Qs bank for 1st midterm (P.3)

Question 1

The conversion of cholesterol to pregnenolone is a common reaction in the synthesis of adrenal steroid hormones. Which statements are true for the enzyme catalyzing this reaction?

Select one or more:
a. The enzyme uses biotin as a prosthetic group, which temporarily binds the side chain of cholesterol
b. The enzyme is called ``side-chain cleavage enzyme’’, and is a member of the family of cytochrom P450 isoenzymes
c. The enzyme is localized to the cytosol, where it can easily access its substrate, cholesterol
d. Cholesterol needs to be transported into the mitochondria for the reaction to take place
e. The complete deficiency of this enzyme is lethal

Answer 1

b. The enzyme is called ``side-chain cleavage enzyme’’, and is a member of the family of cytochrom P450 isoenzymes
d. Cholesterol needs to be transported into the mitochondria for the reaction to take place
e. The complete deficiency of this enzyme is lethal

Question 2

De novo synthesis of purine nucleotides utilizes:

Select one or more:
a. glutamine.
b. components of the tetrahydrofolate one-carbon pool.
c. aspartate.
d. glycine.

Answer 2

All of them

Question 3

What is the role of StAR (Steroidogenic Acute Regulatory Protein) in the synthesis of steroid hormones?

Select one or more:
a. It is a protein required for the transport of cholesterol from the cytosol into the mitochondria
b. Congenital lipoid adrenal hyperplasia is a lethal disease, where the mutations are localized to the StAR gene
c. It is a protein required for the transport of cholesterol from the mitochondria to the cytosol, where cholesterol can be converted to pregnenolone
d. In the adrenal cortex ACTH induces the synthesis of StAR, which is necessary for cortisol production
e. In the adrenal cortex angiotensin II induces the synthesis of StAR, which is necessary for aldosterone production

Answer 3

a. It is a protein required for the transport of cholesterol from the cytosol into the mitochondria
b. Congenital lipoid adrenal hyperplasia is a lethal disease, where the mutations are localized to the StAR gene
d. In the adrenal cortex ACTH induces the synthesis of StAR, which is necessary for cortisol production
e. In the adrenal cortex angiotensin II induces the synthesis of StAR, which is necessary for aldosterone production

Question 4

Phosphoribosyl pyrophosphate is required for:

Select one or more:
a. the salvage of adenine
b. the salvage of uridine
c. conversion of purines to uric acid
d. de novo synthesis of purine nucleotides

Answer 4

a. the salvage of adenine
d. de novo synthesis of purine nucleotides

Question 5

Select the cytochrom P450 isoenzymes!

Select one or more:
a. Side chain cleavage enzyme
b. 21-Hydroxylase
c. 11beta-hydroxy-steroid dehydrogenase
d. 17-Hydroxylase
e. 17-hydroxy-steroid dehydrogenase

Answer 5

a. Side chain cleavage enzyme
b. 21-Hydroxylase
d. 17-Hydroxylase

Question 6

Hypoxanthine-guanine phosphoribosyltransferase is an enzyme:

Select one:
a. for conversion of hypoxanthine to guanine
b. for conversion of guanine to hypoxanthine
c. required to convert hypoxanthine and guanine to urate
d. participating in the synthesis of the purine ring
e. required for the salvage of purine bases

Answer 6

e. required for the salvage of purine bases

Question 7

Select the correct statements regarding steroid hormone synthesis in the adrenal gland!

Select one or more:
a. Aldosterone is produced in the zona fasciculata cells
b. Cortisol is produced in the zona fasciculata cells
c. Testosterone is produced from estradiol by the aromatase enzyme
d. The major products in the zona glomerulosa cells are the weak androgens
e. The three layers of the adrenal cortex are specialized for the production of mineralocorticoids, glucocorticoids and estrogens

Answer 7

b. Cortisol is produced in the zona fasciculata cells

Question 8

In tissues where the de novo purine synthesis is not active, adenine nucleotides could be supplied by:

Select one or more:
a. adenine phosphoribosyl transferase
b. ATP uptake from the blood
c. nucleoside phosphorylase
d. hypoxanthine-guanine phosphorybosyl transferase

Answer 8

a. adenine phosphoribosyl transferase
d. hypoxanthine-guanine phosphorybosyl transferase

Question 9

Thioredoxin is involved in the conversion of:

Select one:
a. hypoxantin to ATP.
b. dUMP to dTMP.
c. UTP to CTP.
d. hypoxanthine and guanine to urate
e. ribonucleotides to deoxyribonucleotides

Answer 9

e. ribonucleotides to deoxyribonucleotides

Question 10

What are the signs of aldosterone deficiency?

