1.4: Proteins

Label the orange, green, and blue parts of this diagram

Write the wird equation for the formation of a dipeptide.

Peptide 1 + peptide 2 → dipeptide + water

Describe the process of dipeptide formation (4 marks)

• A condensation reaction (1 mark) between two amino acids (1 mark)

• Forms a peptide bond (1 mark) between amino acids

• Water is formed as a byproduct (1 mark)

Describe the opposite reaction (4 marks)

• Hydrolysing (1 mark) a dipeptide would involve the addition of water (1 mark)

• The peptide bond would be broken (1 mark)

• Two amino acids would be produced (1 mark)

What kind of reaction form a polypeptide?

Condensation polymerisation

What are proteins?

Proteins are polypeptide chains that have folded up into a specific 3D shape

What are the two shapes a protein can be?

1. Globular (metabolic finctions, e.g enzymes, receptor molecules, and transport proteins in plasma membranes)

2. Fibrous (structural, e.g keratin in our hair and collagen in connective tissue)

What is the primary structure of a protein?

The sequence of amino acids in a polypeptide (different for each protein)

What is the secondary structure of a protein?

• Either alpha helix of beta pleated sheet (only alpha helix on AQA spec)

• Maintained by hydrogen bonds (between N-H and C=O groups on different amino acids in a polypeptide chain)

What is the tertiary structure of a protein?

• A specific 3D shape (different for each protein)

• Maintained by bonds between R groups - including:

  • Hydrogen bonds (weak)

  • Ionic bonds

  • Disulphide bridges/bonds (covalent bonds)

What is the quaternary structure of a protein?

• Several polypeptides

• Maintained by bonds between polypeptides

  • Lots of hydrogen bonds (weak)

  • Ionic bonds

  • Disulphide bridges

• May be non-protein (prosthetic) groups. E.g haem groups in haemoglobin