What are the two categories of proteins? Give three examples of each.

  1. Globular proteins - examples include haemoglobin, insulin and amylase
  2. Fibrous proteins - examples include keratin, collagen and elastin

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What are the characteristics of globular proteins?

Globular proteins are compact, spherical, and soluble.

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What are the 3 types of prosthetic groups found in globular proteins?

Lipids, carbohydrates, and metal ions.

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What is the function of haemoglobin?

Haemoglobin is used to carry oxygen around the body in red blood cells.

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What is the quaternary structure of haemoglobin?

Haemoglobin is made up of 4 polypeptide chains.

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Which characteristic allows haemoglobin to carry 4 oxygen molecules at once?

It is made up of four polypeptide chains, each containing a haem prosthetic group with an iron atom that binds to oxygen.

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What is the structure and function of insulin?

Insulin is made up of two polypeptide chains held together by disulfide bonds.


Insulin is used to regulate blood glucose concentration.

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What is the structure and function of amylase?

Amylase is made up of a single polypeptide chain folded into both alpha-helixes and beta-pleated sheets.


Amylase is used to break down starch into maltose.

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What is the function of collagen?

Collagen is used as a structural component in skin, tendons, cartilage, bones, teeth, and blood vessels.

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How many polypeptide chains make up collagen?

Collagen is made up of 3 polypeptide chains.

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Where is keratin found?

Keratin is found in the hair, skin, and nails.

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Which amino acid allows disulfide bonds to form in keratin?

The amino acid cysteine, which contains the element sulphur.

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What determines the flexibility or rigidity of keratin?

The number of disulfide bonds it contains.

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What is elastin?

Elastin is a fibrous protein found in elastic connective tissue. 

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Give 3 examples of metabolic roles of globular proteins.

  1. Enzymes
  2. Hormones
  3. Antibodies

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