Proteins

Proteins

1. Large molecules : high molecular weight (20,000 - 2mil)

2. Polymers: made up of smaller monomers

   • Amino acids!
     • 20 aa in a protein
       • 9 essential, 11 non-essential
         • Need essential from diet for body to make non-essentials
         • Withut essential aa, no protein formed.
     • P broken down into aa by Hydrolysis - eg saliva
       • Breaking of bonds by adding water
     • Not stored in body long - fresh supply of essental aa required daily.

3. Main componants of muscles and tissues, enzymes regulating metabolism and functions of body, structure of hormones & antibodies

4. NITROGEN (16%), CARBON, HYDROGEN, OXYGEN, sometimes SULFUR, PHOSPHORUS

5. To find how much protein in food, analyse how much prtotein nitrogen then x by 6.25

6. Adults don't require as much protein as childrren because they have stopped growing

7. High quality proteins: meat, milk, eggs

   • Because they contain all the essentail amino acids in the amounts needed to support protein tissue formation by the body.

8. Soy Beans: almost complete P

9. Properties: SOLUBILITY, WATER BINDING, STRUCTURE, DENATURATION, REDUCTION, HYDROLYSIS

   • SOLUBILITY
     • differences determined by amino acid sequence and composition
     • Soluble in water: histones (protein replication), ovalbumims (egg whites), lactalbumin (milk), albumins of blood.
     • Insoluble in water: keratin (hair/fingernails), collagen (bones, cartilage, connective tissue, epidermis)
     • Soluble in weak salt solutions: myosin (muscle tissue), lactoglobins (milk)
     • Soluble in acids: wheat glutenin, oryzenin (rice)
   • Water bindning
     • Through hydrogen bonding w/- muscle tissue of meats (ground products ie hot dogs, mince)
   • Structure
     • Primary: molecular weight, aa composition & seq along peptide chain.
     • Secondary: shape of coiled helix
     • Tertiary: folding of a chain over itself
     • quartenary: 2 or more polypeptide chains join
     • Changed through food processing
   • Denaturation: change in strcuture without breaking covalent bonds, or aa seq.
     • Loss of biological activity & changes in physical/functional proeprties (ie solubility)
     • Caused by heat, acids, solvents, concetrated salts, surface forces.
     • eg. 'Blanching; in freezing/canning fruits & veg, Cheeses/Yogurts, Hardening of egg whit in pan (heat denaturation), whipping of egg whites to foam (surface force), slow cooking meat.
     • Contributes to flavour & texture of food.
   • Reduction:
   • Hydrolysis: cleaving of peptide bonds by adding water molecule.
     • Complete: P broken down to aa cparts
       • Partial: protein hydrolsates,: flavours parts of soups, sauces, gravy. plant prteins hydrolysed by hydrochloric acid - neuatralised with alkali.