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Types, Proteins classified by function, Function of proteins

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  1. 1. PROTEINS
  2. 2. PRIMARY STRUCTURE  Sequence of amino acids  Polypeptide chain Protein
  3. 3. SECONDARY STRUCTURE The folding of the N-C- C backbone of the polypeptide chain using weak hydrogen bonds Protein
  4. 4. SECONDARY STRUCTURE  This produces the alpha helix and beta pleating  The length of the helix or pleat is determined by certain amino acids that will not participate in these structures (e.g. proline) Protein
  5. 5. TERTIARY STRUCTURE The folding of the polypeptide into domains whose chemical properties are determined by the amino acids in the chain Protein
  6. 6. TERTIARY STRUCTURE  This folding is sometimes held together by strong covalent bonds (e.g. cysteine-cysteine disulphide bridge)  Bending of the chain takes place at certain amino acids (e.g. proline)  Hydrophobic amino acids tend to arrange themselves inside the molecule  Hydrophilic amino acids arrange themselves on the outside Protein
  7. 7. QUATERNARY STRUCTURE Some proteins are made of several polypeptide subunits (e.g. haemoglobin has four) Protein Kinase C Protein
  8. 8. QUATERNARY STRUCTURE  These subunits fit together to form the functional protein  Therefore, the sequence of the amino acids in the primary structure will influence the protein's structure at two, three or more levels Protein
  9. 9. Protein
  10. 10. PROTEIN FUNCTIONS  Protein structure determines protein function  Denaturation or inhibition which may change protein structure will change its function  Coenzymes and cofactors in general may enhance the protein's structure Protein
  11. 11. Fibrous proteins  Involved in structure: tendons ligaments blood clots (e.g. collagen and keratin)  Contractile proteins in movement: muscle, microtubules (cytoskelton, mitotic spindle, cilia, flagella) Protein
  12. 12. Globular proteins  most proteins which move around (e.g. albumen, casein in milk)  Proteins with binding sites: enzymes, haemoglobin, immunoglobulins, membrane receptor sites Protein
  13. 13. Proteins classified by function  CATALYTIC: enzymes  STORAGE: ovalbumen (in eggs), casein (in milk), zein (in maize)  TRANSPORT: haemoglobin  COMMUNICATION: hormones (eg insulin) and neurotransmitters  CONTRACTILE: actin, myosin, dynein (in microtubules)  PROTECTIVE: Immunoglobulin, fibrinogen, blood clotting factors  TOXINS: snake venom  STRUCTURAL: cell membrane proteins, keratin (hair), collagen Protein
  14. 14.  Conjugated Proteins Yield amino acids and nonprotein products upon hydrolysis  Glyco- or mucoproteins : Proteins plus carbohydrates; e.g. mucin of saliva  Lipoproteins : Proteins plus a lipid; e.g. liporutellin of egg yolk  Chromoproteins : Proteins plus a pigmented prosthetic group e.g. hemoglobin, myoglobin  Metalloproteins : Proteins plus a metal element such as iron, magnesium, copper, or zinc; e.g. ferritin (Fe), tyrosine oxidase (Cu), alcohol dehydrogenase (Zn).  Nucleoproteins : Proteins plus nucleic acid; e.g. nucleohistone  Phosphoproteins : Phosphoric acid is the prosthetic group; e.g. Casein (milk) Protein
  15. 15.  Derived Proteins: Derivatives of proteins due to action of heat, enzymes, or chemical reagents.  Primary Derived I. Coagulated Proteins II. Proteans III. Metaproteins  Secondary Derived Protein
  16. 16.  Complete protein: A complete protein contains essential amino acids to maintain body tissues and to promote a normal rate of growth and is referred as having a high biological value. Examples are egg, milk and meat (including poultry and fish) proteins wheat germ and dried yeast have a biological value approaching that of animal source.  Partially complete proteins: They will maintain life, but lack sufficient amounts of some of the essential amino acids necessary for growth. Adults under no physiological stress can maintain satisfactory nutrition for indefinite period when consuming sufficient amount of protein from certain cereals or legumes- gladden of wheat.  Totally incomplete proteins: These type of proteins are incapable of replacing or building new tissues and hence cannot support life and promote growth. Zein in corn and gelatin are examples of this type. Nutritional classification of Proteins Protein