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biochem > translation > Flashcards

translation Flashcards

1
Q

the process of protein synthesis is called ____________, and it occurs on an enzyme complex called the ___________.

A

translation; ribosome

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2
Q

codon

A

series of three bases specifying one amino acid in a protein; code read 5’->3’ and protein is synthesized from amino- (N-) to the carboxyl- (C-) terminus

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3
Q

open reading frame (ORF)

A

encodes the primary sequence of only one protein
- begins with start codon (AUG) and ends at a stop codon
- ORF is continuous series of codons
- genetic code is non-overlapping

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3
Q

the code is degenerate which means

A

most amino acids are encoded by more than one codon
- leu, arg, ser have 6 codons each
- met and trp only have 1

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4
Q

mutation

A

accidental change in a DNA sequence. it may affect the sequence of a protein encoded in an mRNA

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5
Q

nonsense mutation

A

introduces a stop codon; normally results in a nonfunctional protein

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6
Q

missense mutation

A

replaces one amino acid codon with another; protein effects depend on many things

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7
Q

silent mutation

A

changes the DNA sequence without altering the encoded protein

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8
Q

frameshift mutations

A

caused by an insertion or a deletion within a coding sequence, but the change is not a multiple of 3 bases
- often leads to an early stop codon truncating a protein
- mutations that affect RNA splicing often generate frameshifts

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9
Q

what is the most frequent mutation associated with cystic fibrosis?

A

an in-frame deletion of UUC (phe) codon in CFTR

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10
Q

_______ deliver aminos acids to the ribosome
- cloverleaf secondary structure
- many modified bases
- have AAs bound at 3’ end

A

tRNAs

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11
Q

the primary determinants for amino acid selection are _______________________________.
- a tRNA _______ base pairs to a mRNA codon in an antiparallel orientation.

A

bases #1 and #2 of the mRNA codon; anticodon

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12
Q

the third base of many codons pairs loosely, or wobbles, with the corresponding base of its anticodon. this base is known as the ______________

A

wobble base

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13
Q

tRNAs can bind to multiple different codons that encode an amino acid because…

A

of the leniency at the wobble position
- 32 tRNAs needed to translate all codons

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14
Q

non canonical base pairs are allowed at wobble bases (codon #3 to anticodon #1)

A

anticodon U=A or U=G
anticodon G-=C or G=U
anticodon inosinate (I) I=A or I=U or I=C

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15
Q

___________________ read variant sequence elements to select the correct tRNA to be charged with a particular amino acid

A

aminoacyl-tRNA synthetases

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16
Q

the _____________ dictate 3D structure of tRNAs

A

invariant

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17
Q

each amino acid requires its own ___________________

A

aminoacyl-tRNA synthetase

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18
Q

ribosomes are __________ and only ___________ by wieight

A

65% rRNA; 35% protein

19
Q

prokaryotes have one ribosome, ______________

A

the 70S ribosome

20
Q

eukaryotic cells have at least two:

A

80S ribosomes in the cytoplasm and endoplasmic reticulum
mitochondria have a 55S ribosome

21
Q

ribosomes have 3 tRNA binding sites:

A

A site for aminoacyl tRNA ( where charged tRNA enters)
P site for peptidyl tRNA (attached to growing peptide)
E site for empty (where uncharged tRNA goes to exit)

22
Q

polysomes

A

multiple ribosomes bound to a single mRNA

23
Q

______________ act on the _____________.
- _______ blocks premature tRNA binding at the A site
-_______ blocks premature binding of the 50S subunit
-mRNA binds to the 30S subunit by base pairing between the 16S rRNA and the Shine-Dalgarno sequence. (as a result, the AUG start codon is arranged into the P-site)

A

initiation factors; 30S ribosomal unit; IF-1; IF-3

24
Q
A
25
Q

the shine-dalgarno or ribosome binding sequence (RBS) is …

A

8-13 nt purine-rich element in mRNA where ribosomes bind to initiate translation

26
Q

although _____ is always the first amino acid in a prokaryotic protein, the second and each subsequent amino acids can be any one of the 20

A

fMet

27
Q

_______ binds charged initiator fMet-tRNA and escorts it into the P site

A

IF-2-GTP

28
Q

IF-2 hydrolyzes the GTP, resulting in ….

A

dissociation of all IFs

29
Q

the __________ binds forming the complete ___________.
- the complex is now complete
- ____________________:
- A site is vacant
- P site has fMet-tRNA
- E site is vacant

A

50S subunit; 70S ribosome; translation initiaton complex

30
Q

_________________ act on the 70S ribosome

A

elongation factors (EFs)

31
Q

___________ binds an __________ in the cytoplasm and delivers this charged tRNA to the ribosomal A site.
- base pairing occurs between the aminoacyl-tRNA anticodon and the second codon in the mRNA.
- tetracyclines bind to the 30S subunit blocking aminoacyl-tRNA entry into the A site

A

EF-Tu-GTP; amino acyl-tRNA

32
Q

____________ hydrolyzes GTP-> GDP + Pi and exits
- A site has an aminoacyl-tRNA
- P site contains fMet-tRNA
- E site remains vacant

A

EF-Tu-GTP

33
Q

EF-Tu-GDP is recycled to EF-Tu-GTP by _________

A

EF-Ts

34
Q

the ribosome is a ___________.
- the free amino group on the acyl-tRNA in the A site attacks fMet-tRNA in the P site
- fMet is transferred to nascent chain in the A site forming the first peptide bond

A

peptidyl transferase

35
Q

_____________ binds 50S subunit blocking peptidyl transferase activity

A

chloramphenicol

36
Q

the ________________ moves the mRNA through the cleft in the ribosome

A

EF-G GTP translocase

37
Q

___________ binds near the A site
- GTP-> GDP shifts ribosome down one codon on the mRNA
- A site is again vacant
- P site contains dipeptidyl-tRNA
- E site has an uncharged tRNA that quickly dissociates
- _____________ binds to the 50S ribosomal subunit rRNA and blocks the binding site for EF-G

A

EF-G GTP; erythromycin

38
Q

___________ changes shape of rRNA in 30S subunit, causing ribosome to misread mRNA

A

streptomycin

39
Q

at a stop codon, the ribosome …

A

pauses and waits for a new charged tRNA

40
Q

a ___________ recognizes the stop codon and binds to the A site (essentially tricks ribosome into thinking its a charged tRNA)
- ____________ activate peptidyl-transferase hydrolyzing the peptidyl-tRNA bond terminating translation

A

release factor (RF)

41
Q

_____________ and ______ dissociate the complex
______ rebinds to 30S subunit

A

ribosome recycling factor (RRF) and EF-G; IF-3

42
Q

how is eukaryotic translation different from prokaryotic translation?

A

mRNAs are synthesized and RNA processed in the nucleus
- mRNA is transferred to the cytoplasm where it may be intercepted by miRNA-RISC

43
Q

the __________ carries out translation. (eukaryotes)

A

80S ribosome

44
Q

eurkaryotic translation initiation complex
- ____ brings charged Met-tRNA to the _____________ before the mRNA
- ____ complex binds to the mRNA 5’ cap and brings it to the 40S
- the ribosome scans the mRNA 5’->3’ to locate the AUG within a ______________
- ___________ binds to complete the _____________

A

eIF2; 40S subunit; eIF4; Kozak sequence; 60S subunit; 80S ribosome

biochem (37 decks)

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