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Enzymes

Cell and Molecular Biology

QuestionAnswer
Enzyme Globular proteins which catalyse metabolic reactions. Biological catalysts which alter the rate of a reaction without undergoing permanent change. They can be used repeatedly and are effective in small amounts.
Metabolism The sum total of all the chemical reactions in a cell.
Anabolism Reactions which involve the synthesis of molecules and usually require energy.
Catabolism Reactions which involve the breakdown of molecules and usually release energy.
Describe the lock and key hypothesis. Each substrate (key) fits exactly into the active site (lock) of the specific enzyme.
Describe the induced fit hypothesis. The enzyme's active site is flexible and can change shape slightly to better fit a particular substrate instead of being a rigid shape.
What are two most important conditions which must be met for an enzyme to work ? 1) Enzyme must have physical contact with substrate 2) Enzyme must have an active site which fits the substrate
What is the effect of pH on enzyme action? Enzymes work best at their optimal pH. This varies based on the particular enzyme. Extremes in pH can denature enzymes. Changes in pH can affect the hydrogen and ionic bonds of enzyme active sites resulting in changes in shape of the active site.
What is the effect of temperature on enzyme action? 1) Increase in temperature increases kinetic energy of molecules leading to more collisions of enzyme and substrate - rate of reaction is increased 2) As temp increases beyond optimum point enzyme becomes denatured.
What is the effect of enzyme concentration on enzyme action? 1) Enzymes are not used up in a reaction; they work very efficiently in low concentrations. 2) As long as there is excess substrate, increasing enzyme concentration will increase the rate of reaction.
What is the effect of substrate concentration on enzyme action? 1) If concentration of enzyme is constant and substrate concentration is increased, rate of reaction increases. 2) If substrate concentration exceeds the available active sites, no further increase occurs until the active sites become free again.
What are the effects of competitive inhibitors on enzyme action? Inhibitor binds to the active site of the enzyme
What are the effects of non-competitive inhibitors on enzyme action? Inhibitor binds to the enzyme at a position other than the active site
Give three examples of enzyme inhibitors. succinic dehydrogenase, antabuse and organophosphates
What are the two main ways in which the rate of enzyme-catalyzed reactions can be measured? 1) Formation of products e.g. volume of oxygen produced when catalase acts on hydrogen peroxide 2) The disappearance of the substrate e.g. the reduction in concentration of starch when it is acted upon by amylase
What is meant by the denaturation of an enzyme? This is the change in the tertiary structure of an enzyme and shape of the active site such that the enzyme is no longer functional. This can be caused by extremes in temperature and pH. The first bonds to be broken in denaturation are hydrogen bonds.
What are enzyme inhibitors? Substances that directly or indirectly interfere with the functioning of the active site of an enzyme and so reduce its activity.
What are reversible inhibitors? Inhibitors which make temporary attachments to the active site. Two types: competitive and non-competitive
What are irreversible inhibitors? Inhibitors which bind permanently and usually destructively to enzymes.
Define catalyst. A substance which speeds up a chemical reaction but remains unchanged itself at the end.
Why are enzymes considered to be biological catalysts? They are protein molecules made by living cells which speed up chemical reactions but remain unchanged themselves.
Define substrate. The chemical (or chemicals) which an enzyme works on.
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