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biochemistry > chapter 40 > Flashcards

chapter 40 Flashcards

1
Q

the 50s subunit of the ribosome is composed of

A

34 proteins and a 23S RNA and a 5S RNA

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2
Q

the 30S subunit contains

A

21 proteins and a molecule of 16S RNA

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3
Q

what is the actual catalyst for protein synthesis

A

ribosomal RNA

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4
Q

what are the 3 tRNA binding sites

A

1.The A (aminoacyl) site binds the incoming tRNA.
2.The P (peptidyl) site binds the tRNA with the growing peptide chain.
3.The E (exit) site binds the uncharged tRNA before it leaves the ribosome.

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5
Q

what happens at the A site

A

aminoacyl site binds the incoming tRNA

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6
Q

what happens at the P site

A

peptidyl site binds the tRNA with the growing peptide chain

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7
Q

what happens at the E site

A

exit site binds the uncharged tRNA before it leaves the ribosome

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8
Q

what is the polypeptide channel

A

a tunnel that connects the P site to the back of the ribosome through which the peptide exits the ribosome during synthesis

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9
Q

what is a shine-dalgarno sequence

A

untranslated region that contains information which directs protein synthesis machinery to the start site

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10
Q

the shine-dalgarno sequence is what rich

A

purine rich (A and G)

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11
Q

what is the initiator amino acid in most proteins in bacteria

A

N-formylmethionine

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12
Q

what do initiation factors do

A

assist in the assembly of protein-synthesizing machinery

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13
Q

what do IF1 and IF3 do

A

bind the 30s subunit to prevent premature binding to the 50S subunit

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14
Q

what does IF2 do

A

in cooperation with GTP, delivers fMet-tRNA to the mRNA which is already correctly positioned on the 30S subunit by the SD sequence to form the 30S initiation complex

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15
Q

how does the 70S initiation complex form

A

50S subunit binds, leading to the hydrolysis of GTP by IF2 and departure of the initiation factors

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16
Q

what is accommodation

A

If the anticodon pairs with the codon, GTP is hydrolyzed, and EF-Tu-GDP
departs, with the A site now occupied by the appropriate aminoacyl tRNA

17
Q

what does EF-Tu do

A

bring the appropriate aminoacyl-tRNA to the A site (with the help of GTP)

18
Q

what does EF-Ts do

A

induces release of GDP from EF-Tu which is then replaced by GTP

RECYCLES EF-Tu!!!!!!

19
Q

what is the peptidyl transferase center and what happens there

A

peptide bond formation is catalyzed on the 23S (part of the 50S subunit)

20
Q

is peptide bond formation exergonic

A

YES, no energy is needed for input

21
Q

elongation factor G is called what

A

translocase

22
Q

what does translocase do

A

uses the energy of GTP hydrolysis to translocate the mRNA by one codon

23
Q

what is translocation for dummies

A

when the guy (translocase) pushes the tRNAs over by one site

the empty tRNA goes to the exit site to prepare to leave, the growing polypeptide chain is bumped over into the P site, and the A site is empty and ready for a new tRNA molecule

24
Q

what are the 3 stop codons

A

UAA, UGA, UAG

25
Q

what recognizes stop codons

A

release factors

26
Q

what does release factor 1 do

A

recognizes UAA/UAG

27
Q

what does release factor 2 do

A

recognizes UAA/UGA

28
Q

what does release factor 3 do

A

FR1/FR2 release

29
Q

what do release factors do

A

RFs recognize stop codons and facilitate the attack of a water
molecule on the ester linkage between the polypeptide chain and
tRNA in the P site, releasing the complete protein.

30
Q

what do EF-G and ribosome release factor (RRF) do

A

catalyze the
dissociation for the ribosome, mRNA, and attached tRNA in a
reaction facilitated by GTP hydrolysis.

31
Q

how is eukaryotic translation more complex than prokaryotic

A
  1. ribosomes are larger
  2. starts with methionine
  3. initiator codon is always the FIRST AUG from the 5’ end of the mRNA
  4. mRNA is circular because of interactions between proteins that bind the 5’ cap and polyA tail
  5. eukaryotes have only 1 release factor
  6. RNA synthesis occurs in the nucleus in eukaryotes
32
Q
A

biochemistry (16 decks)

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