Enzymes

- enzymes have 3D shapes.

- the part of the enzyme into which the substrate fits is called the active site.

- each active site is shaped specifically for the enzyme - substrate complex is formed. the substrate then undergoes a reaction.

- the product(s) formed are released from the active site while the enzye molecule is left unchanged and can catalyse the reaction.

- the enzyme is the lock while the substrate is the key.

- only a minute amount of enzymes are required to catalyse the reaction.

- enzyme reaction is specific.

- since the active site must fit the substrate perfectly, therefore only one enzyme can only catalyse one type of reaction.

- as the temperature increases, particles move faster, there is a higher chance of substrate and enzyme molecules bumping into each other, therefore the rate of reaction increases.

- enzymes work over a small range of temperatures.

- the rate of enzyme reaction increases as temperature increases - but only to a certain point.

- the temperature of which an enzyme works best is called the optimum temperature.

- beyond the optimum temperature, the rate of reaction catalysed by the enzyme decreases.

- very high temperatures alters the surface configuration of the enzyme molecule.

- when the active site changes shape, the enzyme can no longer bind with the substrate. the enzyme is then said to be denatured.

Effect of pH

- every enzyme functions best at its optimum pH.

- if the pH deviates too much from the optimum pH (either too acidic or alkaline), the presence of excess H+ or OH- ions can alter the surface configuration.

- when the active site changes shape, the enzyme cannot bind with the substrate.

Co-enzymes and Enzyme Inhibits

- co-enzymes are compounds that bind the enzyme molecule before the reaction. (example : Vitamin B complex)

- enzyme inhibitors are poisons that inhibit the enzyme from carrying out its function.

- one type of inhibitor binds with the active site and destroys the enzyme.

- another type of inhibitor compresses the enzyme molecule and changes the active site. (example : cyanide compounds)

Substrate Concentration

- under optimum conditions, as the substrate increases, the rate of reaction increases, therefore the substrate is the limiting factor.

- as the increasing substrates have no effect on the rate of reaction anymore, therefore other fators like the temperature or the amount of enzymes may be limiting factors.

Industrial Uses of enzymes

~ Biological Detergents
- they remove stains, especially coloured ones from animal or plant sources like blood and egg.

~ Food Industry
- Pectinase -> breaks down pectin which holds plant cells together, thus making it easier to squeeze out / extraction of fruit juice, and also makes the juice clear.
- Protease in baby food - partially digests proteins to polypeptides, thus helping the baby to digest and absorb the food faster.
- Isomerase - changes glucose to fructose, a much sweeter sugar.
- Amylase - converts starch into sugars (glucose).

~ Medical Industry
- Biosensors make use of enzymes to measure the blood glucose level. the gel used in the sensor contains oxidase. when the gel comes into contact with glucose, oxygen is used up in the reaction catalysed by the oxidase. the change in the oxygen level causes a current to flow which is detected by the sensor. the current is DF for DF amount of oxygen being used up, so the sensor measures the amount of glucose that is present.

~Enzymes and Germination of seeds
-the seed absorbs water and the seed swells.
- the testa becomes permeable to oxygen and carbon dioxide.
- when water enters the seed, the water will dissolve the inhibitory substances that prevents germination.
- the enzymes become active with the absorption of water.
- cotyledons produce enzymes to digest the stored food so that the growing embryo can use it.
- in endospermic seeds (example : maize grain), the enzymes flow into the endosperm to digest the food stored there.
- in non-endospermic seeds (example : sword bean seed), digestion of the stored food occurs within the cotyledons.
- in either case, the stored foods are digested and the end-product of digestion are transported to the growing points of the embryo, namely the plummule and radicle.

Enzymes that catalyse hydrolytic reactions are known as hydrolases.