Week 3: Translation and the genetic code

Question 1

Which two scientists cracked the genetic code and what were their findings?

Answer 1

Sydney Brenner and Francis Crick
- they found that there must be 3 nucleotides per amino acid
- realised that the code must be degenerate

Question 2

What are ribosomes?

Answer 2

• the site of translation
• large complexes of 4 RNA and over 80 proteins

Question 3

Describe step one of translation: initiation (3 pts)

Answer 3

• in eukaryotes it begins at the most 5’ AUG codon, where the small subunit binds and then moves to the start codon (methionine)
• this allows large subunit to bind = ribosome
• p-site is filled with tRNA and A-site is empty

Question 4

Describe step two of translation: elongation (3 pts)

Answer 4

• the tRNA with the complementary anticodon to the A-site’s codon binds
• empty tRNA moves to the exit site to be released
• there is a peptidyl tRNA in the A-site

Question 5

Describe step three of translation: termination (2 pts)

Answer 5

• tRNAs cannot bind with stop codons so termination factors bind there instead
• the polypeptide is released and the subunits are disassembled

Question 6

What are the two types of substitution mutations?

Answer 6

• transitions: interchanges of purines or pyrimidines
• transversions: changes of a purine FOR a pyrimidine or vice versa

Question 7

What are the different regions that mutations can effect and how do they do this?

Answer 7

• intergenic region: no phenotypic effect but can have genotypic effect
• non-coding regions: may be silent or effect gene expression
• coding regions: have various effects