1. Define the following and explain how each relates to the lactase chemical reaction. ➔ Enzyme ➔ Substrate ➔ Activesite ➔ Rateofreaction ➔ ActivationEnergy 2. What is the chemical reaction that lactase catalyzes? 3. Why would having the enzyme lactase as an adult be an evolutionary advantage? 4. Explain how the structure of an enzyme relates to how well the function catalyzes chemical reactions.

Answer / Explanation:

Question 1Enzyme

An enzyme is a biological catalyst that speeds up the rate of a chemical reaction. Enzymes are usually proteins. In the case of the lactase chemical reaction, lactase is the enzyme that breaks down lactose into two smaller sugars: glucose and galactose.

Substrate

The substrate is the molecule that the enzyme acts on (in chemistry is usually called the reactant). The substrate is usually converted into a product via the actions of an enzyme. In the case of the lactase chemical reaction, the substrate is lactose and the products are glucose and galactose.

Active site

The active site of an enzyme is the site of the enzyme in which catalysis takes place. I. e. it is the site where the enzyme brings the substrate in order to bring about the chemical change required to convert it into a product. In the lactase chemical reaction, the active site is present in the lactase enzyme, and is the site of the hydrolysis of the glycosidic bond.

Rate of reaction

The rate of the reaction is the speed at which a chemical reaction occurs. This could be under a second to hundreds of years. Enzymes reduce the rate of reaction without undergoing any chemical change themselves. In the case of the lactase chemical reaction, lactase reduces the rate of reaction of the hydrolysis of lactose

Activation Energy

The activation energy refers to the minimum energy required in order for a chemical reaction to begin. This is because a certain amount of energy is required to get molecules into a transition state, where they are capable of undergoing chemical reactions. This state is unstable and involves breaking bonds. Enzymes act by lowering the activation energy required to start a reaction. In the case of the lactase reaction, lactase lowers the energy required to convert lactose into glucose and galactase.

Question 2

The chemical reaction that lactase catalyses is called hydrolysis. A hydroysis reaction uses water to break down complex molecules. In this case, lactose (a disaccharide) is hydroylsed into glucose and galactose (two monosaccharides). This involves breaking a glycosidic bond, and the overall reaction is

C12H22O11 + H2O → C6H12O6 + C6H12O6 ( + heat) Question 3

Historically and in most mammals, lactase activity in humans is lost after weaning (when babies no longer need to digest their mother's milk for their primary nutrition). However, persistent lactase activity has developed relatively quickly over time in some human populations. This is thought to be a result of the domestication of animals, and the discovery that humans can use their milk as a food source.

Having lactase enzyme into adulthood means that you can breakdown milk products into sugars the body can use for energy. This is particularly useful during periods of famine or extreme poverty, when food supply is scarce. If some individuals can utilise milk as an efficient source of energy (because they can breakdown lactose) then they will be stronger and fitter. Therefore, it confers an evolutionary advantage.

Question 4

The structure of an enzyme is crucial in its ability to catalyse chemical reactions. This is related to the active site, where the reaction is catalysed. The active site has a specific shape and properties (i. e. specific amino acids) that allow it to bind to the substrate. The substrate molecule can bind to the active site, where it can be held in the correct orientation in order for the reaction to take place at an increased rate.