Types Of Protein Flashcards
Globular proteins
Globular proteins are compact, water soluble, and usually roughly spherical. Formed when proteins fold into tertiary structure in such a way that the hydrophobic R-groups on the amino acids are kept away from the aqueous environment. The hydrophilic R-groups are on the outside of the protein. This means the proteins are soluble in water.
Solubility means they are essential for regulating many of the processes necessary to life like chemical reactions and immunity.
Insulin
Is a globular protein. Is a hormone involved in the regulation of blood glucose concentration. Hormones are transported in the bloodstream so need to be soluble. Hormones also have to fit into specific receptors on cell-surface membranes to have their effect and therefore need to have precise shapes.
Conjugated proteins
Globular proteins-contain a non-protein component called a prosthetic group. Proteins without prosthetic groups are called simple proteins.
Different types of prosthetic groups- lipids or carbohydrates can combine with proteins forming lipoproteins or glycoproteins. Metal ions and molecules derived from vitamins also form prosthetic groups.
Haem groups are examples of prosthetic groups. They contain an iron ion (Fe2+). Catalase and haemoglobin both contain haem groups.
Haemoglobin
Red, oxygen-carrying pigment found in red blood cells. It is a quaternary protein made from four polypeptides, two alpha and two beta subunits. Each subunit contains a prosthetic haem group. The iron(II) ions present in the haem groups are each able to combine reversibly with an oxygen molecule. This is what enables haemoglobin to transport oxygen around the body. It can pick up oxygen in the lungs and transport it to the cells that need it, where it is released.
Catalase
Catalase is an enzyme. Quaternary protein containing four haem prosthetic groups. The presence of the iron(II) ions in the prosthetic groups allow catalase to interact with hydrogen peroxide and speed up its breakdown. Hydrogen peroxide is a common byproduct of metabolism but is damaging to cells and cell components if allowed to accumulate. Catalase makes sure this doesn’t happen.
Fibrous proteins
Formed from long, insoluble molecules. This is due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structures. They contain a limited range of amino acids, usually with small R-groups. The amino acid sequence in the primary structure is usually quite repetitive. This leads to very organised structures reflected in the roles fibrous proteins often have. Keratin, elastin, and collagen are examples of fibrous proteins.
Fibrous proteins tend to make strong, long molecules which are not folded into complex three-dimensional shapes like globular proteins.
Keratin
Group of fibrous proteins present in hair, skin and nails. Large proportion of the sulfur-containing amino acid, cysteine. This results in many strong disulfide bonds (disulfide bridges) forming strong, inflexible, and insoluble materials. The degree of disulfide bonds determines the flexibility. The degree of disulfide bonds determines the flexibility- hair contains fewer bonds making it more flexible than nails, which contain more bonds. The unpleasant smell produced when hair or skin is burnt is due to the presence of relatively large quantities of sulfur in these proteins.
Elastin
Fibrous protein found in elastic fibres (along with small protein fibres) Elastic fibres are present in walls of blood vessels and alveoli of lungs-they give these structures the flexibility to expand when needed, but also to return to their normal size. Elastin is a quaternary protein made from many stretchy molecules called troploelastin.
Collagen
Fibrous protein. Is a connective tissue found in skin, tendons, ligaments and nervous system. Number of different forms but all made up of three polypeptides wound together in a long and strong rope-like structure. Like rope, collagen has flexibility.
