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Molecular Bio > Mod 7 - From RNA to Protein > Flashcards

Mod 7 - From RNA to Protein Flashcards

1
Q

What is translation?

A

protein synthesis - conversion from mRNA to a protein

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2
Q

what is a codon?

A

3 nucleotide (triplet) code used to specify amino acids

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3
Q

what is the function of aminoacyl tRNA snythetase?

A
  • each tRNA is recognised by 1 of 20 aminoacyl tRNA synthetases
  • some tRNAs recognise more than 1 codon
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4
Q

how does one tRNA recognise more than one codon?

A

wobble
- allows unconventional base pairing between third base in codon and first base in anticodon
- e.g. G-U base pairing
- e.g. inosine (guanine) can pair with A, C, and U

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5
Q

what are the 3 stages of protein synthesis?

A
  • initiaiton
  • elongation
  • termination
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6
Q

what are some of the prerequisites for protein synthesis?

A
  • machinery (ribosomes or cofactors)
  • Energy (e.g. ATP or GTP)
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7
Q

what kind of ribosomes do eukaryotes and prokaryotes have?

A
  • euk = 80s ribosomes
    -prok = 70s ribosomes
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8
Q

What are the 2 ribosomal subunits in prokaryotes?

A
  • 50s subunit
  • 30s subunit
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9
Q

What are the 2 ribosomal subunits in eukaryotes?

A
  • 60s
  • 40s
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10
Q

why does 2 + 2 not necessarily equal 4? (ribosomal)

A
  • measure of S is svedberg - a measure of shape as well as size
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11
Q

How are amino acids activated? (start of protein synthesis)

A
  • amino acids couples with ATP molecule (transesterification)
  • forms aminoacylAMP
  • aminoacyl segment couples with tRNA

2 step process
- AA + ATP -> AA-AMP + PP
- AA-AMP + tRNA -> AA-tRNA + AMP

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12
Q

what is a shine-dalgarno sequence?

A
  • a sequence of bases with methionine (start codon) embedded
  • known as Kozak sequence in eukaryotes
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13
Q

what are the molecules involved with initiation of translation?

A
  • specific initiator methionine tRNA
  • initiation factor 2 (IF2) - covalently bonded to GTP (known as a G protein)
  • 30s ribosomal subunit bonded to IF1 and IF3
  • mRNA containing an AUG (within a shine-dalgarno sequence)
  • large subunit of ribosome (including P site and A site)
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14
Q

what are the steps in initiation of translation?

A
  • IF2 G protein couples with 30s subunit
  • initiator tRNA (with formylmethionyl) couples with mRNA
  • large subunit assembles with the newly formed complex to complete initiation complex

side effects
- ATP -> ADP
- GTP -> GDP (still bound to IF2 but becomes hydrolysed)

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15
Q

what is the function of IF1 ?

A

blocks A site on large subunit to tRNA-met, inhibits premature 30S-50S interaction

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16
Q

What is the function of IF2 ?

A

tags tRNA and regulates entry into ribosome

17
Q

What is the function of IF3 ?

A
  • inhibits premature 30S-50S interaction
  • stabilises free 30S
  • accuracy check for tRNA-met binding
18
Q

what is the elongation factor required for the elongation step called?

A

aminoacyl tRNA-EFTu-GTP
(is a G protein because it is bound to GTP)

19
Q

what is special about tRNA-Met i?

A
  • the only tRNA which can bind to the P site
  • P site = peptidyl-tRNA site - peptide bond formation
20
Q

what is the function of EFTu-GTP?

A
  • lines up the next amino acid on the A site next to the first methionine
  • causes ejection of EFTu-GDP (hydrolyses)

A site = aminoacyl-tRNA site (acceptor site) - where incoming aminoacyl-tRNA binds

21
Q

what happens after the second amino acid is placed on the mRNA?

A
  • ribosome translocates from having its P site on AA 1 to AA2, and having its A site on AA2 to AA3 (translocates whole molecule one amino acid downstream)
  • this means peptidyl tRNA is now in P site, A site is free
22
Q

what is the function of the different elongation factors?

A
  • EF-Tu = mediates aminoacyl-tRNA entry to ribosome
  • EF-G = mediates translocation of ribosome
23
Q

How does termination occur?

A
  • when a termination codon (UAA, UGA, UAG) appears, a release factor (RF-GTP) binds to the A site
  • when RF is bound, hydrolysis of polypeptide chain from tRNA occurs
  • ribosome then dissociates from polypeptide
24
Q

what is the role of GTP?

A
  • GTP = guanosine triphosphate
  • provides energy via hydrolysis - GTP -> GDP + Pi
25
Q

what stages of protein synthesis is GTP involved in?

A
  • ALL stages
  • initiation = addition of large subunit
  • elongation = addition of aminoacyl-tRNA by EF-Tu, peptide synthesis, translocation
  • termination = release of peptide chain + dissociation of ribosome

Molecular Bio (8 decks)

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