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Enzymes protein molecules that act as biological catalysts. A chemical reaction only occurs if there is sufficient energy to begin the reaction. In the absence of enzymes, this energy requirement is high and is known as activation energy
Enzyme Structure Most enzymes are globular proteins that have a tertiary structure (some have a quaternary structure)
Active site The active site is created by the tertiary folding of the protein. The active site is the site on the surface on the enzyme that binds to the substrate molecule
Substrate compound that is acted on by an enzyme. Enzymes and active site are highly specific in their action- each enzyme acts on a particular substrate. The shape of the active site fits with part of the substrate molecule to form enzyme-substrate complex.
The lock and key model complementary shapes of the active site and the specific substrate as fitting together like a lock and key. If the ‘key’ (the substrate), does not fit into the ‘lock’ (the active site), then no reaction occurs.
The induced- fit model when a substrate binds to the active site of an enzyme, a change in shape (or conformational change) of the active site occurs. Active sites are flexible and capable of changing shape in order to conform to the shape of the substrate
Enzyme regulation of biochemical pathways Many chemical processes occur as a sequence of reactions, in which each reaction is catalysed by a specific enzyme and the product of one reaction becomes the substrate in the next reaction. Such sequences of reactions form biochemical pathways
Catabolic reactions are reactions in which substrates are broken down and energy is released. Catabolic reactions are exergonic because they release energy.
Anabolic reactions are reactions that require an input of energy in order to produce larger molecules from smaller substrates. Anabolic reactions are endergonic because they require energy. The energy is required to form bonds between molecules.
Factors affecting enzyme regulation All enzymes have specific conditions in which they perform at their best. Temperature, pH and the concentration of the substrate and enzyme all affect the rate of enzymatic reactions.
Temperature - high temps rate of reactions will increase as the temp increases as the warmer particles become during a reaction, the more rapidly they move, which makes successful collisions between them more likely to occur. However enzymes can be denatured at high temperatures
Temperature - low temps If enzymes are cooled below their optimum temperature, the rate of reaction will slow down, because particles will move slower, making collisions less likely, and because the bonds are not as flexible at lower temps and conformational changes do not occur
pH If enzymes are taken too far above or below their optimum pH, then the tertiary structure is affected (the enzyme may become denatured) and the substrate may not be able to bind, causing the rate of reaction to decline.
Enzyme concentration If the enzyme concentration is high compared to that of the substrate, the reaction will occur quicker as more enzyme molecules available, the more active sites there will be for the substrate to bind to.
Substrate concentration more substrate initially increases the rate of reaction if not all of the active sites of the enzyme present are occupied (the saturation point). The addition of substrates (reactants) increases the amount of product produced.
Irreversible inhibition bonds formed between the inhibitor and enzyme are strong (i.e. covalent bonds), so the binding is irreversible. This means the inhibitor blocks the enzyme’s active site permanently, so the enzyme will no longer be able to take part in reactions
Compounds that are irreversible inhibitors termed poisons. Cyanide is an irreversible inhibitor of a key enzyme in the electron transport chain. Inhibition of this enzyme stops the production of ATP by aerobic respiration, resulting in death.
Reversible inhibition part 1 bonds formed between the inhibitor and enzyme are weak so they are easily broken and the inhibition reversed. The inhibitor can move in and out of the active site, reducing the activity of the enzyme as its active site will not be available
Reversible inhibition part 2 because the binding is reversible, the reduction in enzyme activity can be partially overcome by increasing the concentration of substrate, which provides a greater chance for a substrate, rather than an inhibitor, to bind to the enzyme.
Competitive inhibition shape of the inhibitor is similar to the shape of the substrate that normally binds to the active sites of a particular enzyme so such inhibitors are able to bind to the active site of the enzyme, and block the substrate from binding to the site.
Non-competitive inhibition inhibitor binds to a site other than the active site (an allosteric site) changing the shape of the enzymes active site such that the substrate cannot bind, or it blocks the changes in shape needed for the reaction to progress once the substrate is bound.
Feedback inhibition occurs when a product produced late in a biochemical pathway acts as the inhibitor of an enzyme acting earlier in the pathway, stopping the action of the enzyme. Regulation of this type means that products will not continue to be produced.
Cofactors components are non-protein compounds that bind to the enzyme and are necessary for the functioning of that enzyme and enable them to catalyse a reaction. Cofactors can be inorganic ions or organic molecules
Coenzymes Organic cofactors. For certain enzymes, a specific coenzyme is required to catalyse reactions. Often the coenzyme is structurally altered during the reaction, but afterwards reverts to its original form, which allows it to be reused.
Types of Coenzymes vitamins, ATP, nicotinamide adenine dinucleotide (NAD), flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide phosphate (NADP).
Loaded and unloaded coenzymes unloaded form of a coenzyme is free to accept a proton, electron or a chemical group, and once it has accepted it, it is considered to be loaded. The cycling between loaded and unloaded forms is referred to as the cycling of a coenzyme.
Created by: emmawalton05
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