Fibrous Proteins | A-level Biology | OCR, AQA, Edexcel

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The key points covered in this video include:

1. Fibrous Proteins
2. Collagen
3. Structure of Collagen
4. Keratin
5. Elastin

Fibrous Proteins

The 3D tertiary and quaternary structure of proteins can also result in the formation of fibrous proteins. Fibrous proteins have some similar properties to each other: They contain long polypeptide chains with repeating sequences of amino acids, The amino acids have non-polar R groups so the proteins are insoluble in water, The polypeptide chains are able to form fibres which make the proteins stronger. A fibrous protein is a very long, strong and insoluble protein which often has a structural role in organisms.

Collagen

Collagen forms very strong fibres and so is used to provide strength to many parts of the body: Collagen is found in artery walls to prevent vessels from bursting from high pressure, Collagen is used to make tendons which connect muscles to bone, allowing the skeleton to move, Collagen is also used to make bone.

Structure of Collagen

Collagen has such enormous strength as the polypeptide chains assemble into stronger fibres. A collagen molecule is composed of three polypeptide chains - it has a quaternary structure. Each polypeptide chain is up to 1000 amino acids long with a repeating primary structure. The three polypeptide chains wrap around each other in a triple helix to form a collagen molecule. Many collagen molecules cross-link to other collagen molecules to form a fibril. Many fibrils then assemble into a stronger collagen fibre.

Keratin

Keratin is another example of a fibrous protein that is very hard and strong. Keratin is therefore used for hard body parts such as fingernails, horns and hooves. The primary structure of keratin contains high amounts of cysteine - an amino acid containing sulphur. This results in disulphide links forming between the two polypeptide chains which makes the molecule very hard and strong.

Elastin

Elastin is a final example of a fibrous protein which has elastic properties - it can stretch and recoil. Elastin is stretchy due to coiling of the elastin molecules and cross-links that keep the molecules together. Elastin is found in lungs to help them inflate and deflate during ventilation. Elastin is also found in our bladder to help it expand to hold urine. Elastin is found in blood vessel walls where it helps maintain blood pressure by stretching and recoiling.

Summary

Fibrous proteins are very long, strong and insoluble, with a structural role in organisms
Collagen is a fibrous protein which is used to strengthen tendons, bones and artery walls
A collagen molecule is composed of three polypeptide chains twisted into a triple helix
Many collagen molecules can cross-link to form a stronger collagen fibril
Many collagen fibrils can then bundle together to form a very strong collagen fibre