Select one or more:
a. hypertension (elevated blood pressure)
b. salt loss and dehydration
c. elevated K+ concentration in blood
d. loss of K+ with the urine
e. red bumps on the toes

Answer 10

b. salt loss and dehydration
c. elevated K+ concentration in blood

Question 11

What is the role of the 11beta-hydroxysteroid dehydrogenase enzyme in the mineralocorticoid target cells?

Select one:
a. The enzyme inactivates cortisol
b. The enzyme activates aldosterone
c. The enzyme inactivates DOC (11-deoxycorticosterone)
d. The enzyme activates DOC (11-deoxycorticosterone)
e. The enzyme activates corticosterone

Answer 11

a. The enzyme inactivates cortisol

Question 12

Select the correct order of the enzymes in the de novo synthesis of orotic acid:

Select one:
a. Carbamoyl-phosphate synthetase/Asp transcarbamoylase/Dihydroorotase/Dihydroorotate dehydrogenase Dihydroorotase
Dihydroorotase
b. Dihydroorotase/Carbamoyl-phosphate synthetase/Asp transcarbamoylase/Dihydroorotate dehydrogenase
c. Asp transcarbamoylase/Carbamoyl-phosphate synthetase/Dihydroorotase/Dihydroorotate dehydrogenase
d. Dihydroorotase/Dihydroorotate dehydrogenase/Asp transcarbamoylase/Carbamoyl-phosphate synthetase/

Answer 12

a. Carbamoyl-phosphate synthetase/Asp transcarbamoylase/Dihydroorotase/Dihydroorotate dehydrogenase Dihydroorotase

Question 13

What are the effects of aldosterone?

Select one or more:
a. Increases Na+-reabsorption in the kidney
b. Increases K+-excretion in the kidney
c. Promotes salt and water retention
d. Promotes salt and water loss
e. Induces the gene expression of Na+/K+-ATPase, as well as Na+-, and K+- channels in the kidney tubular cells

Answer 13

a. Increases Na+-reabsorption in the kidney
b. Increases K+-excretion in the kidney
c. Promotes salt and water retention
e. Induces the gene expression of Na+/K+-ATPase, as well as Na+-, and K+- channels in the kidney tubular cells

Question 14

The formation of dATP occurs primarily by:

Select one:
a. salvaging deoxyadenylate by a phosphoribosyltransferase
b. salvaging deoxyadenosine by a phosphoribosyltransferase.
c. converting ATP to dATP using NADH.
d. converting ADP to dADP using thioredoxin.
e. converting dIMP to dAMP using 5,10-methylene THF

Answer 14

d. converting ADP to dADP using thioredoxin.

Question 15

Which of the following reactions will be inhibited by dihydrofolate analogues, such as methotrexates:

Select one or more:
a. de novo synthesis of UMP
b. conversion of dUMP to dTMP.
c. conversion of IMP to GMP
d. de novo synthesis of IMP

Answer 15

b. conversion of dUMP to dTMP.
d. de novo synthesis of IMP

Question 16

What are the correct statements regarding cortisol synthesis?

Select one or more:
a. Cortisol is synthesized exclusively in the zona glomerulosa of the adrenal cortex
b. Cortisol is synthesized in the adrenal medulla
c. Cortisol synthesis does not require the action of 17-hydroxylase
d. The last step of cortisol synthesis is catalyzed by 11-hydroxylase
e. Cortisol is synthesized from cholesterol

Answer 16

d. The last step of cortisol synthesis is catalyzed by 11-hydroxylase
e. Cortisol is synthesized from cholesterol

Question 17

Which enzymes are not required for the synthesis of estrogens starting from cholesterol?

