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Building the Organism > Gene Expression - Translation > Flashcards

Gene Expression - Translation Flashcards

1
Q

How many bases in polynucleotides?

A

4

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2
Q

What specifies mRNA nucleotide sequence?

A

DNA

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3
Q

What does the genetic code consist of?

A

non-overlapping triplets which are read from a fixed starting point

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4
Q

Triplet codons:

A

64 codons specify 20 amino acids - 61 ‘sense’ and 3 ‘stop’ codons or nonsense codons

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5
Q

Is genetic code identical in all organisms?

A

yes

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6
Q

Is the genetic code universal?

A

yes

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7
Q

What is the ‘open reading frame’?

A

the protein coding sequences in a gene

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8
Q

For most amino acids…

A
  • there is more than one codon
  • the genetic code is ‘degenerate’
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9
Q

The genetic code is not ambiguous meaning?

A

each codon specifies only on amino acid

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10
Q

Types of RNA involved with translation:

A
  1. mRNA
  2. tRNA
  3. rRNA
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11
Q

Why is an adaptor or interpreter required?

A

as we have no direct pairing between the codons and amino acids

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12
Q

How do tRNAs act as adapter molecules:

A
  • bridges the codon to a specific amino acid
  • each tRNA becomes covalently linked to one specific amino acid
  • each tRNA has a triplet anticodon that recognises one or more codons in the mRNA by base pairing
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13
Q

In response to a specific codon, tRNAs…

A

bring the correct amino acid to the ribosome

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14
Q

What type of structure do tRNAs have?

A

cloverleaf structure

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15
Q

3 functions of tRNA:

A
  1. it binds to an amino acid, and is then “changed”; requires specific features in tRNA
  2. it associates with mRNA molecules through the anticodon loop
  3. it interacts with ribosomes
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16
Q

tRNA charging:

A

specific enzymes couple each amino acid to its appropriate tRNA molecule

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17
Q

What is tRNA catalysed by?

A

aminoacyl-tRNA synthetase

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18
Q

The accuracy of tRNA charging is controlled by what?

A

aminoacyl -tRNA synthetase

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19
Q

Amino acid selection and tRNA selection are subject to what?

A

proofreading

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20
Q

What does proofreading do?

A

either disfavours the forward reaction or reverses the catalytic reaction if the wrong component has been selected

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21
Q

What does proofreading avoid?

A

the need for absolute accuracy(which is slow)

22
Q

tRNA molecules match what to what in mRNA?

A

amino acids to codons

23
Q

Where does codon-anticodon recognition occur?

A

on the ribosome by the base pairing between the codon and anticodon

24
Q

What does ‘wobble’ and modified bases allow?

A

one tRNA to decode more than one codon

25
Q

What is ‘wobble’?

A

flexibility in pairing

26
Q

Wobble hypothesis:

A

Watson-crick base pair rules between anticodon position 1 and codon position 3 are released due to flexibility and modifications of the anticodon loop

27
Q

Can single tRNAs recognise multiple codons?

A

yes

28
Q

Ribosomes:

A

holds mRNA and charged tRNAs in the correct positions to allow assembly of the polypeptide chain

29
Q

What type of proteins can ribosomes make?

A

any meaning they’re not specific

30
Q

In eukaryotes, how many molecules of rRNA and proteins in a large subunit?

A

3 rRNA and 49 proteins

31
Q

In eukaryotes, how many molecules of rRNA and proteins in a small subunit?

A

1 rRNA and 33 proteins

32
Q

rRNA structure:

A

rRNA is highly structured and the major structural and functional component

33
Q

What is peptide bond formation catalysed by?

A

23s rRNA

34
Q

How many sites for tRNA binding on the largest ribosomal subunit?

A

3

35
Q

Codon-anticodon interactions between tRNA and mRNA occur at what sites?

A

P and A sites

36
Q

A site:

A

binds with the anticodon of charged tRNA

37
Q

P site:

A

where tRNA adds its amino acid to the growing peptide chain

38
Q

E site:

A

where tRNA sites before being released from the ribosome

39
Q

3 phases to polypeptide synthesis:

A
  1. initiation
  2. elongation
  3. termination
40
Q

Initiation:

A

mRNA binding, start codon selection, binding the first aminoacyl-tRNA

41
Q

Elongation:

A

sequential addition of amino acids as specified by the codons in the mRNA

42
Q

Termination:

A

release of the completed polypeptide in response to a stop codon

43
Q

What is a fidelity function?

A

small subunit rRNA validates H-bonds and if they’ve not formed between all three base pairs, the tRNA must be an incorrect match, and it is rejected

44
Q

Do ribosomes have a fidelity function?

A

yes

45
Q

3 steps of elongation:

A
  1. codon recognition - aminoacyl-tRNA entry into the A-site)
  2. peptide bond formation(met is linked to Pro in A-site)
  3. translocation(simultaneously, the free tRNA is moved to the E-site, the peptidyl-tRNA is moved to the P-site)
46
Q

Is elongation a repeated process?

A

yes

47
Q

What marks the end of translation?

A

stop codons

48
Q

What are stop codons recognised by?

A

protein release factors

49
Q

What do RRF(ribosome releasing factors) promote?

A

dissociation of the ribosomal subunits, tRNA and mRNA

50
Q

What are proteins made on?

A

polyribosomes

51
Q

What is a strand of mRNA with associated ribosomes called?

A

a polysome

Building the Organism (11 decks)

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