Y11 Biology Unit Notes End of Year Exam

Biology: enzyme structure and function, factors that affect reaction rate, activation energy

Metabolism

Web of all enzyme-catalyzed reactions in a cell or organism

Anabolism

Synthesis of complex molecules from simpler molecules. This includes formation of macromolecules from monomers by condensation reaction

Catabolism

Breakdown of complex molecules into simpler molecules. This includes breakdown of macromolecules into monomers by hydrolysis reaction

Condensation reaction

Chemical reactions in which reactants are joined together to form a product with water

Hydrolysis reaction

Chemical reactions in which reactants are separated using water to form product

Endothermic Reaction

A reaction that absorbs energy in the form of heat

Exothermic Reaction

A reaction that releases energy in the form of heat

Collision Theory

1. Reactants (including enzymes and substrates) collide

2. with the correct orientation (i.e., in the "right" place)

3. with enough energy (E ≥ Ea)

Kinetic Energy

All matter is made of particles, all particles are in constant motion, the motion is random but linear, collisions are elastic

Enzyme

An enzyme is a biological (protein) catalyst.
● A catalyst increases reaction rate but is not used up (it is recycled).
● An enzyme is biological which means that it is found in living things. It is a protein.

Enzyme Specificty

An enzyme binds to and reacts with specific substrates according to the lock-n-key model. This explains substrate-enzyme specificity. The enzyme is the lock. The active site is the keyhole where the reaction takes place in the enzyme. The substrate must fit the active site - the shape of the substrate is complementary to the shape of the active site. The substrate is the key that fits into the active site which is the keyhole. The substrate is the reactant.

Enzyme Catalaysis

An enzyme increases reaction rate but is not permanently changed in the reaction
● An enzyme reacts with a substrate through an alternate reaction pathway
● The activation energy of alternate reaction pathway is less than that of the reaction pathway
without the enzyme

Reaction Rate

Change in a quantity over time, in terms of reactants, it is the rate at which they disappear. This is a negative change. In terms of products, it is the rate at which they appear. This is a positive change.

Reaction Rate Equation

The equation is change in amount ÷ change in time. Amount may be volume (of a gas), mass, temperature (change is a consequence of the reaction), height, length and so forth.

Reaction Rate Graph

Average rate is the change in amount / time (the slope) Instantaneous rate is the slope of a tangent at a given point

Example Reactants Analysis

As the reaction progresses, the concentration of reactants decreases. This leads to lower frequency of collision with the correct orientation and sufficient energy. Thus, rate decreases as reactions progress - highest at the beginning and lowest at the end.

Factors affecting Reaction Rate

Temperature, concentration, surface area and PH