Select one or more:
a. 17-hydroxylase
b. 21-hydroxylase
c. 11-hydroxylase
d. aromatase
e. side chain cleavage enzyme

Answer 17

b. 21-hydroxylase
c. 11-hydroxylase

Question 18

Aspartate is involved as a N-donor in:

Select one or more:
a. conversion of UTP to CTP.
b. synthesis of AMP from IMP
c. synthesis of GMP from IMP
d. de novo synthesis of IMP

Answer 18

b. synthesis of AMP from IMP
d. de novo synthesis of IMP

Question 19

Select the correct statements regarding the production of female sex steroids!

Select one or more:
a. The major site of estrogen production is the adrenal cortex
b. Testosterone is converted to estradiol by aromatase, a cytochrome P450 isoenzyme
c. The ovaries produce estradiol and progesterone
d. In the placenta estradiol is synthesized from the weak androgen, DHEA provided by the maternal or fetal adrenal gland
e. In the placenta estradiol is synthesized from LDL-cholesterol

Answer 19

b. Testosterone is converted to estradiol by aromatase, a cytochrome P450 isoenzyme
c. The ovaries produce estradiol and progesterone
d. In the placenta estradiol is synthesized from the weak androgen, DHEA provided by the maternal or fetal adrenal gland

Question 20

If a cell has an adequate supply of adenine nucleotides but requires more guanine nucleotides:

Select one or more:
a. Glutamine-PRPP amidotransferase will not be fully inhibited.
b. AMP will be a feedback inhibitor of the condensation of IMP with aspartate.
c. ATP will stimulate the production of GMP from IMP.
d. ATP will inhibit IMP dehydrogenase.

Answer 20

a. Glutamine-PRPP amidotransferase will not be fully inhibited.
b. AMP will be a feedback inhibitor of the condensation of IMP with aspartate.
c. ATP will stimulate the production of GMP from IMP.

Question 21

Select the correct statements regarding the production and inactivation of sex steroids!

Select one or more:
a. Leydig cells produce testosterone
b. Testosterone can be reduced to dihydrotestosterone by a cytochrome P450 isoenzyme
c. In the ovaries granulosa cells produce progesterone only in the luteal phase, after ovulation
d. In the ovaries two cell types, the granulosa cell and the theca interna cell have to cooperate for the production of estradiol
e. In the placenta the maternal steroid hormones are inactivated by a cytochrom P450 isoenzyme

Answer 21

a. Leydig cells produce testosterone
c. In the ovaries granulosa cells produce progesterone only in the luteal phase, after ovulation
d. In the ovaries two cell types, the granulosa cell and the theca interna cell have to cooperate for the production of estradiol

Question 22

The lipid that level elevates in the outer leaflet during apoptosis or platelet activation is

Select one:
a. Phosphatydilcholine
b. Cholesterol
c. Phosphatydilserine
d. Sphingomelin

Answer 22

c. Phosphatydilserine

Question 23

What is the role of nucleotides?
Select one or more:

a. Hydrolysis of PP bound to ATP to drive reactions that require an input of energy
b. Building blocks of DNA and RNA
c. Component of coenzymes
d. Second messengers
e. Allosteric effectors of metabolic processes

Answer 23

All are correct

Question 24

Which of the following statements are valid, if hypoxanthine-guanine phosphoribosyl transferase is deficient?

Select one or more:
a. Hypoxanthine is not converted to IMP
b. Hypoxanthine is converted to CMP
c. Guanine is not converted to GMP
d. De novo purine nucleotide synthesis is enhanced
e. Hyperuricaemia develops

Answer 24

a. Hypoxanthine is not converted to IMP
c. Guanine is not converted to GMP
d. De novo purine nucleotide synthesis is enhanced
Hyperuricaemia develops

Question 25

Which of the following statements are valid for the salvage reactions of purine and pyrimidine nucleotides?

Select one or more:
a. Mononucleotides are formed from free bases by phosphoribosylation
b. De novo nucleotide synthesis is inhibited
c. Purine and pyrimidine bases are utilized
d. PRPP is required for the salvage reactions
e. Ribonucleosides are phosphorylated using ATP

Answer 25

All are correct

Question 26

Which of the following states result in hyperuricaemia?

