ENZYMES

ENZYMES

BIOLOGICAL CATALYSTS
1. Enzymes speed up chemical reactions in the body, acting as a biological catalyst. They catalyse METABOLIC REACTIONS in the body, such as digestion and respiration.
2. Enzyme reactions can be INTRACELLULAR, within cells. Or EXTRACELLULAR, outside cells, like inside the blood or digestive system.
3. Enzymes are globular proteins which have an active site, which has a specific shape. The active site is the part of the enzyme where the SUBSTRATE molecules (The substrate that the enzyme interacts with) bind to. Enzymes are HIGHLY SPECIFIC due to their 3D structure.
ACTIVATION ENERGY
1. In a chemical reaction a certain amount of ENERGY is needed to be supplied to the chemicals before the reaction can start, this is called the ACTIVATION ENERGY. It is often provided as heat. Enzymes (Catalysts in general also) lower the amount of activation energy required, meaning reactions not only happen at a lower temperature but also increases the rate of reactions.
2. When a substrate fits into the enzymes ACTIVE SITE, it forms a ENZYME-SUBSTRATE COMPLEX. This is what lowers the activation energy. Two reasons why:
  1. 1) If the two substrate molecules need to be JOINED together then the enzyme's active sit will hold them close together so reducing any repulsion between the molecules, allowing them to bond more easily.
  2. 2) If the enzymes is catalysing a BREAKDOWN reaction then fiiting the substrate into the active site allows the enzyme to put a strain on the bonds, so the substrate molecules break up more easily.
MODELS OF FIT
1. The LOCK AND KEY MODEL, is the idea that the enzymes only work with specific substrates which will fit into their active site. Early scientists came up with the idea of the lock and key model, where the substrate fits into the active site in the same way that key fits into a lock. However this was soon dismissed as the enzyme and substrate did not have to exactly fit into eachother. The enzyme substrate complex could change shape slightly.
2. The INDUCED FIT MODEL explains why enzymes are so specific and only form a bond to one specific substrate. The substrate doesn't only have to be the right shape, it also has to change the active site's shape in the correct way.
ENZYME SPECIFICITY
1. Due to their 3D structure enzymes are very specific and they usually only catalyse one reaction, for example maltase only breaks down maltose. This is because only one substrate will fit in the active site. The active site itself is determined by the enzymes 3D structure, which in turn is determind by its own primary structure.
2. Each different enzyme has a different 3D structure so a different active site shape. If the substrate does not fit into the active site then the reaction cannot be catalysed. Also if the 3D Structure is altered in any way, as will be the active site, this would mean that the substrate would no longer fit, so the enzyme will be unable to carry out its function.
ENZYME CONCENTRATION
1. The more enzyme molecules that there are in a solution then the more likely a substrate molecule is to collide with one and form and enzyme substrate complex. So increasing the rate of reaction. However if the amount of substrate is limited there comes a point where there is more than enough enzymes and adding more would have no further effect.
2. One possible question is how to inestigate the effect of enzyme concentration on the initial rate of a reaction. This would be measured by showing HYDROGEN PEROXIDE being broken down into water and oxygen by the enzyme CATALYSE.

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