n) o) Globular and Fibrous proteins

Fibrous proteins are strong so...

....so provide structural roles

Properties of Fibrous proteins

Insoluble in water

Very strong and tough

Why are fibrous proteins insoluble in water?

Contains a high proportion of amino acids with hydrophobic R groups

Why are fibrous proteins very strong and tough?

Due to many cross bridges between polypeptide chains

Examples of fibrous protein

Keratin

Elastin

Collagen

Keratin

Hair and nails

The more disulphide bridges in the keratin, the stronger it is

Elastin

Alveoli

Recoils after being deformed

Collagen

Skin

Flexible but doesn't stretch

Properties of globular proteins

- Compact, 3D globular shape

- Soluble in water

- Conjugated proteins have a prosthetic group

Why are globular proteins soluble in water?

They have amino acids with hydrophobic R groups orientate to the inside of the protein

It means they can be easily transported around organisms and be involved in metabolic reactions

What is a prosthetic group?

A non protein component that is tightly or permanently bound to the enzyme

Examples of globular proteins

Haemoglobin (conjugated protein)

Insulin

Catalase (conjugated protein)

Haemoglobin

- Conjugated Protein

- Can change shape

- Quaternary structure with 4 polypeptide chains. These chains are globin proteins, with 2 α-globins and 2 β-globins

- The 4 globin subunits are held together with disulphide bonds, arranged so that the hydrophobic R-groups face inwards and vice versa

- Each globin subunit has a prosthetic haem group containing Fe²⁺

Insulin

- Specific fixed shape

- Consists of 2 polypeptide chains, held together by 3 disulphide bridges

Catalase

- Conjugated protein

- Specific fixed shape

- Intracellular enzyme