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Biochem > Translation > Flashcards

Translation Flashcards

1
Q

Nirenberg and Matthaei

A

breaking of genetic code resulted from studies of protein synthesis using cell-free extracts of E. coli and synthetic mRNAs

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2
Q

complete mRNA genetic code noteworthy facts

A
  • codons refer to base triplets in mRNAs
  • 61 of 64 trinucleotides are referred to as sense codons. others are nonsense
  • codons are 5’ to 3’
  • amino acids can be encoded by more than one codon
  • aug = start
  • uaa, uag, uga = stop
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3
Q

given a protein sequence, can you tell what the DNA/RNA sequence was?

A

no

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4
Q

degenerate

A

multiple codons can specify a single amino acid

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5
Q

specific/unambiguous

A

each codon specifies only one amino acid

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6
Q

non-overlapping

A

one a start codon is recognized, there is only one correct “reading frame” of triplets

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7
Q

no punctuation

A

once initiated, bases are read continuously (without pausing) until a stop codon is reached

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8
Q

universal

A

translation process and coding in all species is always the same

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9
Q

tRNA

A
  • each tRNA has an anticodon loop that has 3 bases that can base pair with the mRNA
  • we don’t have one tRNA per codon
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10
Q

wobble hypothesis

A
  • proposed by Crick
  • base-pairing at 3rd position is not as as constrained as other 2 bases
  • permits flexibility in codon; anticodon recognition, allowing mRNA translation with < 64 tRNAs
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11
Q

wobble rules

A
  1. the first 2 base pairing in a codon-anticodon interaction confer most of the specificity required for translation
  2. the interactions between the third codon and anticodon nucleotides are less stringent
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12
Q

aminoacyl-tRNAs

A

-formation is two step reaction

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13
Q

class 1 aminoacyl-tRNAs

A

function as monomers

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14
Q

class 2 aminoacyl-tRNAs

A

function as polymers or dimers

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15
Q

requirements for protein synthesis

A
  • mRNA transcript
  • assorted supply of aminoacyl-tRNAs
  • large and small ribosomal subunits
  • assorted initiation and elongation factors
  • GTP-energy
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16
Q

shine-dalgarno sequences

A
  • in prokaryotes

- help align mRNA to ribosome so translation begins at appropriate position

17
Q

components of bacterial ribosomes

A

70s made up of 50s and 30s subunits

18
Q

components of eukaryotic ribosomes

A

80s ribosome is similar in structure to bacterial ribosome but composed of 60s and 40s subunit

19
Q

In eukaryotes, which RNA polymerase would be responsible for transcribing the rRNA in the large subunit of the ribosome?

A

RNA Pol I

20
Q

In eukaryotes, which polymerase would be responsible for transcribing rRNA in the small subunit?

A

RNA Pol III

21
Q

In prokaryotes, which RNA polymerase is responsible in transcribing the large subunit rRNA?

A

They only have one RNA polymerase

22
Q

initiation of translation

A
  • binding of mRNA, ribosomal subunits, and first aminoacyl-tRNA
  • IF1 and IF3 bind to 30s subunit
  • 30s subunit binds to Shine-Dalgarno sequence upstream from AUG
  • 30s subunit slides 5’ to 3’ to position AUG start codon in P site
  • Ensures first AUG is located
  • IF2 w GTP binds to 30s A site
  • GTP hydrolyzed
23
Q

elongation of translation

A
  • sequential formation of all peptide bonds
  • before it begins, peptide chain is attached to P site and E and A sites are empty
  • recognized aminoacyl-tRNA then binds in A site with help of EF-Tu elongation factor
  • peptide bond is formed by peptidyltransferase region
  • ribosome translocates to move P site tRNA to E site, and newly added peptide-tRNA from A site to P site
24
Q

termination of translation

A
  • stop codon recognition, release of polypeptide and dissociation of ribosome subunits
  • when ribosome encounters stop codon, no tRNA complementary to codon
  • release factor binds the A site
  • peptidyl-tRNA is attacked by a water molecule, releasing peptide
  • release factor RF3 releases process through GTP binding and hydrolysis
  • ribosome then dissociates from mRNA
25
Q

poly-ribosomes

A
  • multiple ribosomes attached to a single mRNA

- up to 50 can be attached to one mRNA

26
Q

difference in ribosome subunits prok and euk

A

prok: 30S + 50S = 70S
euk: 40S + 60S = 80S

27
Q

difference in mRNA processing prok and euk

A

prok: rRNas and tRNAs
euk: rRNAs, tRNAs, and mRNAs

28
Q

difference in transcript recognition prok and euk

A

prok: Poly-G/A shine-dalgarno sequence
euk: 5’ cap and poly A tail

29
Q

difference in rate of transcription prok and euk

A
  • prok: 20 amino acids per sec, coupled to transcription

- euk: 1 amino acid per sec, not coupled to transcription

Biochem (12 decks)

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