Select one or more:
a. Deficiency of glucose-6-phosphatase
b. Deficiency of hypoxanthine-guanine-phosphoribosyl transferase
c. Cancer patients after chemo and radiation therapy
d. Deficiency of orotate-phosphoribosyl transferase
e. Deficiency of PRPP-amidotransferase

Answer 26

a. Deficiency of glucose-6-phosphatase
b. Deficiency of hypoxanthine-guanine-phosphoribosyl transferase
c. Cancer patients after chemo and radiation therapy

Question 27

Which of the following compounds are substrates of ribonucleotide-reductase?

Select one or more:
a. ADP
b. TMP
c. AMP
d. GMP
e. CDP

Answer 27

a. ADP
e. CDP

Question 28

Which of the following compounds provide atoms directly to form the pyrimidine ring?

Select one or more:
a. Carbamoyl phosphate
b. Aspartate
c. Glutamine
d. CO2/ HCO3-
e. Oxalacetate

Answer 28

a. Carbamoyl phosphate
b. Aspartate
c. Glutamine
d. CO2/ HCO3-

Question 29

Which of the following enzymes catalyse salvage reactions in nucleotide metabolism?

Select one or more:
a. Uridine kinase
b. Cytidine kinase
c. Aspartate carbamoyltransferase
d. Hypoxanthine-guanine-phosphoribosyl transferase
e. PRPP-amidotransferase

Answer 29

a. Uridine kinase
b. Cytidine kinase
d. Hypoxanthine-guanine-phosphoribosyl transferase

Question 30

1518. Which of the following enzymes participate in the synthesis of pyrimidine nucleotides?

Select one or more:
a. PRPP synthetase
b. Carbamoyl phosphate synthetase
c. Aspartate carbamoyltransferase
d. Adenylosuccinate transferase
e. Orotate-phosphoribosyltransferase

Answer 30

a. PRPP synthetase
b. Carbamoyl phosphate synthetase
c. Aspartate carbamoyltransferase
e. Orotate-phosphoribosyltransferase

Question 31

Which of the following intermediates are derived from degradation of purine nucleotides?

Select one or more:
a. Hypoxanthine
b. Orotate
c. N-carbamoyl–aminoisobutyrate
d. Xanthine
e. Ribose-1-phosphate

Answer 31

a. Hypoxanthine
d. Xanthine
e. Ribose-1-phosphate

Question 32

Which of the following intermediates provide N atom directly to form nucleotide bases?

Select one or more:
a. Amido group of Gln
b. Amino group of Glu
c. Asp
d. Gly
e. NH3

Answer 32

a. Amido group of Gln
c. Asp
d. Gly

Question 33

Which of the following intermediates provide C atom directly to form nucleotide bases?

Select one or more:
a. One carbon atom units attached to tertrahydrofolate
b. CO2
c. Asp
d. Gly
e. Methyl-cobalamin

Answer 33

a. One carbon atom units attached to tertrahydrofolate
b. CO2
c. Asp
d. Gly

Question 34

Which of the following factors are involved in the overall regulation of de novo purine nucleotide synthesis?

Select one or more:
a. PRPP inhibits phosphoribosylamine synthesis
b. ADP and GDP are inhibitors of PRPP synthetase
c. AMP, IMP and GMP inhibit PRPP-amidotransferase
d. GMP inhibits adenylosuccinate synthetase
e. ATP is a substrate of GMP-synthetase

Answer 34

b. ADP and GDP are inhibitors of PRPP synthetase
c. AMP, IMP and GMP inhibit PRPP-amidotransferase
e. ATP is a substrate of GMP-synthetase

Question 35

Select the enzymes of ``de novo’’ pyrimidine biosynthesis!

Select one or more:
a. Pyrimidine phosphoryl transferase
b. aspartate carbamoyl transferase
c. ornitine carbamoyl transferase
d. CTP synthetase

Answer 35

b. aspartate carbamoyl transferase
d. CTP synthetase

Question 36

Which of the compound(s) below is/are allosteric inhibitor(s) of PRPP amidotransferase?

Select one:
a. ATP
b. IMP
c. PRPP
d. NADH

Answer 36

b. IMP

Question 37

Which of the following chemotherapeutic agents is an inhibitor of dihydrofolate reductase?

