biology4alevel600

These factors are: - Temperature - pH - Enzyme concentration - Substrate concentration   - Inhibitor concentration When an enzyme solution is added to a solution of its substrate , the molecules collide .  With time, the quantity of substrate ↓(changed into product) --> frequency of collisions ↓--> rate of reaction gradually ↓.  The reaction rate is fastest at the start of the reaction (substrate concentration is greatest). --> When comparing reaction rates of an enzyme in different circumstances, we should measure the initial rate of reaction. 1. Temperature As  t o  ↑, kinetic energy of reacting molecules ↑--> ↑ successful collision --> ↑ rate of reaction.  At optimal  t o enzyme's activity is maximal --> rate is maximal. Above this temperature, H bonds holding enzyme molecule in shape begin to break --> change tertiary structure of the enzyme (denaturation) --> active site is deformed --->  ↓ binding of substrate with enzyme -->  ↓  rate of reactio

Measurement of the rate of formation of the product or the rate of disappearance of the substrate . 1. Measurement of the rate of formation of  O 2  in the reaction: Mash up some biological material like potato tuber or celery stalks, mix them with water and filter the mixture to obtain a solution containing catalases .  Add the mixture to H 2 O 2   (hydrogen peroxide) in a test tube. Use small tubes --> not too much gas in the tube above the liquid.  Collect the gas in a gas syringe and recording the volume every minute until the reaction stops. Note - You can replace the gas syringe by an inverted measuring cylinder over water. 2. Measurement of the rate of disappearance of starch in the reaction: Add amylase solution to starch suspension in a test-tube.  Take samples of the reacting mixture at regular time intervals, and test for the presence of starch using iodine in KI solution.  When starch is present , iodine is dark blue. If the blue colour lightens, starch is breakin

Enzymes  are  globular  proteins that serve as biological catalysts.  They speed up or slow down metabolic reaction, but remain  unchanged. They may facilitate the breaking of an existing bond or the formation of a new  bond . Substrates = the molecules that bind to the enzyme Products   =  new substances formed. 1. Active sites Active site = area in enzyme's molecule where the substrate bind to enzyme --> enzyme-substrate complex.  The  R groups  of amino acids at the active site form  temporary bonds  with the substrate molecule. This pulls the substrate slightly out of shape, causing it to react and form  products . 2. Activation energy Activation energy  = energy the substrates need for changing themselves into products.  Heating  provides activation energy.  Enzymes  reduce  activation energy needed ---> reaction take place at  low  t o . They do this by  distort the shape  of the  substrate  when it binds at the enzyme's  active site . 3. Enzyme specificity Lock

3.1    Mode of action of enzymes 3.2    Factors that affect enzyme action Enzymes are essential for life to exist.  Their mode of action and the factors that  affect  their activity are explored in this section. Prior knowledge for this section is an understanding that  an enzyme is a biological catalyst that  increases the rate  of a reaction and remains unchanged when the reaction is complete. There are many  opportunities in this section for candidates to gain experience of carrying out practical investigations and analysing  and interpreting their results. Learning Outcomes Candidates should  be able to: 3.1    Mode of action of enzymes There are many  different enzymes, each  one specific to a particular reaction. This specificity  is the key to understanding the efficient functioning of cells and living organisms. a)   explain that  enzymes are globular proteins that  catalyse metabolic reactions b)   state that  enzymes function  inside cells (intracellular enzymes)  and outside

• Mode of action of enzymes • Factors that affect enzyme action Learning Outcomes Candidates should be able to: (a) explain that enzymes are globular proteins that catalyse metabolic reactions; (b) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity (the lock and key hypothesis and the induced fit hypothesis should be included); (c) [PA] follow the progress of an enzyme-catalysed reaction by measuring rates of formation of products (for example, using catalase) or rates of disappearance of substrate (for example, using amylase); (d) [PA] investigate and explain the effects of temperature, pH, enzyme concentration and substrate concentration on the rate of enzyme-catalysed reactions; (e) explain the effects of competitive and non-competitive inhibitors on the rate of enzyme activity; (f) use the knowledge gained in this section in new situations or to solve related problems.

From small to large 1. The larger biological molecules are made from smaller molecules. Polysaccharides are made from monosaccharides, proteins from amino acids, nucleic acids from nucleotides, lipids from fatty acids and glycerol. 2. Polysaccharides, proteins and nucleic acids are formed from repeating identical or similar subunits called monomers, and are therefore polymers. These build up into large molecules called macromolecules.  3. The smaller units are joined together by condensation reactions. Condensation involves removal of water. The reverse process, adding water, is called hydrolysis and is used to break the large molecules back down into smaller molecules. 4. The linkages that join monosaccharides are called glycosidic bonds. Th e linkages that join amino acids are called peptide bonds. Carbohydrates 5. Carbohydrates have the general formula Cx(H2O)y and comprise monosaccharides, disaccharides and polysaccharides. 6. Monosaccharides (e.g. glucose) and disaccharides (e.g.