OCR biology A - 2.2.4 enzymes

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enzyme jose its 30 shape and denature the substrate cannot fit into the enzyme causing a decrease in rate of reaction. ACTIVATION ENERGY In most chemical reactions, a certain amount of energy is needed to start the reaction. This is known as activation energy. Emymel reduce the amount of activation energy that is needed, which speeds up rate! of reaction. ANABOLIC L REACTIONS CATABOLIC S 3 Anabolic reactions are when. two substrate molecules need to be joined together. Enzymes hold the substrates close. together so they can bond easily. REACTIONS catabolic reactions. are when the substrate more coleneeds to be broken down. By filting into mue enzyme a strain isplaced on the subshater canding it to split. MECHANISMS OF ACTION BONDING Each level of structure is held together by. different kind of bonds. In tertiarys tv Ucture it is held to gether by the bonds listed below: B Ionic bonding-attractions between oppositely charged groups undirterent parts of the molecule. Disvifide bonds-occurs between two molecules of amino acid, cystine when a sulfur atom from each cystine hand to gether. HydrophilhHydrophobic interactions lydrophilic Romoups tend robe pushed to the outside of the structure because hydrophobic Agroups tend to clump to getner. Hydrogen bonds - These are weak bonds formed between slightly Poratively charged ny drogen atoms in R2 groups and slightly negatively charged ny drógen atoms in R'groups. ACTIVESITE Enzymes have an activerite where substrates bind to. These active sites have specific shape which is determined by the enzyme'ster tiary structure. Tertiary Structure includes the fulner folding and coiling of amino acias at TERTIARY more bonds form between. PROTEIN different parts of the polypeptide. STRUCTURE For Single polypeptide chains, tertiary structure forms their final 3D structure FACTORS AFFECTING RATE PH LEVELS All Enzymes have an optimum pH value with most human enzymes woru best at pH7, but there are exceptions such as pepsin (pt 2) PH A At low pls, the enzyme is surrounded by acidic solution (high proportion of HT ions). These ions. interrupt the ionic 6 mnding within the enzyme which causes the enzy me to lose its 30 shape anel denature The substrates no longer fit and there is a decrease in the rate of reaction! R BAS pt increases the ROR increases. At optimumpfl levels, the charge balance of solution does not interfere with bonding within the enzyme. Atthis point, the highest number of enzyme substrate complexes form and therefore where rate of reaction is at its nighest. At high pHs, the enzyme is surrounded by alla line solution Chigh proportion of oflions). OH ions interrupt the ionic bonding within the enzyme. Fewer enzyine substrate complexes form and late of reaction decreases B 2.2.4 ENZYMES SUBSTRATE CONCENTRATION AAt the start there are more enzymes than substrate. when the volume of substrates increases the number of enzyml substrate complexes and increases the rate of reaction Howeverat a certain point there is More substrate molecvies than free active sites. Enzyme concentration is now a limiting factor and the are of reaction levels out. INTRACELLULAR ENZYMES END PRODUCT INHIBITION NON-COMPETITIVE INHIBITORS g There are enzymer found inside the cell membrane they can either be present freely in the cytoplasm or they may be bound to some organelles such as ribosomer. They may also be present within organelles such as mitochondria, nucleus and others They are mostly prodvied. by ribosomes because they are protiens. An example is glycosis where glucose il broken down into pyruvic acid. ENZYME CONCENTRATION B EXTRACELLULAR ENZYMES Extracellular enzymes are found outside in extracellular fluid. They catalyse. chemical reactions taking place outside of the cells for example in the saliva, blood, stomach, etc. They are alsuprocessed runough the ribolmes Example of these enzymes include Pepsin, cipare and many more. INHIBITORS COFACTORS However at a certain point, most Substrate molecules have been briuen down leaving active sites empty. substrate availability is now a limiting factor. The ROR levels out. PH LEVELS The effect of pH levels on catalare activity. AAt the start there are more substrates than enzymes, when The effect of pt can be determined. the volume of enzyme by changing the pH level and is inceared, number measuring its effect on the rate of reaction. of enzymu substrate complexes are formed, increasing ROR control variables: Volume of catalase solution volume of pH buffer. volume of hydrogen peroxide remperature Independent variable: The level of pH Dependent variable: The time taken for each cample to break down PRACTICAL INVESTIGATIONS •The product inhibits the enzyme that prooduces it •Normally used as a control mechanism SV cu as in negative feedback. •Excess products are not made, and resources are not waited. Examples include ATP inhibition. of phosphofructo kingse COMPETITIVE INHIBITORS either V- The inhibitor is not a similar shape to the substrate. It also has a different site to attach to called anallosteric site. when it bonds to the allosteric site it changes the active Jite of the enzyme preventing me Substvale to bind with it; this is usually an irreversible inhibition. Examples of this include toxic substances such as organophosphates and proton pump inhibitors. This substrate can bind the degree ut inhibition will depend inhibitor also affects the v max. substrate concentration In this case the inhibitor hal a similars have to the substrate and canfit into the active site. This meant it comperes with the actual substrate to fit into the active site this slow down, the rate of reaction as less upon the relative concentrations of substrate, inhibitor and enzyme Examples include staring and aspirins. COENZYMES cofactors are inorganicions which help some enzymes function properly. They are normally temporarily bound to the enzyme Coenzymes are a type of cofactors. which are organic (contain carbon). They and help stabilise the structure of the entyme they wore by helping the enzyme and substrate bind together Examples could include now chloride ions (CI) are cofactors for amyldre. These cofactors are can either be permenantly bound, near or in the active site, or temporarily bind during the reaction. They are obtained through vitamins through diet. They link diff event enzyme- catalysed reactions in to a sequence. obtained through minerals through Examples include, nictonic acid which is used to produce the coenzymes in TEMPERATURE The effect of temperature on Milk hydrolosic: e effect of temperature can be determined by changing the temp and measuring its effect on the vate. of reaction. no inhibitor control variables: volume of milu cone and vol of crypsin solution Time all samples are left in water bath sinnipited. Independent variable: temperature Dependent variable: time taken for milk sampus to hydrolyse. O VMAY PROSTHETIC GROUPS Prosthetic groups are a type of cofactor that ispermenantly part of the enzymer structure, they help form the final 3D shape of the enzyme They can eitnerve inorganic or organic and are obtained through vitamins and minerals through diet. They can either bind at the enzymer active site or at an allosteric sire. An example of a prosethitic group could be carbonic anhydrare which is an enzyme in red blood cells, which catalyses the production of carbonic acid from water NAD and NADP which are coenzymes to carbon dioxide. These enzymes require 20¹1 ions which are a permenant part of required in many different metabolic. the enzymel active site. reactions. no inhibitor substrate conceneratio non-competitiv misitor. SUBSTRATE CONCENTRATION The effect of substrate concentration on catalase activity The effect of changing substrate concentration can be determined by increasing substrate concentration and measuring its effect on the rate of reaction. control variables: volume of cellery extract, volume of hydrogen peroxide solution, same size / typel width of paperdirus Independent variable: substrate concentration Depen de nt variable: Time taken for disk to float to the top of the hydrogen peroxide solution