Classification of proteins

Question 1

How do we classify proteins ?

Answer 1

• Based on structure
• Based on composition
• Based on functions

Question 2

Classification based on structure

Answer 2

• Fibrous proteins
• Globular proteins
• Intermediate proteins

Question 3

Classification based on composition

Answer 3

• Simple Proteins
• Conjugated proteins

Question 4

Classification based on functions

Answer 4

• Structural
• Enzymes
• Hormones
• Respiratory pigments
• Transport proteins
• Contractile proteins
• Storage proteins
• Immunoglobulins
• Toxins

Question 5

Fibrous Proteins

Answer 5

• Linear
• Tough & strong
• Long parallel polypeptide chains cross linked at regular intervals
• Perform structural functions in the cells
• Usually do not have a (complex) tertiary structure
• Insoluble in water
• Most important structure: secondary structure

Question 6

Examples of fibrous proteins

Answer 6

• Collagen
• Elastin
• Myosin
• Keratin
• Silk

Question 7

Globular proteins

Answer 7

• Spherical/globular shape
• Polypeptide chain tightly folded into spherical shapes
• Physically softer
• Most proteins in cells are globular proteins
• Function: form enzymes, antibodies and some hormones
• Readily soluble in water
• Most important structure: Tertiary Structure

Question 8

Examples of globular proteins

Answer 8

• insulin
• hemoglobin
• albumin
• DNA polymerase and RNA polymerase

Question 9

Intermediate proteins

Answer 9

• Intermediate shape more or less linear
• Soluble in water

Question 10

Example of intermediate protein

Answer 10

Blood clotting proteins

Question 11

Simple proteins

Answer 11

• Composed of only amino acids, relatively simple structure

Question 12

Examples of simple proteins

Answer 12

• Myosin
• Collagen
• Keratin
• Insulin

Question 13

Conjugated proteins

Answer 13

• Complex, contains one or more non-amino acid component called prosthetic groups, essential for biological function.
• Usually globular and soluble in water
• Most enzymes are conjugated proteins
• Further classification based on the nature of the prosthetic groups