Enzymes and their importance in plants and animals (25 marks) Enzymes are biological catalysts, which accelerate the speed of chemical reactions in the body without being used up or changed in the process. Animals and plants contain enzymes which help break down fats, carbohydrates and proteins into smaller molecules the cells can use to get energy and carry out the processes that allow the plant or animal to survive. Without enzymes, most physiological processes would not take place. Hundreds of different types of enzymes are present in plant and animal cells and each is very specific in its function.
Enzymes have an active site which has a complimentary base to a specific substrate, when these bind an enzyme-substrate complex is formed. There are two hypotheses for the formation of an enzyme-substrate complex; the lock and key hypothesis explains that only one substrate (they key) will fit into the active site (lock). The induced fit hypothesis is when the active site changes shape so that the enzyme moulds itself around the substrate.
Enzymes are proteins with a 3-D tertiary structure which can alter in shape if certain factors such as temperature, pH or substrate concentration change, and so the active site of the enzyme may no longer compliment the base of the substrate therefore fewer complexes can form and the reaction rate drops.
Coenzymes are organic compounds, often containing a vitamin molecule as part of their structure they are not permanently bound to the enzyme but are temporarily bound for the duration of the reaction and then move away once it is completed. One example of this is NAD, which transfers hydrogen away from one molecule to become reduced NADH+. This occurs in both aerobic and anaerobic respiration in animals, whilst also in the light dependant and light independent reactions in plants.
Temperature effects enzyme activity. Increasing the heat gives molecules more kinetic energy so they move around faster. This means...
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