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Flashcards in Translation Deck (31)
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1
Q

How does mRNA reach ribosomes?

A

Moves through nuclear pores to cytoplasm

2
Q

Where are ribosomes found?

A

Free in cytoplasm

On cytoplasmic surface of RER

3
Q

What happens to proteins made on RER ribosomes?

A

Secreted /targeted to organelles or inserted into plasma membrane

4
Q

What happens to protein made in free ribosomes in cytoplasm?

A

Remain in cytoplasm

5
Q

What 2 components does ribosome consist of?

A

rRNA and protein

6
Q

What forms the ribozyme (key reactive site in ribosome)?

A

rRNA

7
Q

What does each ribosome consist of?

A

80S complex with ribonucleoprotein subunits

large 60s subunit contains 3 RNAs

small 40s subunmit

8
Q

Where are ribosomal subunits made?

A

Nucleolus

9
Q

What do tRNAs do?

A

Carry specific amino acids to ribosomes (sequence determined by mRNA template)

10
Q

What does aminoacyl-tRNA synthetase do?

A

aminoacyl-tRNA syntheses recognises tRNA and catalyses transfer of correct amino acid to the 3’ end of the correct tRNA (formation of aminoacyhl-tRNA).

11
Q

What end of the tRNA does the AA join?

A

3’ end

12
Q

Describe the accuracy of aminoacyl tRNA synthetase, why?

A

Enzyme is highly specific

tRNA synthetase only engages particular tRNAs and proof reading ensures accuracy in process

13
Q

What is an anticodon?

A

Region of tRNA, Sequence of 3 bases that regonises codon on mRNA

14
Q

How can some tRNAs recognise more than one codon?

A

Wobble hypothesis: often a triplet of 2 specific bases followed by any base codes for same amino acid.

3rd base more tolerant with the number of H bonds that form - wobble position

15
Q

What initiates translation?

A

Cap at 5’ end recruits 40s subunit

40s scans mRNA for start codon (AUG)

Initiation factor proteins (IFP), GTP and met-tRNAi are bound to 40s subunit

16
Q

Describe structure of ribosome 60s subunit, how does peptide bond form?

A

3 tRNA binding sites

E (exit) site

P (met-tRNAi) site p

A(tRNA) site

Peptide bond forms between amino acids by peptidyl transferse when correct tRNA in A site

17
Q

Describe what happens initially as movement of ribosome in translation?

A

Moves along RNA towards 3’ end by one codon (driven by GTP and elongation factors)

met-tRNA (methionine tRNA first one) released through E site

tRNA with growing chain in P site

A site free to bind next tRNA

18
Q

What is met-tRNAi?

A

Initiator tRNA conjugated to methionine

19
Q

What is the start codon?

A

AUG

20
Q

What are the stop codons?

A

UAA, UGA, UAG

21
Q

How can you remember the stop codons?

A

U are annoying, U are gross, U go away

22
Q

What bond joins an AA to a tRNA?

A

Ester

23
Q

What is required to form AA-tRNA bond?

A

ATP

24
Q

What does the 40s do vs the 60s?

A

40s - scans mRNA

60s - joins AA

25
Q

What are the three tRNA binding sites of the 60s unit?

A

E (exit site)

P (met-tRNAi) site p

A(tRNA) site

26
Q

How does the polyA tail recruit mRNA to ribosome?

A

Associates with proteins (poly-A binding protein) recruiting the mRNA to the ribosome.

27
Q

How is the 5’ cap involved in translation ?

A

Key in initiation

Small ribosomal subunit is recruited to the cap and then scans the mRNA for AUG start codon.

28
Q

How is the code degenerate when base pairing is specific?

A

4^3 possible codons can be formed by AUGC, this would require 61 t-RNA molecules as there is 3 possible stop codons.

In reality there are less than 45 t-RNAs meaning some tRNAs can recognise more than one codon (degenerate code).

tRNAs usually differ in the third base, as the rules at the third position are less strict and it can still base pair with a wobble position

29
Q

What enzyme catalyses peptide bond formation?

A

Peptidyl transferase

30
Q

In the assembled ribosome, there are two binding sites, designated A and P. Progress of the mRNA through the ribosome involves…

A

transfer of the growing polypeptide from peptidyl-tRNA in the P site to the aminoacyl-tRNA in the A site

31
Q

For translation of mRNA into a protein product, tRNA molecules react with…

A

specific aminoacyl-AMPs