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BCMB 2001 - Biochemistry and Molecular Biology > Translation > Flashcards

Translation Flashcards

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1
Q

Start Codon

A

AUG

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2
Q

Stop Codons

A

UAA, UAG, UGA

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3
Q

Degenerate nature of the code

A

More than one codon codes for the same amino acid.

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4
Q

Ribosome Subunits

A

Two subunits:
1. 50s
2. 30s
NOTE: s = sedimentation rate

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5
Q

Shine Dalgarno Sequence

A

Sequence of RNA before the start codon

Ribosome binding site

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6
Q

Amino acids

A

19 are Cα amino acids (Cα connected to amino group + carboxylic acid group -> look at notes for diagram).
1 is an imino acid -> in a chain

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7
Q

Amino acid side chains

A

Determine the chemistry and structure of the protein -> therefore, determine function.

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8
Q

tRNA

A

Single strand of RNA
5’ = acceptor stem -> determines which amino acid is attached
3’ = CCA terminus -> where amino acid attaches
Anti codon = binds to a specific codon
mRNA = anti parallel orientation

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9
Q

Wobble Pairing

A

1st base of anti-codon does not have to pair perfectly e.g G can pair with both C and U
Results in there being approx 30-40 types of tRNA

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10
Q

Aminoacyl - tRNA Synthetases (AARS)

A

Attach amino acids to tRNA - uses anti-codon to select correct tRNA + acceptor stem.
20 different AARS (one for each amino acid)
Two types:
1. Class I = attach amino acid to 2’ OH
2. Class II = attach amino acid to 3’ OH

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11
Q

Prokaryotic mRNA

A

Polycisronic: codes for more than one polypeptide
No 5’ cap or 3’ poly A tail
Ribosomal binding site possesses Shine-Dalgarno sequence -> recruit translation machinery.

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12
Q

Eukaryotic mRNA

A

Monocistronic: codes for one polypeptide
5’ cap recruits ribosome
3’ cap increases efficiency of translation (located near stop codon)
Kozak sequence: increases the efficency of translation (help identify the start codon).

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13
Q

Eukaryotic Translation Initiation

A
  1. Preparation of mRNA
  2. Preparation of the small ribosomal subunit
  3. Assembly of the 80s initiation complex
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14
Q

Eukaryotic Translation Initiation - preparation of mRNA

A

Eukaryotic initiation factor 4E (eIF4E) binds to 5’ cap of mRNA
Recruits additional initiation factors
Unwinds mRNA

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15
Q

Eukaryotic Translation Initiation - Preparation of the small ribosomal subunit

A

Initiation factors bind to small ribosomal subunit -> prevents binding of large subunit + tRNA to small subunit
Ternary complex: tRNA imet + eIF2-GTP) bind to P site of the small subunit

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16
Q

Eukaryotic Translation Initiation - Assembly of the 80s initiation complex

A

1st the 48s pre-initiation complex binds to the small subunit -> scan mRNA for the start codon -> releases initiation factors when the start codon is recognised
Because the initiation factors are lost the large subunit is able to bind to the small subunit to form the 80s initiation complex
Poly A binding proteins bind to the poly-A tail -> aid recruitment of initiation factors + stabilize mRNA

17
Q

3 tRNA binding sites in ribosome

A 
E = exit site
P = peptidyl site
A = acceptor site
18
Q

Eukaryotic Translation Elongation

A

Elongation factor EF-TU delivers charged tRNA to the A site.
tRNA with amino acid binds to the P site -> polypeptide chain transfered to the tRNA at the A site
tRNA at P site exits at E site + tRNA with polypeptide chain in A site translacoates to the P site (caused by hydrolysis of GTP from EF-G-GTP).
Ribosome then moves along the mRNA by 3 bases unit it reaches the stop codon.

19
Q

Eukaryotic Translation Termination

A

Eukaryotic release factor 1 (eRF1) recognises stop codons -> causes the ribosome to release the polypeptide chain.

20
Q

Translation Regulation

A
  1. Quality Control

2. Degradation of defective mRNA (non-sense, non-stop, no-go)

21
Q

Translation Regulation - Quality Control

A

Hydrogen bonds form between tRNA +mRNA and ribosome + mRNA -> if pairing is incorrect weak bonds
Incorrect pairing impairs the functioning of the elongation factor -> prevents GTP hydrolysis on the tRNA in the A position (rotates) -> no energy to transfer the peptide chain from P to A.

22
Q

Translation Regulation - Degradation of defective mRNA: non-sense

A

Displacement of exon junction complexes -> causes a premature stop codon to be displayed
The incorrect stop codon will be recognized by the release factor + will cause the peptide chain to be released
Enzymes remove 5’cap and poly-A tail
Ribosome removed + 5’->3’ exonuclease degrades uncapped RNA.

23
Q

Translation Regulation - Degradation of defective mRNA: non-stop

A

No stop codon present
Ribosome translates to the end of the mRNA
Proteins bind to A site of ribosome -> remove polypeptide chain + dissociates mRNA from ribosome
Poly-Lysine peptide + mRNA degraded

24
Q

Translation Regulation - Degradation of defective mRNA: no-go

A

Ribosome stops before stop codon
Proteins bind to ribosome + cause it to release the polypepide chain
Polypeptide chain incomplete so degraded

25
Q

Translation Regulation - Cells

A

Translation encouraged: eIF4E-BP phosphorilated by a kinase -> not able to bind to initiation factor.
Translation stopped: eIF4E-BP not phosphorilated -> binds to initiation factor + blocks ribosome binding.

26
Q

Translation + Regulation of Iron Homeostasis

A

Ferritin: stored Fe in cells
Translation of ferritin + transferrin receptor regulated by Iron-regulatory proteins (IRP) which bind to iron regulatory elements (IRE) in mRNA.

27
Q

Translation + Regulation of Iron Homeostasis - Low Iron Level

A

Ferritin mRNA + transferrin receptor mRNA is recognised by IRPs.
Not able to be translated when IRP is bound -> reduce Fe storage + thus increase the amount available in the blood.
IRP bound to tranferrin receptor: stabilised, increases translation + Fe uptake.

28
Q

Translation + Regulation of Iron Homeostasis - High Iron Level

A

IRPs are bound to Fe and are not able to bind to mRNA
Ferritin mRNA: translation active -> increase Fe storage
Transferrin receptor mRNA: mRNA unstable with no IRPs bound ->reduced translation -> reduced Fe uptake.

29
Q

Unconventional Initiation of Translation

A

Internal ribosome entry site (IRES) in circular genome rather than 5’ cap
Initiation factors bind to IRES
Can be found in between two open reading frames -> direct translation of 2nd peptide.

BCMB 2001 - Biochemistry and Molecular Biology (4 decks)

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