AQA GCSE Triplet code & protein synthesis(Biology)

Triplet code & protein synthesis

DNA stores genetic instructions in all living organisms.

A gene is a short length of DNA that codes for a protein.

Proteins do important jobs: enzymes, hormones, structural components (like collagen).

DNA Code: How It Works

DNA is made of four bases: A, T, C, G.

Every 3 bases on one of the strands of DNA will code for 1 amino acid. This is known as the triplet code.

You will need slightly more detail than this, but this will be covered in the protein synthesis section below.

Protein Synthesis

This is made up of two main stages:

1.Transcription (occurs in nucleus)

2. Translation (occurs in cytoplasm at the ribosome).

Transcription

A section of DNA within a chromosome, known as a gene is used to produce a template molecule(also known as mRNA).

Once the template molecule is complete, it will leave the nucleus via the nuclear pore and enter the cytoplasm.

Stage 1 – The DNA is in the nucleus

Stage 2 The gene (part of DNA) unwinds, the template molecule shown in red is produced, using one of DNA strands

Stage 3 The DNA winds back up and the template molecule leaves the nucleus via the nuclear pore.

Translation

Proteins are synthesised on ribosomes, according to a template. Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order.

Stage 1

The template(mRNA) will attach to the ribsome. Carrier molecules with a specific amino acid attached will bind to the template in the ribosome.

The bases on the carrier molecules are complementary to the bases on the template.

Stage 2

The two carrier molecules are next to each other in the ribosome

Stage 3

A bond forms between the two adjacent amino acids at the ribosome

Stage 4

Ribosome moves along the template by 3 bases. The first carrier molecule leaves to collect another amino acid.

Its amino acid (red circle) stays attached.

The next carrier molecule will enter the ribosome and the process will continue until the protein chain is formed.

Folding of the protein

When the protein chain is complete it folds up to form a unique shape. This unique shape enables the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen.