Fibrous Proteins (OCR A Level Biology)

• Fibrous proteins are long strands of polypeptide chains that have cross-linkages due to hydrogen bonds
• These proteins have little or no tertiary structure
• Due to a large number of hydrophobic R groups, fibrous proteins are insoluble in water
• Fibrous proteins have a limited number of amino acids with the sequence usually being highly repetitive
• The highly repetitive sequence creates very organised structures that are strong and this along with their insolubility property, makes fibrous proteins very suitable for structural roles
• Examples of fibrous proteins:
  • Keratin makes up hair, nails, horns and feathers (it is a very tough fibrous protein)
  • Elastin is found in connective tissue, tendons, skin and bone (it can stretch and then return to its original shape)

  • Collagen is a connective tissue found in skin, tendons and ligaments

Globular and fibrous protein models illustrating the roughly spherical shape of globular proteins and the long, stranded shape of fibrous proteins

Comparison of Globular & Fibrous Tertiary Proteins Table

Collagen

• Collagen is the most common structural protein found in vertebrates
• It provides structural support
• In vertebrates it is the component of connective tissue which forms:
  • Tendons
  • Cartilage
  • Ligaments
  • Bones
  • Teeth
  • Skin
  • Walls of blood vessels
  • Cornea of the eye

• Collagen is an insoluble fibrous protein

Function & properties of collagen

• Collagen is a flexible structural protein forming connective tissues
• The presence of many hydrogen bonds within the triple helix structure of collagen results in great tensile strength. This enables collagen to be able to withstand large pulling forces without stretching or breaking
• The staggered ends of the collagen molecules within the fibrils provide strength
• Collagen is a stable protein due to the high proportion of proline and hydroxyproline amino acids. These amino acids increase stability as their R groups repel each other
• The length of collagen molecules means they take too long to dissolve in water (making it insoluble in water)

Comparison between Collagen & Haemoglobin Table