If a farmer kills weeds by applying glyphosate (Roundup) he is directly inhibiting the synthesis of 

1. NADPH
2. phe, tyr, and trp
3. lys, arg, and his
4. ala, gly, and ser
5. carbohydrate by the Calvin Cycle

Tetrahydrofolate derivatives can carry 

1. only CH3 groups
2. only HCO3
3. 1-carbon groups of a number of oxidation states

SAM can carry..

1. only CH3 groups
2. only HCO3
3. 1-carbon groups of a number of oxidation states

A patient has high levels of homocysteine in his blood. His physician gives him a shot of Vitamin B6 and the levels of homocysteine return to normal. Which of the enzymes below could have been deficient in the patient?

1. methionine synthase
2. cystathioninase
3. tetrahydrofolate synthase
4. ACC synthase
5. homocysteine methyltransferase

In E. coli, glutamine synthetase is ___ active when it is ___.

1. more; adenylylated
2. less; adenylylated
3. more; phosphorylated
4. less; phosphorylated
5. more; uridylylated

Which of the following is NOT true of uridylyl transferase?

1. it covalently attaches UMP to the P_II (P_D) subunit of adenylyl transferase
2. its activity results in more activity by glutamine synthetase
3. it is activated by alpha-ketoglutarate 
4. it is inhibited by ATP
5. it is inhibited by gln