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Enzymes What, how, why, what Prior Learning • From GCSE what can you remember about Enzymes • Hopefully you got • Biological catalysts, proteins, specific shape, active site, substrate, What are ENZYMES • Biological catalysts – so they speed up the reaction whilst not being used up themselves. • They are made of PROTEIN and are GLOBULAR (so are folded and have a 3d shape) • Folding is due to two things • Sequence – what Amino Acid is where • Bonding – there are four types, ionic, disulphide, hydrophobic/hydrophilic interactions, hydrogen bonds • Look at the white board! Enzyme Facts • There are two types of two types! • Simple GCSE types – Catabolic, anabolic enzymes one breaks and one breaks can you guess which is which? • Correct Anabolic makes catabolic makes…. • Now AS level types – • Intracellular (inside cells) so for example catalase (more about that next week) • Extracellular (outside cells) for example digestive enzymes like trypsin, pepsin or amylase. Why does they work? • First GCSE revision – what affects the rate of reaction? • Temperature • Concentration • Surface area • Catalyst • Does anyone know why catalysts work? • They lower activation energy! A Bit of Detail • So, so far we know the following • Biological catalysts, Protein, Specific shape, Lowers activation energy • But how they do what do they do? • Simple • If joining the enzyme holds the two bits (molecules) together to overcome any repulsion • If splitting it puts a strain on the bonds and they break easily (see hydrolysis reactions) Shape matters • Indeed it does – the enzyme and substrate have to match to start with. • So if the protein strand is not right then the shape isn’t right then the substrate won’t bind • Example – Fabrys disease – lipases are not made properly and they build up in the kidney heart and other organs. • All because the enzyme can’t do this Two models • First lock and key model – substrate fits like a hand in a glove – look at white board!! • Second model – like the first but a bit different • Induced fit – a bit like tight jeans! A little bit of movement is needed makes the enzyme substrate relationship even more specific! SO Quick Recap • So far we have covered the following: • Enzyme structure – 1, 2, 3, 4 • Enzyme action – lock and key and induced fit (more useful and accurate) • Types of enzymes (intra and extra) • And factors affecting their action conc of enzyme and substrate • What enzymes actually do! SO Factors affecting enzymes • First rate of reaction revision: • Temperature • Concentration • Surface area • Catalysts Factors affecting enzyme performance • Temperature • Concentration • pH • Enzyme structure Graphs and limiting factors • Temperature – increases rate due to increased collisions then after optimum the enzyme structure breaks down • pH – Either side of optimum pH the H+ and OH- ions interrupt the tertiary structure and this changes the active site • Concentration of enzyme and substrate – Both increase until a plateau is reached then the reaction is limited due to not enough substrate or the active sites being Occupied Denaturation and occupied sites • IMPORTANT • Enzyme structure breaking down leads to DENATURING, not breaking – it is a specific thing that needs to be explained specifically!!! • Additionally – when an enzyme controlled reaction hits a limiting factor that is the enzyme it is because the active sites are OCCUPIED not USED UP – think of it like seats on a bus IMPORTANT!!!! • Temperature – increasing it increases rate of reaction • Temperature coefficient or Q10 is a value for the reaction that shows how much the rate increases when you increase the temperature by 10oC • At temperatures before optimum if the Q10 is 2 then the rate doubles for 10oC increase • A value of 3 will triple the rate • Most enzymes are at 2 Calculate Tangent • Worksheet! • Practice Questions Cofactors and inhibition • These are two different things • One stops and one makes it work, can you figure out which is which?!?!?!? • Correct cofactors – help • Inhibitors – no help Cofactors • Two types • Inorganic – the help the substrate and enzyme bond but are not changed or used in any way • Example Cl- for amylase • Organic – They are called coenzymes and participate in the reaction and are changed by it (second substrate) they also recycle • Example Vitamins e.g. NAD is derived from vitamin B3 • When a cofactor is bound to the enzyme it is known as a prosthetic group e.g. Zn ions on carbonic anhydrase Inhibition Again two types Competitive and Non competitive On white boards draw what you think this means. Correct • Competitive – hit the active site • Non competitive hit somewhere else (allosteric site) • We then move into permanent (non reversible) and non permanent (reversible) • That is all to do with the bonding – if it is strong covalent bonds no removal, if ionic or H then they can be removed Try the questions on page 110 of text book Special inhibition • End product inhibition • E.g. phospofructokinase an enzyme used in production of ATP lots of ATP inhibit it’s production – makes sense really • Enzyme inhibition – inactive precursors e.g. pepsin/pensinogen Questions • Can you explain the structure of enzymes • Explain how enzymes work • Outline all the factors that can affect enzyme function • Describe what a cofactor is and how they influence enzyme action • Outline an example of when an enzyme is inhibited in the body