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Flashcards in Biochemistry Deck (293)
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31

Allopurinol mechanism

inhibits xanthine oxidase (converts xanthine --> uric acid)

32

Origin of Replication

sequence of genome where DNA replication begins; single in prokaryotes, multiple in eukaryotes

33

Helicase

unwinds DNA template at replication fork

34

SSBPs (single-stranded binding proteins)

prevent strands from reannealing (stabilize unwound DNA)

35

Fluoroquinolones mechanism?

inhibit DNA gyrase (prokaryotic topoisomerase II)

36

Etoposide mechanism?

Inhibits human tropoisomerase (anti-cancer drug)

37

DNA topoisomerases

create a nick in the helix to relieve supercoils created during replication

38

DNA polymerase III

-Prokaryotic only
-Elongates leading strand by adding deoxynucleotides to the 3' end.
-Elongates lagging strand until it reaches the primer of the preceding fragment
-3'-->5' exonuclease activity "proofreads" each added nucleotide.
*SO: 5'-->3' synthesis; 3'-->5' proofreading exonuclease

39

DNA polymerase I

Prokaryotic only
-Degrades RNA primer and fills in the gap with DNA (excision repair)
*SO:excises RNA primer with 5'-->3' exonuclease

40

Telomerase

adds DNA to 3' ends of chromosomes to avoid loss of genetic material with each duplication

41

anti-topoisomerase antibody

anti-SCL70 - in diffuse scleroderma

42

Nucleotide Excision Repair

-repair for small areas of damage
-mutated in xeroderma pigmentosum (can't repair thymine dimers after UV light exposure)
-thymine dimers from UV light are usually repaired by NER

43

Base Excision Repair

-repair 1 damaged base

44

Mismatch Repair

unmethylated, newly synthesized string is recognized, mismatched nucleotides removed, and gap is filled and reasealed
-mutated in HNPCC (hereditary nonpolyposis colorectal cancer)

45

Nonhomologous end joining (type of double strand repair)

-mutated in ataxia telangiectasia
-brings together 2 ends of DNA fragments

46

-most abundant type of RNA?
-longest type?
-smallest type?

"rampant, massive, tiny"
rRNA = most abundant
mRNA = longest
tRNA = smallest

47

mRNA stop codons

-UGA (u go away)
-UAA (u are away)
-UAG (u are gone)

48

Promoter

site where RNA polymerase and other transciption factors bind to DNA
-located 25 (TATA or Hogness box) or 70 (CAAT box) bases upstream from their genes

49

Enhancers and Silencers

Enhancers = stretch of DNA that binds transcription factors
Silencers = where negative regulators (repressors) bind
*Both can be located anywhere upstream, downstream, or even within transcribed gene

50

Eukaryotic RNA Polymerases I, II, III

RNA pol I: makes rRNA
RNA pol II: makes mRNA
RNA pol III: makes tRNA

51

Prokaryotic RNA polymerase

only 1 RNA polymerase --> makes all 3 kinds of RNA

52

Rifampin inhibits?

inhibits prokaryotic RNA polymerase

53

Where are rRNA, mRNA, tRNA synthesized?

rRNA --> synthesized in nucleolus
mRNA and tRNA --> synthesized in nucleoplasm

54

After transcription, processing of the pre-mRNA in the nucleus:

1) Capping on 5'-end
2) Polyadenylation on 3' end (poly-A tail)
3) splicing out of introns by the spliceosome (so, introns stay in nucleus, exons leave nucleus, form mRNA)

55

antibodies to spliceosomal snRNPs?

Lupus pts

56

Effect of glucose on the lac operon?

in presence of glucose: glucose inhibits cAMP, so get decreased cAMP --> decreased CAP (activator protei) --> inhibition of lac operon
So:
-if have glucose --> lac operon is off
-if not lactose --> lac operon is off
-if no glucose, but have lactose --> lac operon is ON!

57

Aminoacyl-tRNA synthetase: what does it do and where does it act?

works at the 3'-OH-end of the tRNA; charges the amino acid onto the tRNA molecule
-uses ATP

58

Tetracyclines mechanism

Tetracyclines bind 30S subunit, preventing attachment of aminoacyl-tRNA

59

Steps of Elongation in protein synthesis:

1) aminoacyl-tRNA binds A site
2) ribosomal rRNA ("ribozyme" = peptidyl transferase) catalyzes peptide bond formation; transfers growing polypeptide to amino acid in A site
3) Ribosome advance 3 nucleotides toward 3' end of RNA, moving peptidyl RNA to P site (translocation)

APE:
A site: incoming Aminoacyl-tRNA
P site: accommodates growing Peptide
E site: holds Empty tRNA as it Exits

60

Aminoglycosides mechansim:

bind 30S on prokaryotic ribosome, and inhibit formation of the initiation complex and cause misreading of mRNA