3.7 - Types of Protein

Question 1

What are the 2 main types of protein?

Answer 1

Globular

Fibrous

Question 2

What are the features of globular proteins?

Answer 2

Compact - highly folded to form globular shape

Usually roughly spherical in shape (not always e.g. hCG)

Water soluble -important for function

Question 3

How are globular proteins water soluble?

Answer 3

Upon tertiary structure folding the hydrophilic R groups assemble on the outside and hydrophobic on the inside.

Question 4

Give 3 examples of globular proteins.

Answer 4

Insulin

Haemoglobin and catalase (both conjugated)

Question 5

How does insulin being globular support its function?

Answer 5

• Needs to be water soluble to travel in the bloodstream
• Need to fit into specific receptors plasma membranes so they need specific shapes.

Question 6

What is a conjugated protein?

Answer 6

• Globular protein with prosthetic group (non-protein component)
• Proteins without prosthetic groups are simple proteins

Question 7

Describe the function and structure of haemoglobin.

Answer 7

• Used to transport oxygen, forms oxyhaemoglobin
• Has 4 polypeptide subunits - 2 ß subunits and 2 alpha
• It is conjugated, each subunit has a prosthetic groups
  
  • Prosthetic Group: haem group (Fe²⁺)
  • Oxygen attaches and dettaches to the haem

Question 8

Describe the structure and function of catalase.

Answer 8

• An enzyme responsible for breaking down hydrogen peroxide
  
  • byproduct of metabolism but is harmful to cells if accumulates
• Quaternary protein with 4 haem prosthetic groups
• Presence of Fe²⁺ allows catalase to interact with H₂O₂ and catalyse the breakdown.

Question 9

What are the features of fibrous proteins?

Answer 9

• Regular amino acid sequence
• Insoluble in water
• Strong, long
• Unreactive

Question 10

What are examples of fibrous proteins

Answer 10

Keratin Elastin Collagen

Question 11

Describe the features, functions and structure of keratin.

Answer 11

• 2 coiled polypeptide chains
• Present in hair, skin, nails
• Has many disulphide bonds making strong and flexible

Question 12

Describe the features, functions and structure of elastin.

Answer 12

• 4^o protein formed by linking tropoelastin fibres together
• Elastin found in airways, alveoli, skin and bladder wall
  
  • Allows for stretch and recoil

Question 13

Describe the features, functions and structure of collagen.

Answer 13

• 3 wound polypeptide chains in a rope structure
  
  • Not easily stretched
• Gives strength to artery walls
• Found in tendons, ligaments