Molecular biochem

Question 1

What pathway is CPS I (carbamoyl-phosphate-synthetase) used in? Location? Nitrogen source

Answer 1

Urea cycle. Mitochondria. Ammonia

Question 2

What pathway is CPS II (carbamoyl-phosphate-synthetase) used in? Location? Nitrogen source

Answer 2

Pyrimidine synthesis (rate limiting step). Cytosol. Glutamine.

Question 3

What is the rate limiting step in purine synthesis?

Answer 3

PRPP amidotransferase

Question 4

What is the rate limiting step in pyrimidine synthesis?

Answer 4

CPS II (carbamoyl-phosphate-synthetase)

Question 5

**What are the sources of carbons in the formation of purines?

Answer 5

Glycine, CO2, Tetrahydrofolate. Aspartate and glutamine are also essential (donate nitrogens)

Question 6

**What are the carbon sources in pyrimidine synthesis?

Answer 6

Aspartate and CO2. (CO2 and glutamine form carbamoyl phosphate).

Question 7

What accounts for the positive charge of histones.

Answer 7

Lysine and Arginine

Question 8

What accounts for the negative charge of DNA

Answer 8

phosphate groups on nucleoTides (vs nucleosides which are simply base + ribose)

Question 9

How many adenine residues are found in a molecule of DNA if one strand contains A =2000, G = 500, C= 1500, and T= 1000.

Answer 9

3000 (2000 on this side, plus 1000 on the other since there are 1000 T’s)

Question 10

What strand of DNA nucleotides opposes the strand 5’ ATTGCGTA 3’

Answer 10

TACGCAAT (3’ TAACGCAT 5’). MUST MAKE SURE TO WRITE IT 5’ ->3’

Question 11

Which med? Inhibits ribonucleotide reductase

Answer 11

Hydroxyurea

Question 12

Which med? Inhibits dihydrofolate reductase

Answer 12

Methotrexate and trimethoprime

Question 13

Which med? inhibits PRPP synthetase

Answer 13

6-MP

Question 14

Which med? inhibits inosine monophosphate dehydrogenase

Answer 14

Mycophenylate

Question 15

Which med? inhibits thymidylate synthase

Answer 15

5-FU

Question 16

What are the characteristic features of orotic aciduria?

Answer 16

Orotic acid in the urine. Megaloblastic anemia that is not correctable with vitamin B12 or folate. Failure to thrive. No elevated blood levels of ammonia. (**Autosomal recessive, UMP synthase defect -> accumulation of orotic acid)

Question 17

**How does UV light damage DNA?

Answer 17

Causes a thymine-thymine bond on the same strand of DNA (thymine dimer). Not on complementary strands.

Question 18

Which eukaryotic DNA polymerase replicates lagging strand and synthesizes RNA primer?

Answer 18

DNA polymerase alpha

Question 19

Which eukaryotic DNA polymerase repairs DNA?

Answer 19

DNA polymerase beta/ epsilon

Question 20

Which eukaryotic DNA polymerase replicates mitochondrial DNA?

Answer 20

DNA polymerase gamma

Question 21

Which eukaryotic DNA polymerase replicates leading strand DNA?

Answer 21

DNA polymerase delta

Question 22

Which antibiotic(s)? Inhibits the 50s peptidyltransferase

Answer 22

Chloramphenicol and streptogramins

Question 23

Which antibiotic(s)? binds 50s blocking translocation

Answer 23

Macrolides, linezolide

Question 24

Which antibiotic(s)? bind 30s, preventing attachment of the tRNA

Answer 24

Tetracyclines

Question 25

Which antibiotic(s)? inhibits prokaryotic RNA polymerase

Answer 25

Rifampin

Question 26

Which antibiotic(s)? inhibits prokaryotic topoisomerase

Answer 26

Fluoroquinilones

Question 27

Which antibiotic(s)? inhibits prokaryotic dihydrofolate reductase

Answer 27

Trimethoprim (methotrexate does also but is a immunosuppresent/ anticancer drug)

Question 28

What are three different mechanisms cells employ to break down proteins

Answer 28

1. Ubiquitin tagging with ubiquitin protein ligase degradation 2. Lysosome 3. Ca++ enzyme

Question 29

What enzyme catalyzes peptide bond formation during protein synthesis?

Answer 29

Peptidyl transferase (ribozyme = 23s rRNA)

Question 30

What enzyme matches amino acids to tRNA?

Answer 30

Aminoacyle-tRNA synthetase

Question 31

What are the mRNA stop codons?

Answer 31

UGA, UAA, UAG (You go away, you are away, your are gone)

Question 32

what are the different RNA polymerases in eukaryotes?

Answer 32

RNA polymerase I -> codes for rRNA RNA polymerase II -> transcribes mRNA RNA polymerase III -> codes for tRNA

Question 33

What amino acid typically has more coding sequences in the mRNA than are represented in the peptide that is created from that mRNA?

Answer 33

Methionine

Question 34

**How is hnRNA processed before it leaves the nucleus

Answer 34

Gets a 5' cap, poly A tail and introns spliced out

Question 35

What is the characteristic sequence of the promotor region? What does a mutation in the sequence cause?

Answer 35

TATA box (-25 nucleotides) and CAAT box (-75 nucleotides). Mutation will decrease amount of gene transcription

Question 36

What enzyme is deficient in Lesch-Nyhan syndrome? Tx?

Answer 36

HGPRT. Allopurinol

Question 37

What structural motifs allow for proteins to bind to DNA?

Answer 37

1. Helix loop helix 2. Helix turn helix 3. Zinc finger 4. Leucine zipper