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NUT1004 > Translation > Flashcards

Translation Flashcards

1
Q

What are the three key types of RNA involved in protein synthesis

A

mRNA, tRNA, rRNA

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2
Q

Which end of tRNA is the AA attached to

A

3’ end

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3
Q

What is an anticodon

A

Feature of tRNA which is three bases that pair with a complementary codon on mRNA

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4
Q

How much of total cell RNA does rRNA account for

A

80%

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5
Q

How many strands of rRNA does the large subunit of the ribosome consist of and what are their sizes

A

3 strands, 28S, 5.8S, 5S

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6
Q

How many protein molecules are in the large subunit of the ribosome

A

49

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7
Q

How many protein molecules are in the small subunit of the ribosome

A

33

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8
Q

How many strands of rRNA does the small subunit of the ribosome consist of and what are their sizes

A

1 strand, 18S

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9
Q

What is the size difference between the large and small subunit of the ribosome

A

60S vs 40S

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10
Q

What are the two main functions of rRNA

A

Maintain ribosome form and catalyse peptide bond formation in protein translation

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11
Q

Define the genetic code in mRNA

A

The way in which the sequence of the four bases in mRNA correspond to the sequence of the 20 amino acids in proteins

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12
Q

What are triplets

A

Bases are in trios called codons

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13
Q

What is meant by no overlap in the genetic code

A

Each codon relates to one amino acid

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14
Q

What are the 6 features of the genetic code

A

One directional (5’-3’), no ‘punctuation’/modification in sequence, degenerate, no overlap, designated STOP codons, universal

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15
Q

How many codons code for amino acids

A

61

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16
Q

How many codons are STOP codons

A

3

17
Q

What is the designated start codon and what does it code for

A

AUG- methionine

18
Q

What is meant by degenerate

A

Most amino acids are encoded by more than one codon as there are more codons than amino acids

19
Q

Which two amino acids only have one codon

A

Tryptophan and methionine

20
Q

What are Aminoacyl tRNA synthetases

A

Enzyme that catalyses the aminoacetylation of tRNA

21
Q

What are the 4 steps of aminoacetylation of tRNA

A

1) AAs attached to specific tRNA
2) AA I’d esterified and activated so it can form a peptide bond
3) tRNA+AA= aminoacyl tRNA (catalysed by aminoacyl tRNA synthetase and use of energy from ATP)
4) the AA in aminoacyl tRNA will be incorporated into a growing polypeptide at a posterior determined by it’s anticodon on tRNA

22
Q

What are the 4 steps of translation initiation

A

1) small ribosomal subunit joins with special initiator tRNA carrying methionine (so anticodon matches AUG start codon on mRNA)
2) attaches to cap structure at 5’ end of mRNA and scans for AUG start codon
3)At the start codon the large subunit binds to them to form the initiation complex
4) the special initiator tRNA occupies the P (peptidyl) binding site of the ribosome

23
Q

What are the 4 steps of translation elongation

A

1) second aminoacylated tRNA enters A (aminoacyl) binding site of ribosome, it,s anticodon matches the mRNA codon at the A site
2) peptide bond is formed between the two adjacent AAs, initiator tRNA releases it’s AA (Met) onto the new tRNA
3)Ribosome shifts along the mRNA to the next codon (now deacylated) and the initiator tRNA is at the E (exit) binding site of the ribosome where it exits
4) another aminoacylated tRNA enters the A site of the ribosome and another peptide bond is formed (cycle repeats)

24
Q

What are the 4 steps of translation termination

A

1) mRNA STOP codon enters A site
2) no tRNAs can match STOP sequence so no tRNA approaches A site
3) release factor binds to codon instead, leading to the breaking of the bond linking tRNA and the polypeptide
4) polypeptide is released from the ribosome and disassociates into it’s subunits until it is required again

25
Q

Where does post translational modification occur

A

Endoplasmic reticulum

26
Q

What 3 ways can proteins be modified post translation

A

Folding, formation of disulphide bonds, glycosation

27
Q

What is glycosation

A

Addition of sugar group to form a glycoprotein

28
Q

What are the 5 steps of post translational modification

A

1) signal sequence emerges from ribosome and is recognised by a signal recognition particle (SRP) which binds to it, stopping elongation of a polypeptide
2) SRP brings the entire ribosome and incomplete polypeptide to join with a peptide translocation complex on the outer ER surface
3)SRP disassociates itself from ER surface and elongation resumes with the polypeptide being fed from ribosome into ER until complete
4)signal sequence is removed by signal peptidase in ER lumen
5)PP now free in ER lumen, ribosome disassociates and is recycled

29
Q

Does post translational modification happen to all proteins

A

No, some remain in the cytoplasm while others are transferred to the ER for PTM

NUT1004 (14 decks)

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