translation

Question 1

what are 2 important components for translation

Answer 1

• mRNA
  -tRNA

Question 2

What are codons

Answer 2

Series of 3 nucleotides in mRNA that code for an amino acid
- direct the placement of specific amino acids into a protein

Question 3

What are the 3 stop codons

Answer 3

• UAA
  -UAG
• UGA

Question 4

What is the start codon

Answer 4

AUG

Question 5

What are 4 important components for translation

Answer 5

• mRNA
• tRNA
• Amino acids
• ribosomes

Question 6

Describe initiation in translation

Answer 6

• small ribosome subunit attaches to mRNA (in prokaryotes attaches at recognition sequence AGGAGG, in eukaryotes at 5’ GTP cap)
• subunit then moves along until it reaches the start codon AUG
• methionine charged RNA with complementary anticodon sequence UAC binds to start codon = first amino acid is methionine
• ribosome large subunit joins initiation complex, methionine charged tRNA occupies the P site (polypeptide) while the A site (anticodon) is aligned with the next mRNA codon

Question 8

Describe elongation in translation

Answer 8

• anticodon of an incoming tRNA binds to the codon at the A site of ribosome
• the next amino acid is linked to methionine by peptidyl transferase which breaks bond between amino acid + its tRNA in P site and forms bond between amino acid and amino acid attached to its tRNA in A site
• free tRNA is moved to E site (exit) and is released, ribosome moves along to next codon and the growing polypeptide chain moves to P site

Question 9

Describe termination in translation

Answer 9

• a release factor binds to the complex when a stop codon enters the A site
• the release factor disconnects the polypeptide from the tRNA in the P site
• remaining components separate

Question 10

What are 3 processes which modify polypeptide chains after translation

Answer 10

• proteolysis
• glycosylation
• phosphorylation

Question 11

Describe proteolysis

Answer 11

cutting the polypeptide allowing it to fold into different shapes

Question 12

Describe glycosylation

Answer 12

Addition of sugars to polypeptide, which is important for targeting + recognition
- catalysed by enzymes in the ER + golgi apparatus

Question 13

Describe phosphorylation of polypeptides after translation

Answer 13

Addition of phosphate groups alter the shape of a protein
- catalysed by protein kinase