Select one:
a. 3-azido-3-deoxythymidine (AZT)
b. 5-fluorouracil (Fura)
c. 6-merkaptopurine (6-MP)
d. Cytosine arabinoside (araC)
e. methotrexate (MTX)

Answer 37

e. methotrexate (MTX)

Question 38

Which pathways require phosphoribosyl pyrophosphate?

Select one or more:
a. de novo'' purine biosynthesis b.de novo’’ pyrimidine biosynthesis
c. Salvage of purine bases
d. Salvage of pyrimidine nucleosides

Answer 38

a. de novo'' purine biosynthesis b.de novo’’ pyrimidine biosynthesis
c. Salvage of purine bases

Question 39

Which conditions could result in hyperuricaemia?

Select one or more:
a. Increased phosphoribosyl pyrophosphate synthesis b. Decreased rate of purine salvage
c. Glucose-6-phosphatase deficiency
d. Elevated levels of AMP

Answer 39

All are correct

Question 40

Select the false statement related to the metabolism of deoxyribinucleotides

Select one:
a. Ribonucleotide reductase is regulated by ATP, dATP, dGTP and dTTP.
b. dUMP is converted to dTMP by thymidylate synthase, using N5N10- methylene H4folate.
c.dTMP can be formed from dCMP by deamination and subsequent methylation.
d. Deoxyribose 1-Phosphate is formed during degradation of deoxynucleosides.
e. ``de novo’’ synthesis uses the deoxy-form of phosphoribosyl pyrophosphate.

Answer 40

e. ``de novo’’ synthesis uses the deoxy-form of phosphoribosyl pyrophosphate.

Question 41

Glutamine is an N donor in the synthesis of:

Select one or more:
a. CTP.
b. inosinic acid (IMP).
c. orotate.
d. UMP

Answer 41

All are correct

Question 42

Which of the following statements is not true of the pathway by which purine nucleotides are synthesized?

Select one:
a. The amino acid glycine is one of the precursors.
b. Inosinate is the purine nucleotide that is the precursor of both adenylate and guanylate.
c. Deoxyribonucleotides are formed from 5-phosphodeoxyribosyl 1- pyrophosphate.
d. CO2 is required for one of the steps in this pathway.

Answer 42

c. Deoxyribonucleotides are formed from 5-phosphodeoxyribosyl 1- pyrophosphate.

Question 43

Which of the following statements correctly describes the pathway by which purine nucleotides are synthesized?

Select one:
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.

Answer 43

a. Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety.

Question 44

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:

Select one:
a. epinephrine synthesis.
b. purine breakdown.
c. purine synthesis.
d. pyrimidine breakdown.
e. pyrimidine synthesis.

Answer 44

e. pyrimidine synthesis.

Question 45

Precursors for the biosynthesis of the pyrimidine ring system include:

Select one:
a. carbamoyl phosphate and aspartate.
b. glutamate, NH3, and CO2.
c. glycine and succinyl-CoA.
d. glycine, glutamine, CO2, and aspartate.

Answer 45

a. carbamoyl phosphate and aspartate.

Question 46

Which two precursors react directly in the synthesis of UMP?

Select one:
a. aspartate and carbamoyl phosphate.
b. glutamate and aspartate.
c. glutamate and carbamoyl phosphate.
d. glutamine and aspartate.
e. glutamine and carbamoyl phosphate.

Answer 46

a. aspartate and carbamoyl phosphate.

Question 47

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

Select one:
a. ribulose 5-phosphate.
b. ribose 5-phosphate.
c. guanosine 5’-phosphate.
d. adenosine 5’-phosphate.
e. 5-phosphoribosyl 1-pyrophosphate.

Answer 47

e. 5-phosphoribosyl 1-pyrophosphate.

Question 48

Deficiency of folic acid affects the biosynthesis of:

Select one:
a. UMP
b. CMP.
c. orotate.
d. thymidylate (TMP).
e. any pyrimidine nucleotide

Answer 48

d. thymidylate (TMP).

Question 49

An intermediate of purine degradation in humans is:

Select one:
a. glutamate.
b. glycine
c. succinate.
d. urea.
e. xanthine

Answer 49

e. xanthine

Question 50

Which of the following enzymes is involved into the pyrimidine de novo synthesis?

