Types of Protein

Function of fibrous and globular proteins

fibrous: support and structure

globular: metabolic

Amino acid sequence of fibrous and globular proteins

fibrous: limited number of amino acids, highly repitive sequence

globular : irregular or varied sequence

Structure of fibrous and globular proteins

fibrous: many only have secondary ; tertiary and quaternary rare

globualr: all have tertiary sequence

arrangement of polypeptide chains of fibrous and globular

fibrous: long parallel strands of fibers

globular: complex folding into a compact , spherical shape

relative stability of fibrous and globular

fibrous: more stable

globular: less stable

solubility of fibrous and globular

fibrous: insoluble (hydrophobic R groups on exterior)

globular: soluble (hydrophilic R groups on exterior ; hydrophobic R groups point inwards)

Examples of fibrous and globular proteins

fibrous: collagen, keratin, myosin , actin(myosin and actin found in skeletal muscles)

globular : enzymes , some hormones, haemoglobin, antibodies

What is in collagen

fibrous protein found in animal connective tissue : insoluble and very tough

Primary structure in collagen

• long unbranched polypeptide chains

• every 3rd amino acid is glycine

• high proportion of proline and hydroxproline

secondary structure of collagen

• chain coils to form a helix

• chains pack closely ( small amino acids)

tertiary structure of collagen

• chains do not fold so collagen does not have a true tertiary structure

quaternary structure of collagen

• 3 chains lie parallel and wind round each other : triple helix: tropocollagen

• chains held together by hydrogen bonds - triple helix : high tensile strength

What is haemoglobin

globular protein that transports oxygen by binding to oxygen and delivering it to cells aroudn the body , transported to the cells through the blood plasma

Primary structure of haemoglobin

• 2 different polypeptide chains - alpha and beat in adults

Secondary structure of haemoglobin

• lots of alpha helices

Tertiary structure

• highly folded —→ compact (storage in cell)

• many hydrogen and ionic bonds

• hydrophobic R groups sheltered on the interior and hydrophilic ones projected outwards → soluble

Quaternary groups of haemoglobin

association of 2 alpha and 2 beta chains , each w a heam group at the centre

Structures in protein

Primary, secondary, tertiary, quaternary

Types of protein in collagen and haemoglobin

collagen: fibrous

haemoglobin: globular

Main function of collagen and haemoglobin

collagen: connective tissue

haemoglobin: oxygen transport

amino acid variation of collagen and haemoglobin

collagen : repititive- every 3rd amino acid is glycine

haemoglobin: variable

Number of polypeptide chains in collagen and haemoglobin

collagen: 3

haemolgobin: 4

shape of collagen and haemoglobin

collagen: helical

haemoglobin: spherical

Prosthetic group of collagen and haemoglobin

collagen: no prosthetic group

haemoglobin: has a prosthetic group ( haem)