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Protein
| Question | Answer |
|---|---|
| Primary Structure | This is the order of amino acids in the polypeptide chain • Amino acids are linked by peptide links • Amino acids join with the loss of water |
| Secondary structure | This is further linking of the amino acids on the chain • This gives it a more definite shape • There are cross links between amino acids. Two examples of cross links are * Disulfide links * Hydrogen bonds |
| Disulfide links | This occurs when 2 sulfurs join together • E.g. two cysteine amino acids link together • The links can bring two polypeptide chains together or can give a definite shape to one polypeptide chain • Insulin is a protein that has disulfide links |
| Hydrogen bonds | The hydrogen in one amino acid links with the oxygen from another amino acid • Collagen is an example of a protein with hydrogen bonds |
| Tertiary structure | This is the excessive folding of the secondary structure . The secondary structure is folded over and held firmly in place by links . It is generally 3 dimensional It forms either a globular or fibrous structure |
| Fibrous | Fibrous is straight, spiral or zigzag in shape They are insoluble in water . E.g. collagen in meat and elastin in meat |
| Globular | Globular is spherical in shape . They are soluble in water • E.g. myoglobin in meat and ovalbumin in egg white |
| Biological value of protein | A measure of the protein quality in a food It is displayed as a % . It is determined by the number of essential amino acids the protein contains, in proportion to the bodies need |
| Complementary value protein foods | Eating 2 LBV foods together to get all the essential amino acids. Eating these foods together gives all the essential amino acids |
| Example of complementary value protein foods | E.g. beans on toast • Wheat is low in lysine & high in methionine • Beans are high in lysine & low in methionine • Eating these foods together gives all the essential amino acids |
| Denaturation | A change in the nature of the protein • The protein chain unfolds, causing a change to the structure • It is often an irreversible process • Denaturation is caused by a) heat, b) chemicals: acid and c) agitation |
| Foam formation | When egg whites are whisked •Protein chains unravel • Air bubbles are formed • Protein chains entrap air, creating foam • Heat produced slightly coagulates & sets foam |
| Gel formation | Collagen when heated forms gelatine •Gelatine absorbs water when heated •Protein chains uncoil & water gets trapped •Forms gel on cooling •Forms a 3D network which traps water •eg in cheesecake & mousses |
| Maillard reaction | Amino acid + sugar + dry heat = brown colour • Non enzyme browning • Occurs when food is roasted, baked or grilled |
| Elasticity of gluten | Gluten enables bread to rise during cooking |
| Functions of structural proteins | Growth and repair of the body |
| Functions of physiologically active protein s | Production of hormones, enzymes and antibodies |
| Function of nutrient proteins | Heat and energy Source of essential amino acids |
| Deanimation | process of excess protein broken down in the liver. • Left over amino acids go to the liver • The NH2 group is broken off, changed to ammonia, then to urea and then excreted. • The COOH group is oxidised to provide heat and energy |
Created by:
Caoimhek
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