Translation

Question 1

what is translation?

Answer 1

• RNA-directed synthesis of a polypeptide

- message in mRNA is interpreted by tRNA

Question 2

where does tRNA get amino acids from? where does it transfer them to?

Answer 2

from the cytoplasm to the ribosome (location of polypeptide formation)

Question 3

what are the three stages of translation?

Answer 3

1. Initiation
2. Elongation
3. Termination

Question 4

what happens during initiation stage of translation?

Answer 4

mRNA, tRNA with first amino acid (Met), and the two ribosomal subunits are all brought together to form initiation complex

Question 5

how does initiation complex bind together? where does mRNA bind? where does tRNA bind, what does this establish?

Answer 5

1. mRNA binds to the small ribosomal subunit near it’s 5’ end
2. tRNA binds to start codon on mRNA
   - establishing reading frame
3. Large ribosomal subunit binds to complex, completing Translation initiation complex

Question 6

what happens during elongation stage? which direction does ribosome move along mRNA?

Answer 6

• Amino acids are added one by one to polypeptide.

- moves along the mRNA from 5’ to 3’

Question 7

what are the three steps in elongation cycle?

Answer 7

i. Codon Recognition
ii. Peptide Bond Formation
iii. Translocation
Ribosome moves down 3 bases
(one codon)

Question 8

what happens during codon recognition step?

Answer 8

• anticodon of incoming tRNA base-pairs with complementary mRNA codon in A site

Question 9

what happens during peptide bond formation step?

Answer 9

• Bond is formed between incoming amino acid and growing polypeptide chain (energy requiring)
• Polypeptide chain transferred to tRNA in A site

Question 10

what happens during translocation step?

Answer 10

• Ribosome moves down 3 bases (one codon)
• Empty tRNA released from E site (energy releasing)
• tRNA with polypeptide chain moves into P site
• Next codon to be translated moves into A site
• Ribosome ready for next tRNA

Question 11

how long does elongation stage continue for?

Answer 11

Steps are repeated until the STOP codon reaches A site

Question 12

what happens during termination stage of translation?

Answer 12

• Stop codon reaches the A site of the ribosome
• Release Factor binds to the stop codon
• Hydrolyses bond (adds water to bond) holding polypeptide to tRNA –> Completed polypeptide is released
• Small and large subunits of ribosome separate and mRNA is released