- Enzymes are biological catalysts that speed up the rate of metabolic reactions in the body without themselves being used up.
- Soluble in water as they have hydrophilic R groups on the outside of molecules.
- Globular proteins with a specific tertiary structure held together in a very precise shape.
- Intracellular enzymes work in cells. E.g. Hydrolases found in lysosomes ---> break down substances brought in a cell by phagocytosis by hydrolysis. ATPases found in mitochondria and are involved in the synthesis of ATP during aerobic respiration.
- Extracellular enzymes work outside cells. E.g. digestive enzyme amylase which breaks starch down into maltose in the alimentary canal.
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How Enzymes Work
- Enzymes have an active site (usually a cleft or depression in the shape).
- Active site has a very specific shape that can only fit one type of molecule to catalyse. This molecule is called a substrate.
- When enzyme and substrate are reacted together it is by chance that they collide with one another and the specific substrate fits into the active site complimentary to it's shape, like a key fitting into a lock (lock and key hypothesis). when the substrate binds to the active site of the enzyme temporary bonds are formed between the substrate and the R groups of some of the amino acids in the enzyme. This can then be called an enzyme-substrate complex.
- In most enzymes when a substrate enters the active site the entire shape of the enzyme changes to accomodate it and hold it in the right position for it to react (induced fit hypothesis)
- One way or another the shape of the active site and the substrate have to be a perfect match (enzyme is specific to one type of substrate (specificity)).
- Enzymes can catalyse reactions in which two substrates are put together to form one new molecule aswell E.g. in the linkage of amino acids to form a polypeptide on a ribosome. Interaction between the R groups of the enzyme and the atoms of the substrate can break, or encourage formation of, bonds in the substrate molecule.
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