Protein translation

Question 1

Start codon

Answer 1

Sequence: AUG (adenine, uracil, guanine)

Function: Marks the beginning of a protein-coding sequence in mRNA.

Question 2

Stop codon

Answer 2

Sequences: UAA (ochre), UAG (amber), UGA (opal)

Function: Signals the termination or end of protein synthesis.

Question 3

Initiation in protein translation
Step 1

Answer 3

The small ribosomal subunit binds to the mRNA molecule at the start codon (AUG).

Initiator tRNA, carrying the amino acid methionine pairs with the start codon.

Question 4

Elongation in protein translation
Step 2

Answer 4

The ribosome travels along the mRNA, reading the code in the 5’ to 3’ direction.

tRNA Binding:
Special tRNA helpers bring specific amino acids and stick to the mRNA code using matching pairs.

Building the Chain:
With the ribosome’s help, amino acids join together, forming the growing protein chain.

Moving Forward (Translocation):
The ribosome moves forward to the next part of the mRNA code.
The helper tRNA that delivered its amino acid leaves, and a new tRNA with the next amino acid comes in.

Question 5

Termination in protein translation
Step 3

Answer 5

The process continues until a stop codon (UAA, UAG, or UGA) is reached.

Release factors recognize the stop codon, causing the release of the completed polypeptide chain from the ribosome.