Molecular biochem

Question 1

nucleasome core

Answer 1

(H2A, H2B, H3, H4) x 2

Question 2

heterochromatin

Answer 2

highly condensed

Question 3

DNA methylation

• what is methylated
• what does it do
• CpG islands?

Answer 3

• cytosine and adenine
• marks old strands
• if methylated –> mutes transcription

Question 4

histone methylation

Answer 4

usually represses transcription … sometimes activates

Question 5

histone acetylation

Answer 5

relaxes DNA coiling –> allows transcription

Question 6

what adds sugar and phosphate to bases?

Answer 6

PRPP synthetase

Question 7

leflunomide inhibits?

Answer 7

dihydroorotate dehydrogenase –> therefore inhibits de novo pyrimidine synthesis

Question 8

mycophenolate and ribavirin inhibit?

Answer 8

IMP dehydrogenase –> inhibits GMP synthesis during de novo purine synthesis

Question 9

hydroxyurea inhibits?

Answer 9

ribonucleotide reductase –> screws up de novo pyrimidine synthesis

Question 10

6-mercaptopurine (6-MP) inhibits?

Answer 10

de novo purine synthesis … stops it right at the beginning

Question 11

5-fluorouracil (5-FU) inhibits?

Answer 11

thymidylate synthase –> decreases dTMP formation –> inhibits de novo pyrimidine synthesis

Question 12

MTX, TMP, pyrimethamine inhibit what?

Answer 12

Dihydrofolate reductase –> decreases DHF conversion to THF which is needed for dTMP formation

Question 13

Lesch Nyhan Syndrome

• cause
• sxs
• tx

Answer 13

• HGPRT def in the purine salvage pathway
• Hyperuricemia; Gout; Pissed off (aggressive and self-mutilating); dysTonia
• allopurinol (xanthine oxidase inhibitor)

Question 14

Adenosine deaminase def

• mechanism
• a/w what condition

Answer 14

can’t shunt adenosine down towards uric acid –> so end up with ATP and dATP excess –> negative feedback that inhibits ribonucleotide reductase –> prevents DNA synthesis

• major cause of AR SCID

Question 15

DNA polymerase III

• which direction synthesis
• which direction proofread

Answer 15

• 5-> 3 synthesis

- 3–> 5 proofreading exonuclease

Question 16

DNA polymerase I

Answer 16

degrades RNA primer using 5–>3 exonuclease and replaces it with DNA

Question 17

missense mutation

Answer 17

NT substitution resulting in a new coded amino acid

Question 18

nonsense mutation

Answer 18

NT substitution resulting in early stop codon

Question 19

single strand DNA repair methods (3)

- a/w what conditions?

Answer 19

1. NT excision repair (def in xeroderma pigmentosum [pyrimidine dimers])
2. base excision repair (imp in repair of toxic/spontaneous deamination)
3. mismatch repair (def in HNPCC)

Question 20

double strand DNA repair method (1)

- what is it mutated in?

Answer 20

nonhomologous end joining (mut in ataxia telengactasia)

Question 21

how many RNA polymerases do Euks have and what do they do

Answer 21

• 3

- Pol I for rRNA, II for mRNA, III for tRNA

Question 22

how many RNA polymerases do Prokes have and what do they do

Answer 22

• 1

- makes all 3 kinds of RNA

Question 23

what end (3 or 5') is AA attached to tRNA
- @ what sequence

Answer 23

3’

CCA (can carry aa’s)

Question 24

Euk ribosomal subunits

Answer 24

40+60 = 80

Question 25

Prok ribosomal units

Answer 25

30+50 = 70

Question 26

6-mercaptopurine and 6-thioguanine are converted to their active metabolites by what

Answer 26

hypoxanthine-guanine phosphoribosyl transferase (HGPRT)

Question 27

what degrades 6-mercaptopurine to inactive metabolite?

Answer 27

xanthine oxidase

Question 28

what is an irreversible inhibitor of adenosine deaminase?

Answer 28

pentostatin

cytotoxic purine analog

Question 29

what’s a cytotoxic purine analog that is resistant to degradation by adenosine deaminase?

Answer 29

cladribine

Question 30

30S unit of Proke ribosome has rRNA strand - what is that piece and its function

Answer 30

16S rRNA

- binds to Shine-Dalgarno sequence

Question 31

23S rRNA
where is it
what does it do

Answer 31

in 50S subunit

peptidyltransferase function - peptide bond during translation