How ribosomes decode mRNA Flashcards Preview

BS2091 Biochemistry I: from genes to proteins > How ribosomes decode mRNA > Flashcards

Flashcards in How ribosomes decode mRNA Deck (42):
1

Mutation in Arg-minus mutant strains affect enzymes in what pathway?

Arginine biosynthetic pathway

2

When streptomycin is present, do Arg-minus mutants grow in the absence of arginine or not?

They grow in the absence of arginine

3

How does the 'leaky' mutant affect the growth of Arg-minus mutants in the absence of arginine?

Growth is slow

4

Does low streptomycin enhance or prevent growth of the Arg-minus mutants?

It enhances it

5

Does low streptomycin enhance or prevent growth of the Arg-minus mutants?

It enhances it

6

Give examples of other strains of mutant that are derived from the 'leaky' mutant and which the additional mutations involve altered ribosomes

- SM-resistant (SM-R) strains = non-leaky
- Other mutations (ram) increased leakiness

7

Who discovered that SM caused 'misreading' of mRNA in vitro?

Julian Davies, Walter Gilbert and Luigi Gorini

8

What can be deduced from the work of Julian Davies, Walter Gilbert and Luigi Gorini?

- mRNA can be misread by ribosomes
- Misreading is enhanced by a drug (streptomycin) that binds to ribosomes
- Mutations resulting in altered ribosomes can either reduce or enhance misreading

9

What can be deduced from the work of Julian Davies, Walter Gilbert and Luigi Gorini?

- mRNA can be misread by ribosomes
- Misreading is enhanced by a drug (streptomycin) that binds to ribosomes
- Mutations resulting in altered ribosomes can either reduce or enhance misreading

10

Ribosomes don't just catalyse protein synthesis, they monitor and control what?

Fidelity of mRNA decoding

11

Ribosomes don't just catalyse protein synthesis, they monitor and control what?

Fidelity of mRNA decoding

12

What happens to the aa-tRNA if they are cognate?

Retained in A site

13

What happens to the aa-tRNA if they are non-cognate?

Ejected from ribosome

14

GTP hydrolysis in either case (when aa-tRNA is retained or ejected) is proofreading at what?

At a cost

15

The ribosome has evolved to deliver what?

Optimal growth rate

16

The ribosome has a need versus what accuracy?

Need versus cost accuracy

17

Ribosomes must generate what to enable codon-anticodon pairing?

A water-free zone

18

Ribosomes do not distinguish cognate versus non-cognate pairs merely by counting what?

H-bonds

19

Do ribosomes know what they are looking for or not?

Yes

20

In order for ribosomes to monitor codon-anticodon pairs, they require a what?

'Decoding site'

21

In order for ribosomes to monitor codon-anticodon pairs, they require a what?

'Decoding site'

22

Where is the decoding site?

On the 30S/40S ribosomal subunit where codon-anticodon recognition occurs

23

What is 'accommodation'?

When the aa-tRNA enters the A site properly

24

What happens to the tRNA component as the ternary complex binds to the ribosome?

It gets distorted

25

What happens to the tRNA component as the ternary complex binds to the ribosome?

It gets distorted

26

In the decoding site of the ribosome, incoming tRNA within ternary complex can be:

- Cognate: a perfect match to the mRNA codon
- Near-cognate: a near-perfect match to the mRNA codon
- Non-cognate: a mismatch to the mRNA codon

27

What did Venki Ramakrishnan research?

The selection of aa-tRNA in ribosomal decoding site

28

What did Venki Ramakrishnan research?

The selection of aa-tRNA in ribosomal decoding site

29

What does the ribosome monitor during aa-tRNA selection?

Base pair geometry

30

What does the ribosome measure base-pair geometry on?

The minor groove side of prospective codon-anticodon pairs and in this way determines whether such base-pairs are complementary

31

Inspection of the major groove of the DNA helix reveals what?

The sequence of dsDNA or dsRNA

32

Inspection of the minor groove of the DNA helix reveals what?

Whether a base-pair obeys Watson-Crick complementary pairing

33

Inspection of the minor groove of the DNA helix reveals what?

Whether a base-pair obeys Watson-Crick complementary pairing

34

The ribosomal proofreading of aa-tRNA selection in decoding site involves what?

2 independent selection steps separated by an irreversible event (GTP hydrolysis_Tu-GDP departure)

35

What can happen to the ternary complex [aa-tRNA-EFTu-GTP] during the first selection step?

Can be lost/ejected

36

What can happen to the aminoacyl-tRNA during the second step?

Can be lost

37

What is the overall error frequency in aa-tRNA selection and is this an acceptable error frequency?

~1 in 10^4
This is an acceptable error frequency

38

What is another name for the 'pre-A site'?

The 'A/T site'

39

What is the 'pre-A site'?

The preliminary site into which the ternary complex binds

40

What happens in selection 1?

Ternary complex containing non-cognate tRNA is rejected

41

What happens between selection 1 and selection 2?

GTP hydrolysis and then accommodation of aa-tRNA

42

What happens in selection 2?

aa-tRNA containing near-cognate tRNA is rejected