Biology OATs

1) they lower [the energy that must be overcome in order for a chemical reaction to occur (activiation energy)] of a reaction.

2) they increase the rate of the reaction [how fast the concentrations of the reactants and products change.

3) they don't affect the overall /\ G of the reaction.

4) they are selective by catalyzing one reaction or one specific class of reactions.

5) they can decompose a product that they just helped to synthesize (enzyme rxns are reversible).

1) they are organic catalysts

2) they are proteins

3) they are not changed or consumed in the course of reactions.

4) many are conjugated proteins [which contain a non-protein cofactor].

Cofactors are nonprotein molecules required by enzymes to be present in order to become active enzymes

• 1) Prosthetic group:
• --bound firmly in the conjugated protein with covalent bonds.
• --can only be removed by denaturing
• --most contain an atom of metal (such as Zn²⁺ or Fe²⁺)

• 2) Coenzyme:
• --loosely bound in the conjugated protein
• --can be easily seperated from conjugated protein
• --can be modified during the catalytic reaction
• --most cannot be synthesized by the body & are obtained by the diet.

Defined as the maximum amount of work obtainable from a reaction or the net exchange of energy between the system and its environment.

1) A catalyst is any substance which affects the rate of a chemical reaction without itself being changed.

2) An example is an Enzyme

all living systems must have continuous controlled chemical activity

the spatial structure of an enzyme's active site is exactly complementary to the spatial structure of its substrate. The two fit together like lock and key; this theory is largely discounted.

the active site of an enzyme has flexibility of shape. When the appropriate substrate comes in contact with the active site, the active site changes shape to fit the substrate.

1) Temperature

2) pH

3) Concentration of enzyme and substrate

As the temperature increases, the rate of the enzyme action increases, until an optimal temperature is reach (usually ~40^oC). Beyond optimal temp., heat alters teh shape of the active site and deactivates it, leading to rapid drop in rate.

When the concentration of the substrate and enzyme are low the reaction rate is low due to unoccupied active sites of enzymes. When increasing the substrate concentration the reaction rate will increase until all active sites are occupied.; Note: V = reaction velocity; [S] = substrate concentration

For each enzyme there is an Optimal pH above and below which an enzyme activity declines. Maximal activity of Human enzymes ~7.2 ; except pepsin which is 2 (highly acidic) and pancreatic enzymes at 8.5 (highly basic = alkaline conditions).

• 1) Hydrolysis: Digests large molecules into smaller components by the addition of water. In multicellular organisms digestion occurs outside the cells, in the gut. Other hydrolytic rxns occur within cells.
• =Examples:
• Lactose ^lactase> glucose + galactose

Lipids ^lipases> fatty acids + glycerol

2) Synthesis: these reactions use the same enzymes used in the hydrolysis rxns to build larger molecules, but the direction is reversed. They occur in different parts of the cell, such as the ribosomes for the synthesis of protein from amino acids.

• 1) Growth
• 2) Repair
• 3) Regulation
• 4) Protection
• 5) Production of food reserves (such as fat & glycogen)