Objectives Students should know : That enzymes act as catalysts lowering activation energy through the formation of enzymesubstrate complexes. The lock and key and induced fit models of enzyme action. Enzyme properties The properties of enzymes relating to their tertiary structure. Description and explanation of the effects of temperature, competitive and non-competitive inhibitors, pH and substrate concentration. Candidates should be able to use the lock and key model to explain the properties of enzymes. They should also recognise its limitations and be able to explain why the induced fit model provides a better explanation of specific enzyme properties

Enzymes are Biological catalysts Made of protein. Enzymes control chemical reactions that take place in the cytoplasm. Not used up during the reaction. Are specific. Require optimum conditions at which they work best

The minimum amount of energy needed to start the reaction, leading to the formation of a high energy intermediate = The Activation energy

Energy Progress of reaction Substrates Products High energy intermediate Activation energy Enzymes reduce the height of the energy barrier

Lock and Key enzyme + substrateenzyme-substrate complex enzyme + product

Active site The active site involves a small number of key residues that actually bind the substrates The rest of the protein structure is needed to maintain these residues in position

Enzymes can break substances down: animation

Example: starch digestion Starch Maltose

Or build larger molecules: Active site es

Induced Fit The enzyme moulds itself around the substrate molecule

Enzyme activity How fast an enzyme is working Rate of Reaction Rate of Reaction = Amount of substrate changed (or amount product formed) in a given period of time.

Rate of Reaction Enzyme activity Variable you are looking at

Enzyme activity Variables Temperature pH Substrate Concentration

Rate of Reaction Temperature o C - denatures o C Increase in Activity <5 o C - inactive

Effect of heat on enzyme activty If you heat the protein above its optimal temperature bonds break meaning the protein loses it secondary and tertiary structure

Effect of heat on enzyme activty Denaturing the protein ACTIVE SITE CHANGES SHAPE SO SUBSTRATE NO LONGER FITS Even if temperature lowered – enzyme can’t regain its correct shape

Rate of Reaction pH Narrow pH optima Disrupt Ionic bonds - Structure Effect charged residues at active site

Rate of Reaction Substrate Concentration

Rate of Reaction Substrate Concentration Active sites full- maximum turnover

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Digestive enzymes allow hydrolysis reactions to take place rapidly in the conditions found in the gut. Starch is broken down by amylases to glucose Proteins are broken down by proteases into amino acids Fats are broken down into fatty acids and glycerol

Why can humans digest starch but not cellulose?

Lactose intolerance At birth babies make lactase to digest milk sugar Some people stop making this enzyme when they get older They become Lactose intolerant

Problems If they eat milk products the lactose is not broken down The sugar stays in the gut. Water stays in the gut due to the sugar The person develops diarrhoea Bacteria digest the lactose, producing gas and causing pain Affected individuals must avoid lactose products

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