Select one:
a. adenine phosphoribosyl transferase
b. cytosine phosphoribosyl transferase
c. Gln phosphorybosyl-pyrophosphate amidotransferase
d. hypoxantin-guanine phosphoribosyl transferase
e. orotic acid phosphoribosyl transferase

Answer 50

e. orotic acid phosphoribosyl transferase

Question 51

What is the correct name of the enzyme converting inosine to hypoxantine?

Select one:
a. hypoxantine phosphorybosyl transferase
b. inosine kinase
c. inosine phosphatase
d. purine nucleoside phosphorylase
e. xantine oxidase

Answer 51

d. purine nucleoside phosphorylase

Question 52

The product of the reaction catalyzed by the thymidylate synthase is …

Select one:
a. TDP
b. thymidine
c. thymine
d. TMP
e. TTP

Answer 52

d. TMP

Question 53

The product of the reaction catalyzed by the adenosine deaminase is …

Select one:
a. adenine
b. hypoxantine
c. IMP
d. inosine
e. urate

Answer 53

d. inosine

Question 54

Which of the following compounds will be reduced by ribonucleotide reductase?

Select one:
a. UTP
b. UMP
c. UDP
d. TMP
e. dUDP

Answer 54

c. UDP

Question 55

Which of the following compounds will be deaminated by cytidylate deaminase?

Select one:
a. dCDP
b. cytidine
c. CTP
d. CMP
e. CDP

Answer 55

d. CMP

Question 56

Which reaction is catalyzed by 5’ nucleotidase?

Select one:
a. dephosphorylation of nucleoside monophosphates
b. dephosphorypation of nucleoside triphosphates
c. phosphorybosyl transfer of purines
d. phosphorylation of nucleosides monophosphates e. removal of a ribose-5-phosphate from nucleotides

Answer 56

a. dephosphorylation of nucleoside monophosphates

Question 57

Identify Compound A

Answer 57

Purine

Question 58

Identify Compound A

Answer 58

Pyrimidine

Question 59

Identify compound A and compound B

Answer 59

compound A is purine, compound B is pyrimidine

Question 60

Examine the figure below. Which statment is TRUE about the biosynthesis of purine and pyrimidine nucleotides?

Select one:
a. 2′dGTP stimualtes 2′dADP synthesis.
b. ATP inhibits 2’CDP synthesis.
c. 2′dGTP exerts a positive feedback for its own synthesis.
d. 2′dTTP inhibits 2′dGDP synthesis.

Answer 60

a. 2′dGTP stimualtes 2′dADP synthesis.

Question 61

Name the source of the carbon atom designated by X.

Select one:
a. respiratory CO2
b. acetyl-CoA
c. another purine base (AMP, GMP)
d. IMP
e. vitamin B12

Answer 61

a. respiratory CO2

Question 62

Name the source of the nitrogen atom designated by X.

Select one:
a. aspartate
b. asparagine
c. arginine
d. lysine
e. N10 -formyltetrahydrofolat

Answer 62

a. aspartate

Question 63

Name the source of the atoms highlighted in blue.

Select one:
a. glycine
b. AMP
c. arginine
d. citrulline
e. urea

Answer 63

a. glycine

Question 64

Name the source of the nitrogen atom designated by X.

Select one:
a. glutamine
b. creatinine
c. carbamide
d. carbamyl phoshpate
e. NO

Answer 64

a. glutamine

Question 65

Name the source of the carbon atom designated by X.

Select one:
a. “1C”-tetrahydrofolate
b. acetyl-CoA
c. SAM
d. Glutamine
e. Arginine

Answer 65

a. “1C”-tetrahydrofolate

Question 66

Name the source of the carbon atom designated by X.

Select one:
a. N5,N10- methenyltetrahydrofolate
b. mycophenolic acid
c. methylhydrofolate
d. azaserine
e. glutamate

Answer 66

a. N5,N10- methenyltetrahydrofolate

Question 67

Each source of the de novo synthesized purine are marked with letters A-F below. Which atoms require folic acid for their presence in the molecule? Find the correct pair.

Select one:
a. E-C
b. A-C
c. F-D
d. B-D
e. A-E

Answer 67

a. E-C