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BGM1002-Biochemistry > BGM1002/L18 Translation I > Flashcards

BGM1002/L18 Translation I Flashcards

1
Q

Give the 4 main features of the genetic code?

A

Triplet
Non-overlapping
Degenerate/redundant
Universal

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2
Q

How many combinations does a triplet code allow?

A

4^3
64

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3
Q

How many stop codons are there?

A

3

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4
Q

How many codons specify amino acids?

A

61

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5
Q

How many start codons are there?

A

1 (MET)

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6
Q

In what organism is the CUG codon reassigned from Leu to Ser?

A

Candida albicans (yeast)

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7
Q

How many species of tRNA exist in E. coli?

A

46

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8
Q

Describe the primary structure of tRNA. (3)

A

Small - 70-90 nucleotides
Have 5’ monophosphate (rather than 5’ triphosphate)
Contain modified bases

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9
Q

Name the 4 modified bases that exist in tRNA.

A

Ribothymidine
Pseudouridine
Dihydrouridine
Inosine

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10
Q

Describe the secondary structure of tRNA. (5)

A

D-loop (contains dihydrouridine)
T-loop (contains pseudouridine)
Variable arm
Anti-codon loop
Amino acid acceptor site

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11
Q

What is the 3’ terminal nucleotide sequence in tRNA?

A

-CCA

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12
Q

What are tRNAs joined to amino acids called?

A

Aminoacyl tRNA
Charged tRNA

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13
Q

What type of enzymes catalyse aminoacylation of tRNAs?

A

tRNA synthetases

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14
Q

Describe aminoacylation of tRNA. (3)

A

AMP added to carboxyl group of amino acid
High energy intermediate formed - aminoacyl adenylate
Aminoacyl adenylate reacts with appropriate uncharged tRNA

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15
Q

Which hydroxyl are amino acids joined to on tRNA?

A

2’ or 3’
Once joined, two species can interconvert

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16
Q

Name the 2 classes of tRNA synthetases.

A

Class I
Class II

17
Q

Name the differences between each class of tRNA synthetases. (2)

A

Each contains enzymes specific for 10/20 amino acids
Bind different faces of tRNA molecule

18
Q

How do tRNA synthetases differentiate between similar tRNA molecules?

A

Identity elements on tRNA molecules

19
Q

What are identity elements?

A

Single nonstandard base pairs

20
Q

What mutation prevents aminoacylation of alanine in tRNA^ala?

A

G3 or U70

21
Q

How can aminoacyl tRNA synthetases differentiate very similar amino acids?

A

Proofreading function

22
Q

What allows some aminoacyl tRNA synthetases to differentiate between similar amino acids?

A

Editing site
Aminoacylation/activation site

23
Q

What is the function of the acylation site of aminoacyl tRNA synthetases?

A

Rejects amino acids larger than the correct one

24
Q

What is the function of the editing site of aminoacyl tRNA synthetases?

A

Hydrolytic cleaves amino acids smaller than the correct one

25
Q

What is the nomenclature of cognate tRNAs? Using Leu as an example.

A

tRNA^Leu

26
Q

What is the nomenclature of cognate tRNA synthetases? Using Leu as an example.

A

Leucyl-tRNA synthetase

27
Q

What is the nomenclature of aminoacyl-tRNAs? Using Leu as an example.

A

Leucyl-tRNA^Leu OR
Leu-tRNA^Leu

28
Q

Why must some tRNAs recognise more than one codon?

A

Number of distinct tRNAs is less than number of codons

29
Q

Describe the Wobble Hypothesis.

A

First two bases of the codon base pair with the anticodon according to normal rules
Base at 5’ end of anticodon can form non-standard H-bonds with 3’ end of codon

30
Q

Describe the Wobble prediction of 5’ anticodon A and 3’ codon U.

A

A converted to I by anticodon deaminase

31
Q

Describe the Wobble predictions of 5’ anticodon C and 3’ codon G.

A

No Wobble

32
Q

Describe the Wobble predictions of 5’ anticodon U and 3’ codon A or G.

A

U not found as 5’-anticodon base

33
Q

Describe the Wobble predictions of 5’ anticodon G and 3’ codon C or U.

A

As predicted

34
Q

Describe the Wobble predictions of 5’ anticodon I and 3’ codon A or C or U.

A

As predicted

35
Q

Give the 4 Wobble base pairs.

A

I=C
I=U
I=A
G=U

BGM1002-Biochemistry (29 decks)

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