AS level. B.4 Fibrous and globular proteins (introduction video)
What are the two basic types of proteins?
Globular proteins and Fibrous proteins.
What kind of functions does fibrous proteins have?
What kind of functions does globular proteins have?
Describe the structure of a fibrous protein
They are formed from 3 parallel polypeptide chains (each forming their own helix structure) held together by cross-links. They are insoluble and have a high tensile strength. Primary structure is made from repeat units of amino acids. They form unbranched polypeptide chains.
What are some examples of fibrous proteins?
What is collagen?
It is the connective tissue found in the skin, tendons, ligaments and the nervous system. They are made up of three polypeptides wound together in a strong and flexible rope like structure.
What is keratin?
Keratin is in hard structures such as hair, skin, nails, claws and hooves. Many of its amino acids contain sulfur which enable many disulfide bonds to form (disulfde bridges). Keratin is strong, insoluble and, depending on how many disulfide bridges, flexible (the more disulfide bonds, the less flexible).
What is elastin?
Found in elastic fibrous inside the walls of blood vessels and alveoli. They allow these structures to expand and to recoil to their normal size. It is a quaternary protein made from molecules called tropoelastin.
What is elastin made from?
Many molecules called tropoelastin
Describe the shape of globular proteins
They are compact and spherical in shape. Any hydrophobic R-groups are kept away from water. The hydrophilic R-groups are kept on the outside of the protein (making it soluble in water).
What are some examples of globular proteins?
Describe the structure of haemoglobin
Has 4 polypeptide chains; so is a quaternary protein. contains 2 alpha and 2 beta sub-units. Each sub-unit contains a prosthetic haem group. Inside the haem groups are iron ions.
What happens to fibrous proteins as they become denatured?
They lose their strength
What happens to globular proteins when they become denatured?
They become insoluble and inactive.
What is the role of insulin?
It is a hormone that regulates blood glucose concentration
Describe the structure of insulin
It is soluble in water and maintains a specific shape in order to fit into specific receptors on cell-surface membranes
Some proteins contain a prosthetic group (such as haem). What are these proteins called?
What do you call proteins that do not contain a prosthetic group?
What is the function of catalase?
It is an enzyme that speeds up the rate of a reaction.
Describe the structure of catalase
It is a quaternary protein that contains 4 haem prosthetic groups (this allows it to interact and speed up the breakdown of hydrogen peroxide)