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Biochemistry > L18-19: Translation > Flashcards

L18-19: Translation Flashcards

1
Q

What are features of the genetic code?

A

Non-overlapping
Degenerate
Universal

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2
Q

What is the primary structure of tRNA?

A

Small nucleic acids of 70-90nts
Have a 5’ monophosphate
Contain modified bases:
Ribothymidine
Pseudouridine
Dinydroïridine
Inosine

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3
Q

What are features of tRNA secondary structure?

A

D loop: dinydrouridine
T loop: pseudouridine
Variable arm
Anticodon loop
Amino acid acceptor site

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4
Q

How are tRNAs aminoacylated?

A

Through tRNA synthetases:
Amp added to give aminoacyl adenylate
Which reacts with appropriate uncharged tRNA to give aminoacyl tRNAand AMP

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5
Q

What are the differences between the a different classes of aminoacyl tRNA synthetases?

A

Specific enzymes for 10/20 essential amino acids so bind different faces on tRNA

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6
Q

How are tRNA molecules distinguished?

A

Using identity elements

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7
Q

How does proofreading by aminoacyl tRNA synthetases take place?

A

Acylation site rejects amino acids that are larger than the correct one
Editing site hydrolytic cleaves amino acids that are smaller than the correct one

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8
Q

How do codons and anticodons interact?

A

In an anti-parallel fashion (tRNAs are able to recognise more than one codon)

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9
Q

What is the Wobble Hypothesis?

A

The codon and anticodon pair with usual rules (A-T, G-C)
The base at the 5’ end of the anticodon can form a non-standard H bond with the base at the 3’ end of the codon

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10
Q

What can the different bases pair up with according to the Wobble Hypothesis?

A

A-U
C-G
U-A/G
G-C/U
I (Inosine)-A/C/U

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11
Q

What is the composition of prokaryotic ribosomes?

A

50s:
31 different proteins (L), 23s rRNA & 5s rRNA
30s:
21 different proteins (S) & 16s rRNA

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12
Q

What does the s stand for on ribosomes?

A

Svedberg unit - measure sedimentation rate in a centrifuge and thus size and shape

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13
Q

What are the stages of translation and what do they entail?

A

1) Initiation:
Initiation factors 1-3 & GTP
Initiator tRNA
2)Elongation:
Elongation factors & GTP
3) Termination
Stop codon
Release factors 1&2

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14
Q

What is the initiator tRNA?

A

fMet - N-formylmethionine

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15
Q

How is protein synthesis initiated?

A

A special tRNA brings formylmethionine to the ribosome at the AUG start codons

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16
Q

How is initiator tRNA formed?

A

tRNAf combines with methionine to form formylmethionine then transformylase forms Formylmethionyl-tRNAf (fMet-tRNAf)

17
Q

How does initiation take place?

A

30s subunit of the ribosome binds to the ribosome binding site at near the start codon (AUG) then the initiator tRNA (fMet-tRNAf) binds then the 50s subunit binds which forms the 70s initiation complex (sites A,P & E)

18
Q

What are the A,P and E sites composed of?

A

A: Amino acyl site
P: Peptidyl site
E: Exit (empty) site

19
Q

What is the Shine Dalgarno sequence?

A

It properly positions the 30s ribosomal subunit by base pairing with the Shine Dalgarno sequence and 16s rRNA

20
Q

What are the roles of the initiation factors?

A

IF1&3 bind to a free 30s
IF2 binds to GTP
30s attaches to mRNA
Charged initiator tRNA binds and IF3 released
50s binds displacing IF1&2 GTP is hydrolysed

21
Q

What is the process of elongation?

A

-Delivery of aminoacyl tRNA to the A site
-Peptide bond formation
-Translocation

22
Q

What factors are required during the steps of elongation?

A

Delivery requires:
EF-Tu, EF-Ts & GTP
Translocation requires:
EF-G & GTP

23
Q

How are the elongation factors used in the delivery step?

A

EF-Tu allows GTP to get hydrolysed to GDP which is the regenerated back to GTP using EF-Ts

24
Q

How are the elongation factors used in the translocation step?

A

EF-G allows the hydrolysis of GTP to GDP which then produces EF-G on its own

25
Q

How is the peptide bond formed in translation?

A

Amino group attacks carbonyl group of the ester linkage which forms the peptide bond and releases the deacylated tRNA

26
Q

What factors are used in termination?

A

Release factors

27
Q

How does the termination process take place?

A

RF1 recognises UAA and UAG
RF2 recognises UAA and UAG
RF£.GTP helps the 2 release factors carry out termination RRF & EF-G promote dissociation of the ribosome

Biochemistry (10 decks)

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