Step1_BioChem

Question 1

[ssDNA Repair] Nucleotiide exision repair

Answer 1

specific endonucleases release the oligonucleotinde -containing damaged bases; DNA polymerase and ligase fill and reseal the gap (respectively)–> Repair BULKY helix distorign lesions

Question 2

[ssDNA Repair] Nucleotiide exision repair - Clinical relevence

Answer 2

Mutated in Xeroderma Pigmentosum - which prevents repair of pyrimidine dimers because of UV light exposure

Question 3

[ssDNA Repair] Base excision repair

Answer 3

Specific glycolases recognize and remove damaged bases, apurinic/apyrimidinic endonucleases cut DNA at both apurininc and apyrimidinic sites - empty sugar remoed – gap filled and resealed

Question 4

[ssDNA Repair] Base excision repair - Clinical relevance

Answer 4

Repair of spontaneous/toxic deamination

Question 5

[ssDNA Repair] Mismatch repair

Answer 5

Newly synthesized strand - recognized - mismatched nucleotides are removed - gap filled and resealed

Question 6

[ssDNA Repair] Mismatch repair - Clinical relevance

Answer 6

Mutated in HNPCC

Question 7

[dsDNA Repair] Nonhomologus end joining

Answer 7

Brings together 2 ends of DNA fragments to repair ds breaks. No requirment for homology

Question 8

[dsDNA Repair] Nonhomologus end joining

Answer 8

Mutatedin ataxia telangiectasia

Question 9

rRNA

Answer 9

most abundant

Question 10

mRNA

Answer 10

longest

Question 11

tRNA

Answer 11

smallest; CCA at the3’ end; anticodon end is opposite the aminoacyl end

Question 12

aminoacyl-tRNA

Answer 12

synthase and binding of charged tRNA to codon –> responsible for accuracy of amino acid selection

Question 13

Tetracyclines

Answer 13

bind 30S subunit –> prevent attachement of aminoacyl-tRNA

Question 14

mRNA Start Codons

Answer 14

AUG (rarely GUG)

Question 15

[mRNA start codon] Eukaryotes

Answer 15

Codes for methionine

Question 16

[mRNA start codon] Prokaryotes

Answer 16

Code for formmymethionine (f-met)

Question 17

mRNA Stop Codons

Answer 17

UGA, UAA, UAG

Question 18

[Eukaryotes] RNA polymerase I

Answer 18

makes rRNA

Question 19

[Eukaryotes] RNA polymerase II

Answer 19

makes mRNA; opens DNA at polymerase site; inhibted by alpha-amanitin (death mushroom)

Question 20

[Eukaryotes] RNA polymerase III

Answer 20

makes tRNA

Question 21

alpha-amanitin [Amanita phallodes - death cap mushroom]

Answer 21

inhibits RNA polymerase II –> severe HEPATOTOXICITY

Question 22

tRNA Wobble

Answer 22

accurate base pairing only required in the first 2 nucleotide positions of an mRNA codon - may differ in the 3rd “wobble” posistion – code for the same tRNA/amino acid (2/2 degeneracy of genetic code)

Question 23

[Protein Synthesis] Initiation

Answer 23

Activated by GTP hydrolysis; initiation factors help assemble 40S ribosomal subunit w/initiator tRNA –> released when mRNA and ribosomal subunit assemble with the complex

Question 24

[Protein Synthesis] Elongation

Answer 24

(1) Aminoacyle -tRNA binds to A site (except for initiator methionine); (2) Ribosomal rRNA (“ribozyme”) - catalyze peptide bond formation –> transfer growing polypeptide to amino acid in A site; (3) Ribososome advances 3 nucleotide toward 3’ end of mRNA, moving peptidyl tRNA to P site (translocation)

Question 25

[Protein Synthesis] Termination

Answer 25

Stop codon is recognized by release factor --> complete protein released frm the ribosome

Question 26

[Abx - Protein synthesis inhibitors] Aminoglycosides

Answer 26

bind 30S and inhibit formation of initation complex and cause misreading of mRNA

Question 27

[Abx - Protein synthesis inhibitors] Tetracyclines

Answer 27

bind 30S and block aminoacyl tRNA from entering the acceptor site

Question 28

[Abx - Protein synthesis inhibitors] Chloramphenicol

Answer 28

binds 50S and inhibits petidyl transferase

Question 29

[Abx - Protein synthesis inhibitors] Macrolides

Answer 29

binds 50S and prevent release of uncharged tRNA after it has donated its amino acid

Question 30

[posttranslational modification] Trimming

Answer 30

Removal of N or C-terminal propeptides from zymogens to generate mature proteins

Question 31

[posttranslational modification] Covalent alterations

Answer 31

P", glycosylation, hydroxylation, methylation, and acetylation

Question 32

[posttranslational modification] Proteasomal degradation

Answer 32

attachment or ubiquitin to defective prteins to tag them for breakdown

Question 33

Drugs that act on Microtubules

Answer 33

Mebendazole/thiabendazole (antihelmenthic); Griseofulvin (antifungal); Vincristinevinblastine (anti-cancer); paclitazel (anti-brest cancer); cholchicine (anti-gout)

Question 34

Chediak-Higashi Syndrome - pathophys

Answer 34

mutation in lysosomal trafficking regulator gene (LYST) - product required for micotuble-dependent sorting of endosomal proteins into late multivesicular endosome

Question 35

Chediak-Higashi Syndrome - clinical

Answer 35

recurrent pyogenic infections, partial albinism, periferal neuropathy