Protein Flashcards
Secondary structure of protein
- amino acids in polypeptide chain form bonds, giving shape e.g. Spiralled
- disulphides links: sulphur bonds with another sulphur in the same chain or in a neighbouring chain
- hydrogen bonds: hydrogen in one chain bonds with oxygen in another chain
Primary structure of protein
- sequence order of amino acids in a polypeptide chain
- amino acids join together by peptide bonds
- peptide bonds are formed between amino acids by a condensation reaction (loss of water)
Tertiary structure of protein
-pattern of folding in polypeptide chains
- spiral shape of secondary structure folded into fibrous or globular shapes
- fibrous: coiled or zig-zag shape, held together by strong cross links
Globular: irregular shape, held together by weak cross links
Elemental composition of protein
Carbon, hydrogen, oxygen, nitrogen, (phosphorus, sulphur)
Essential amino acid
Cannot be me made in the body and so must be obtained from food e.g lysine, methionine
Formation of peptide bond or link
The an OH from the COOH (carboxyl) group of one amino acid joins with a H from the NH2 (amino) group of another amino acid, with the loss of a molecule of water (condensation reaction)
Properties of protein
Denaturation, solubility, gel formation, Maillard reaction
Denaturation
The unfolding of a protein chain, resulting in an irreversible change in shape. Caused by heat, acids, enzymes, mechanical action
Solubility
Proteins are insoluble in water ( except albumin (egg white) in cold water and collagen (meat) in hot water).
Maillard reaction
Reaction between amino acids and carbohydrate (sugars) in dry heat, resulting in the browning of food e.g roast potatoes
Gel formation
Collagen heated in the presence if moist heat changes to gelatine, this can be dehydrated and sold in different forms e.g. Leaf, granules. When added to water and heated, it absorbs water forming a sol, which sets to a gel when cooled
High biological value protein
Contains all essential amino acids (complete protein)
Animal sources only (except soya beans)
Low biological value protein
Missing some essential amino acids (incomplete protein)
Plant sources only (except gelatine)
Supplementary value of protein
When low biological value protein foods are eaten together to give all of the essential amino acids, i.e the lack of an essential amino acid in one food is supplemented by another food e.g beans and toast (bread is high in methionine and low in lysine, beans are high in lysine and low in methionine, the combination complements each other and provides all of the essential amino acids.
Protein digestion in stomach
Rennin: casein >caesinogen
Pepsin: polypeptides > peptones
