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Molecular Biology > Translation > Flashcards

Translation Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Triplet codon

A

1 triplet codon or 3 bases codes for 1 amino acid.

Note it is in RNA code so UGAC

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2
Q

Translation involving mRNA structure

A 
In 5' to 3' direction
Ribosomal binding site
Start codon
Coding sequence
Stop codon
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3
Q

Ribosomal binding site

A

Site for ribosome binding

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4
Q

Start codon

A

A codon that specifies the first amino acid in a polypeptide sequence to be translated

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5
Q

Coding sequence

A

A series of codons from start codon to stop codon that determine amino acid sequence of a polypeptide.

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6
Q

Stop codon

A

Specifies the end of translation

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7
Q

List the 5 components for translation

A 
Ribosome
mRNA
Charged tRNA
Initiation and elongation factors
Energy from hydrolysis of GTP
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8
Q

Ribosomes

A

Site of protein synthesis
Consists of rRNA and proteins
Arranged as 2 subunits

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9
Q

List the 2 subunits that make up the ribosomes

A

Small subunit - associates with mRNA

Large subunit - associates with charged tRNA

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10
Q

List the 2 important tRNA binding sites in a large subunit

A

Contains 3 important tRNA binding sites

1) P site
2) A site
3) Exit site

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11
Q

P site function

A

During protein translation, the P-site holds the tRNA which is linked to the growing polypeptide chain

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12
Q

A site function

A

The A site accepts an incoming tRNA bound to an amino acid.

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13
Q

Ribosome large subunit contains peptidyl transferase enzyme

A

it catalyzes the addition of an amino acid residue in order to grow the polypeptide chain in protein synthesis

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14
Q

Ribosomal subunits and rRNA naming after their S value

A

Named using parameters called S value or swedburg value.

S value refers to sedimentation value

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15
Q

Larger ribosomal subunits vs smaller ribosomal subunits

A

Larger ribosomal subunits sediment quicker than smaller ribosomal subunits.

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16
Q

tRNA function

A

Adapts each mRNA triplet codon to tis correct amino acid

17
Q

2 characteristics of tRNA

A
  • Short, composed of 75 to 90 nucleotides

- Single stranded RNA, folds on itself to form secondary structure

18
Q

List 2 structures and their functions of tRNA

A

1) Anti-codon loop
Each tRNA contains 3 unpaired bases (triplet anticodon) at the center of the middle loop which can base pair with the complementary mRNA triplet codon.

2) tRNA 3’ acceptor region
Covalently binds to a specific amino acid and brings it to mRNA at ribosome

19
Q

What is required by tRNA 3’ acceptor region to bind free amino acid

A

Aminoacyl tRNA synthetase and ATP are required to covalently bind free amino acid to the 3’ acceptor region of tRNA.

20
Q

List the 3 Protein factors of Initiation of translation

A

IF1, IF2, IF3

21
Q

IF1 function

A

Stabilize 30S subunit

22
Q

IF2 function

A

Binds tRNA fmet to 30S-mRNA: binds to GTP and stimulate hydrolysis

23
Q

IF3 function

A

Binds 30S subunit to mRNA, dissociate monomers to subunit at termination

24
Q

List the 3 Protein factors of elongation of polypeptides

A

EF-Tu, EF-Ts, EF-G

25
Q

EF-Tu

A

Binds GTP, brings aminoacyl-tRNA to the site of ribosome

26
Q

EF-Ts

A

Generates active EF-Tu

27
Q

EF-G

A

Stimulates translocation, GTP-dependent

28
Q

List the 3 protein factors to cause the termination of transcription and release of polypeptide

A

RF-1, RF-2, RF-3

29
Q

RF-1

A

Catalyzes release of polypeptide chain from tRNA
and dissociation of translocation complex;
specific for UAA & UAG termination codons

30
Q

RF-2

A

Behaves like RF-1; specific for UGA and UAA

31
Q

RF-3

A

F-3 Stimulates RF-1 & RF-2

32
Q

Initiation step

A
  1. Small ribosomal subunit binds to a specific sequence on the mRNA
  2. A specific tRNA with the complementary anticodon
    (UAC), binds to the start codon (AUG) on the mRNA
  3. This tRNA which functions as the initiator tRNA, carries a modified form of methionine called N-formylmethionine (fMet)
  4. Large ribosomal unit then binds to ribosome small unit + mRNA
33
Q

Shine dalgarno sequence

A

Shine-Dalgarno (SD) sequence (prokaryotes)

  • AGGAGG consensus sequence located before mRNA start codon (AUG)
  • Associate with 16S rRNA of small ribosome subunit
34
Q

List the 3 steps In prokaryotes regarding fMet

A
  • > The first amino acid inserted into all proteins is a modified form of methionine called N-formylmethionine (fMet) using tRNAf Met
  • > When translation is completed, the formyl group or the entire fMet residue is removed
  • > Normal methionine (Met) is added when AUG appears internally (using tRNAm Met)
35
Q

fMet in bacteria

A

H
Formyl group I
C = O
I
NH O
II II
CH3 - S - CH2 - CH2 - C - C - O
I
H

36
Q

List the 6 steps in Elongation in prokaryotes

A
  1. First charged tRNA is tRNAf Met which occupies the P site of ribosome and base-pairs with AUG (CODON 1) of mRNA.
  2. Second charged tRNA is attracted to the second mRNA codon (CODON 2) by complementary base-pairing and occupies the A site of the ribosome.
  3. Once both P site and A site are filled with charged tRNAs, peptidyl transferase catalyzes the formation of a peptide bond between the two amino acids.
  4. Concurrently, the covalent (ester) bond between the amino acid and the tRNA occupying the P site is hydrolysed, and the uncharged tRNA is released from the P site.
  5. Dipeptide is formed, which is attached to the tRNA at the A site.
  6. Elongation proceeds as ribosomes moves down 1 codon (5’ to 3’ direction).
37
Q

List the 3 steps Termination in prokaryotes

A
  1. Ribosomes translate mRNA until it reaches a stop codon (UAG, UAA, UGA).
  2. When a stop codon occupies the A site of the ribosome, it will be recognized by the ribosome and the finished polypeptide (at P site) is then cleaved from the terminal tRNA.
  3. Polypeptide is released from the translation complex and the ribosome dissociates into large and small subunits
38
Q

List 9 difference in translation between prokaryotes and eukaryotes

A
  • > Ribosomes are larger and protein components are more complex.
  • > mRNAs are much longer lived – most exist for hours (rather than minutes as in prokaryotes).
  • > mRNA is processed to have a 5’ 7mG cap and 3’ poly-A tail and splicing of introns.
  • > The 7mG cap is important for translation, mRNAs without 5’ cap are translated poorly.
  • > Instead of the Shine-Delgarno sequence, there is a Kozak sequence GCCRCCAUGG (a consensus sequence, where R is a purine - A or G).
  • > The start codon AUG is located within the Kozak sequence.
  • > The Kozak sequence marks the initiation of translation, to facilitate the binding to the small subunit of ribosome to mRNA.
  • > There is no need for fMet at the start codon (AUG).

Molecular Biology (9 decks)

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