U4L3 - translation

Question 1

What is translation?

Answer 1

It is the synthesis of protein from an mRNA template (i.e. translating the info coded in mRNA to a protein)
mRNA → Protein (facilitated by transfer RNA molecules =tRNA)

Question 2

Where does translation happen?

Answer 2

Happens in a ribosome, in the cytoplasm

Question 3

What are the three stages?

Answer 3

Initiation
Elongation
Termination

Question 4

Explain “the genetic code”

Answer 4

• A specific amino acid coded for by particular RNA (or complementary DNA) bases is determined by the genetic code.
• The four RNA bases (A, U, G, C) must be used in combinations of at least three to code for 20 amino acids

Question 5

What is a codon?

Answer 5

CODON = a group of three base pairs that code for an amino acid
Start Codon = initiates translation
Stop Codon = signals termination of translation

Question 6

Explain tRNA structure

Answer 6

tRNA has regions that base pair with themselves resulting in cloverleaf pattern

Anticodon – 3 nucleotide sequence that pairs with a codon in an mRNA

Codon – 3 nucelotide sequence on mRNA

At the other end, is a region that carries the amino acid that corresponds to the anticodon

Question 7

Explain the ribosome

Answer 7

It is made up of 2 subunits and has three tRNA sites (A site – acceptor site
P site – peptide site
E site – exit site)
- Ribosomes join amino acids in ordered sequence to make polypeptide chains!

Question 8

What happens during initiation?

Answer 8

• Ribosome small subunit recognizes and binds to 5’ cap upstream of AUG sequence
• Initiator tRNA recognizes start codon AUG (corresponds to amino acid methionine)
• Ribosome large subunit attaches to complete translational complex

Question 9

What happens during elongation?

Answer 9

• 1st tRNA enters the ribosome at the P site, bringing an amino acid along with it (AUG = methionine)
• The next tRNA comes into the A-site
• Peptide bonds are formed between the P-site and A-site (via peptidyl transferase)
• tRNAs move to the E-site, where they exit

Question 10

Explain what happens during termination

Answer 10

• When a stop codon (UAA, UAG, or UGA) is encountered by the ribosome, there is no corresponding amino acid for that stop codon
• A release factor dismantles the ribosome/mRNA complex, releasing the polypeptide