Translation

Question 1

What are the stages of translation?

Answer 1

1. mRNA attaches to the small subunit of the ribosome at the start codon (AUG) and then the large subunit attached.
2. tRNA with complementary anticodon (UAC) brings the correct amino acid to the ribosome to line up with the start codon
3. Another tRNA brings the next amino acid which anticodon base pairs with the next codon on the mRNA.
4. A peptide bond is formed between the 1st and 2nd amino acid, catalysed by the enzyme peptidyl transferase
5. The ribosome moves along to cover the next codon and the 1st tRNA is released.
6. The next tRNA attaches and the process repeats so that a sequence of amino acids in the correct order is formed - the polypeptide.
7. When the ribosome reaches the last codon on the mRNA (the stop codon - UGA, UAA or UAG), the polypeptide is released (the stop codon binds to release factors which cause the ribosome to detach)
8. The amino acids are joined by peptide bonds by the ribosome, to give the primary structure of the protein which then folds into secondary, tertiary etc.

Question 2

What enzyme catalyses the formation of peptide bonds?

Answer 2

Peptidyl transferase

Question 3

Ho many different tRNAs are there?

Answer 3

20

Question 4

How many amino acids can a tRNA pick up?

Answer 4

1 specific amino acid

Question 5

What is the start amino acid?

Answer 5

Methionine

Question 6

What is the start codon?

Answer 6

AUG

Question 7

What do stop codons do?

Answer 7

The don’t put an amino acid in, they make the ribosome fall off

Question 8

What kind of genetic code is on DNA?

Answer 8

It is degenerate

Question 9

What does degenerate mean?

Answer 9

More than 1 codon can code for the same amino acd

Question 10

What is a triplet codon?

Answer 10

A sequence of 3 nucleotides and therefore 3 bases with each codon codes for a particular amino acid

Question 11

How is DNA code structured?

Answer 11

It is non-overlapping

Question 12

Why is DNA code non-overlapping?

Answer 12

The codons lie back-to-back along the gene and mRNA so they don’t overlap and each codon is transcribed and translated in tun, one by one, with no overlaps or gaps in between.

Question 13

What are the 3 types of mutation?

Answer 13

Base insertion, base deletion and base substitution

Question 14

What is base insertion?

Answer 14

A base is inserted

Question 15

What is base deletion?

Answer 15

A base is deleted

Question 16

What is base substitution?

Answer 16

A base is changed

Question 17

What do both base insertion and deletion cause?

Answer 17

A frame shift

Question 18

What is a frame shift?

Answer 18

Different amino acids are produced

Question 19

What does a ribosome have?

Answer 19

A binding site for both mRA and tRNA

Question 20

What is the importance of rRNA?

Answer 20

For stabilising the growing polypeptide chain and helps catalyse synthesis reaction when 2 amino acids join

Question 21

What does rRNA form?

Answer 21

Part of the catalytic area in the large subunit for the formation of the peptide bond