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1

What is the rate-limiting enzyme in purine synthesis? In pyrimidine synthesis?

purine: glutamine PRPP amidotransferase

pyrimidine: CPS2 (carbamoyl phosphate synthetase 2)

2

What are the sources of carbon in the synthesis of purines? (3) in pyrimidine synthesis? (2)

- purines: CO2, glycine, tetrahydrofolate
- pyrimidines: aspartate, CO2

3

Which medication inhibits each of the following enzymes?
- ribonucleotide reductase

hydroxyurea

4

Which medication inhibits each of the following enzymes? (2)
- dihydrofolate reductase

TMP, methotrexate

5

Which medication inhibits each of the following enzymes?
- thymidylate synthase

5-FU

6

Which medication inhibits each of the following enzymes?
- inosine monophosphate (IMP) dehydrogenase

mycophenolate

7

Which medication inhibits each of the following enzymes?
- PRPP amidotransferase

6-MP
- note this is the rate-limiting enzyme

8

What accounts for the positive charge of histones? What accounts for the negative charge of DNA?

histones: b/c made of lysine and arginine

DNA: negative b/c of phosphate groups

9

How does UV radiation damage DNA?

makes pyrimidine dimers (usually T-T) on the same strand of DNA --> makes "bulky" helix-distorting lesion

need repair via nucleotide excision repair

10

What amino acid is encoded by the most common start codon?

AUG --> methionine

11

What is the diff. b/w an intron and exon?

Intron: non-coding segment of DNA
Exon: coding sequences for specific protein products

12

Production of what enzyme is regulated by the lac operon?

b-galactosidase

13

What two proteins regulate the lac operon?

- CAP
- lac repressor

14

What 2 substrate conditions must be met for the lac genes to be transcribed?

- abundant lactose (removes repressor)
- low glucose (allows CAP to bind)

15

What enzyme matches amino acids to tRNA?

aminoacyl tRNA synthetase

16

What antibiotics are inhibitors of prokaryotic protein synthesis at the 30S ribosomal subunit?

- aminoglycoside
- tetracyclines

17

What antibiotics are inhibitors of prokaryotic protein synthesis at the 50S ribosomal subunit?

- chloramphenicol
- clindamycin
- macrolides
- linezolid

18

What enzymes convert glucose to glucose-6-phosphate?

hexokinase or glucokinase (only in liver and b-cells of pancreas)

19

What is the clinical consequence of a glycolytic enzyme deficiency?

hemolytic anemia

20

What enzymes are responsible for increasing and dereasing the intracellular levels of fructose-2,6-bisphosphate?

PFK-2 (fed): increase level of fructose 2,6-BP
FBPase-2 (fasting): decrease level of fructose 2,6-BP

21

What is the rate limiting enzyme in the glycolytic pathway?

phosphofructokinase-1

22

What irreversible enzymes are involved in gluconeogenesis (4)

1. pyruvate carboxylase (with biotin)
2. PEP carboxylase
3. fructose-1,6-bisphosphatase
4. glucose-6-phosphatase

23

What enzyme catalyzes the rate-limiting step in gluconeogenesis?

fructose-1,6-bisphosphatase

24

What is the rate limiting enzyme for glycogen synthesis? For glycogenolysis?

- glycogen synthase
- glycogen phosphorylase

25

Which enzyme converts G-6-P to glucose?

glucose-6-phosphatase

26

Which glycogen storage disease matches each of the following phrases?
- glycogen phosphorylase deficiency

McArdle

27

Which glycogen storage disease matches each of the following phrases?
- glucose-6-phosphatase

Von Gierke

28

Which glycogen storage disease matches each of the following phrases?
- lactic acidosis, hyperlipidemia, hyperuricemia (gout)

Von Gierke

29

Which glycogen storage disease matches each of the following phrases?
- a-1,6-glucosidase deficiency

cori

30

Which glycogen storage disease matches each of the following phrases?
- a-1,4-glucosidase deficiency

Pompe