Enzymes (II)

  • Created by: An Di
  • Created on: 23-09-19 12:07

Factors that affect enzyme activity...


+Substrate Concentration

+Enzyme Concentration


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Enzymes controlled by...

+Regulatory Molecule




+Feedback Inhibitors

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Activators & Inhibitors

+Molecules that increase - Activators
+Molecules that decrease - Inhibitors

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Enzyme Inhibition

+Cells don't want all the enzymes to be working.

+Needs and conditions vary from cell.

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Allosteric Regulation

+Any form of regulation where the regularly molecule.

+An activator or inhibitor binds to the enzyme at some other region other than the active site.

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Competitive & Non-Competitive Enzyme Inhibitor

Competitive Enzyme Inhibitor

+It decreases the reaction rate when there isn't much substrate but can be out-competed by lots of substrates.

+In this case, there will be more substrate that inhibitor in the active site.

Non-Competitive Enzyme Inhibitor

+In this case, the enzyme-catalysed reaction will never reach its normal reaction maximum reaction even with a lot of substrates.

+This is because the active site has changed shape and now the substrate can't bind.

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+Non-protein helper molecules. Attached temporarily to the enzyme through ionic or hydrogen bonds, or permanently through stronger covalent bonds.

+Common co-factors - inorganic ions such as iron (Fe2+) and magnesium (Mg2+).

+DNA polymerase requires magnesium ions to function fully.

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+Subset of co-factors that are organic. The most common source of co-enzymes are dietary vitamins.

+Some vitamins are precursors and others act directly as co-enzymes.

+E.g. Vitamin C is a co-enzyme for several enzymes that take part in the building of the protein collagen, a key part of connective tissue.

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Prosthetic Groups

+Co-factors that instead of being temporarily bound to the enzyme, are tightly bound to the enzyme and form a permanent feature.

+E.g. Zinc form an important part of carbonic anhydrase - an enzyme that is required for the metabolism of carbon dioxide.

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Enzyme Compartmentalisation

+Enzymes often compartmentalised - stored in a specific part of the cell where they do their jobs - in a particular organelle.

+Compartmentalisation - enzymes needed for a specific process can be kept in the places where they act, ensuring that they can find the substrate readily, don't damage the cell and have the right micro-environment to work well.

+E.g. Digestive enzymes of the lysosome work best at a pH around 5.0, found in lysosome but not cytoplasm. Lysosomes digest waste products and remove them from cytoplasm.

+Enzymes are kept in the lysosome means that even if this organelle is damaged the enzymes are not going to work.

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Feedback Inhibition

+In this case, end product of a metabolic pathway acts on the key enzyme regulating into the pathway, stopping more of the end product from being produced.

+Allows for the correct amount of the product to be formed, when there is too much of the product being made it will block the enzyme, preventing excess of the product being in the cell.

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+Adenosine Triphosphate

+An allosteric inhibitor of some enzymes involved in cellular respiration. When there is lots of ATP, this prevents more ATP from being made.

+Because ATP is unstable, if too much is made, much of it might go to waste, breaking it back down into ADP and Pi. 

+ADP (adenosine diphosphate) is a positive regulator.

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