Translation

Question 1

Who compiled a list of all the amino acids and how many of them were they and how many bases

Answer 1

• 20 amino acids
• 4 bases
  Thus the number of possible combinations with 4 bases and 20 amino acids are 64

Bases in triples = 4^3 making 64 amino acids with some redundancy
- therefore the genetic code must be at least triplet bases —> TRIPLET CODON HYPOTHSIS

Question 2

Key features of the genetic code include:

Answer 2

• 61 of a possible 64 codons specify an amino acid
• most amino acids have more then one codon
• three codons specify stop (UAA, UAG, UGA)
• one codon specifies start (AUG - this codon also specifies methionine

Question 3

Codon definition

Answer 3

• a triples that encodes one amino acid

Question 4

tRNA make-up

Answer 4

• single strand of RNA
• 70 - 80 nucleotides in length
• at least one tRNA for each amino acid
• each tRNA has a region which can bind an amino acid AND a region which can interact with mRNA

Question 5

3 important features of tRNA

Answer 5

1. tRNA as an adaptor molecule must be able to bind an amino acid - (Amino acid binding site - triplet)
2. Must be able to interact with mRNA as well - (RNA binding site) - there are triplet codons that code for amino acids - on the tRNA the complimentary nucleotides are called anticodons
   ANTICODON - A PART OF THE TRNA THAT DIRECTLY INTERACTS WITH MRNA
3. It’s 3D structure - it’s particular shape fits perfectly on the ribosomes

Question 6

How to attach amino acid onto corresponding tRNA
STEPS INVOLVED IN ‘CHARGING’ A tRNA

Answer 6

An enzyme recognises both a specific amino acid and the correct tRNA for this amino acid and joins them together
There are 20 different charging enzymes - one for each amino acid

1. Amino acid and tRNA enter active site
2. Using ATP, covalent bonds are catalyses between amino acid and its tRNA
3. Charged tRNA is released

Question 7

Translation definition

Answer 7

• translation is the synthesis of proteins by ribosomes using mRNA as a set of instructions
• ribosomes contain both ribosomal RNA (rRNA) and proteins

Question 8

Anatomy of the ribosome

Answer 8

LEARN PICTURES
- Consists of two parts:
- small subunit - where mRNA binds
- large subunit - 3 pockets EPA sites
A - where amino acids arrive
P - peptide site (where the growing polypeptide chain grows
E- exit

Tunnel above P site is important as some proteins are hundreds or thousands of amino acids in length, as amino acids are added one by one, they are Abel to wiggle out of the tunnel

Question 9

Three stages of translation

Answer 9

Initiation
Elongation
Termination

(All three stages require energy input)

Question 10

Process of initiation

Answer 10

• a specific initiation tRNA (carrying methionine) binds to the small ribosomal subunit
• the small ribosomal subunit/ initiator tRNA identifies the 5’ G-cap and attaches to the mRNA
• the small ribosomal subunit/initiator tRNA complex moves along the mRNA (5’ to 3’ direction) until it finds the initiation AUG codon
• the complex stops, with the initiator tRNA carrying the first methionine positioned in the P site
• the large ribosomeal subunit attaches

Question 11

Elongation

Answer 11

1. A ‘charged; tRNA, with an anticodon complementary to the A site codon, lands in the A site
2. Then two things happen at the same time
   • the ribosome will break the bond that binds the amino acid to the tRNA in the P site, transfer the amino acid to the newly arrived amino acid (attached to the tRNA and the A site) and form a peptide bond between them

Not finished cue card!!!