2 1 1 Identify The Role Of Enzymes In Metabolism Describe Th

Chemical Composition
Enzymes are large globular protein molecules – meaning they are made of large chains of amino acids, which have been folded into a specific shape; their effective functioning is dependent on their shape. A substrate is the molecule on which an enzyme acts. The enzyme and substrate fit perfectly together, with the smaller substrate specifically aligning itself on the surface of the larger enzyme molecule – this location is known as the active site. (lock and key model)

Enzymes can also have a non-protein group (e.g. vitamin (riboflavin = B2) or metal ion (zinc, copper)), this assists in the formation of active sites and is known as a cofactor. A cofactor can be easily separated from the protein of the enzyme; however its presence is essential for the enzymes function. Example – some poisons exert their toxic effect by disabling cofactors – hence inhibiting enzyme function

Role of Enzymes in metabolism

Acceleration of Chemical Reactions
Enzymes are able to speed up or slow down reactions, without a change in temperature. This is vital in cells as heat damages living tissue. In order for a chemical reaction to occur, an activation energy level must be reached – the role of the enzyme is to reduce the activation energy, by providing an alternate reaction pathway. This allows the reaction to proceed faster, without a change in temperature.

Lowering of Activation Energy
In order to reach the activation energy of chemical reactions, heat must be provided. This is not possible in living tissue, as heat will damage the tissue. The role of the enzyme is to reduce the activation energy, by bringing specific molecules together, rather than relying on random collisions)

Action on specific Substrates
Enzymes are substrate specific, meaning only one particular substrate molecule can work with one particular enzyme. This is due to the reciprocally shaped active site. Since the enzyme is never chemically alter by a reaction, it can be reused in subsequent reactions – enzyme controlled reactions are always reversible.

Characteristics of Enzymes

Temperature – sensitive
Enzymes within cells function best at the body temperature of the cell. Enzymes function normally up to a temperature of around 40c; they decrease beyond that, enzyme function stops all together at around 60c. This is due to the excessive heat, which breaks the hydrogen bonds in the enzyme – which alters its shape and structure – this is known as denaturing. Excessive cold also changes the enzyme shape and structure.

pH sensitive
Individual enzymes function best within a specific narrow pH range. Levels of acidity or alkalinity have a similar effect as excessive temperature – alters the shape and structure, which reduces the enzymes efficiency. Within most cells, enzymes function at neutral, or near neutral levels. However enzymes in the digestive tract function most efficiently in an acidic or alkaline medium. Example, pepsin and rennin (break down of proteins) – function best in a strong acid. Amylase functions best in a weak alkaline solution, as it breaks down starches in the mouth – the action of amylase breaking down starches stops once it reaches the stomach, due to the low pH of gastric juices.

Substrate specific
Enzyme molecules act only on one type of substrate; this is due to the “lock and key” fit of the active site and the substrate. Examples are – amylase acts on starch, changing it to glucose, rennin acts on caseinogens (protein in milk) making it curdle, and catalase converts hydrogen peroxide into water and oxygen gas.