Starter a Function of proteins Learning intention Learn

Starter

a) Function of proteins Learning intention Learn about the function of proteins in living things.

Uses of proteins

b) Amino Acids Learning intention Learn about the characteristic chemistry of amino acids, the building blocks of proteins.

Amino acids All proteins contain the elements C, O, H, N. They are condensation polymers, made by amino acids linking together. The body cannot make every type of amino acids that it needs. So our diet must contain essential amino acids. (about 10 of them). We synthesis the others. Amino Acids H R O H N C C R O H NH 2 CHCOOH Most proteins contain 20+ different amino acids H When R is Hydrogen, the amino acid is glycine (Gly) (aminoethanoic acid) When R is CH 3, the amino acid is alanine (Ala) (2 -aminopropanoic acid)

Amino acids

c) Amide links Learning intention Learn how proteins are formed by condensation reactions of amino acids to produce amide (peptide) links.

Protein Polymers Proteins are condensation polymers, made by amino acids linking together. An amine group of one molecule links to the carboxyl group of another molecule to form an amide link or peptide bond.

Protein Polymers H CH 3 H O N–C-C OH H H + glycine alanine CH 3 H H N–C-C O OH H alanine Tripeptide, ala-gly-ala H CH 3 O H H O H CH 3 O N–C– C - N–C–C- N–C-C OH H H Polypeptide chain can have 10000 amino acids amide (peptide) link + 2 H 2 O

d) Hydrolysis of protein Learning intention Learn how proteins are broken down to amino acids by the process of hydrolysis.

Essential Amino acids The body cannot make all the amino acids required for body proteins and is dependent on dietary protein for supply of certain amino acids known as essential amino acids

Protein hydrolysis Proteins are broken down during digestion. Digestion involves the hydrolysis of proteins to form amino acids Protein + 2 H 2 O Amino acids

Experiment 1. Place the test tube in a water bath and leave until the contents reach the same temperature as the water bath. 2. Use the 2 cm 3 syringe to measure out 1 cm 3 of lipase from the beaker in the water bath for the temperature you are investigating. 3. Add the lipase to the test tube and start the stopclock/ stopwatch. 4. Stir the contents of the test tube until the solution loses its pink colour.

Explanation • Phenolphthalein is an indicator that is pink in alkaline solutions of about p. H 10. When the p. H drops below p. H 8. 3 phenolphthalein goes colourless. Here, an alkaline solution of milk, lipase and phenolphthalein will change from pink to colourless as the fat in milk is broken down to form fatty acids (and glycerol) thus reducing the p. H to below 8. 3. The time taken for this reaction to occur is affected by temperature.

Changes in protein structure on heating • Within proteins, the long chain molecules may be twisted to form spirals, folded into sheets, or wound around to form other complex shapes. • The chains are held in these forms by intermolecular bonding between the side chains of the constituent amino acids. • When proteins are heated, during cooking, these intermolecular bonds are broken allowing the proteins to change shape (denature). These changes alter the texture of foods.

Enzyme Activity Enzymes catalyse chemical reactions in the body. Each enzyme has a unique shape held together by many weak bonds. Changes to p. H and temperature can denature the enzyme. This changes the enzymes shape stops it working properly. Narrow optimum range Enzyme activity Temp or p. H The bonds that hold most biological enzymes are broken around 60 o. C.