Enzymes explain the induced fit model of enzyme action evaluate the strengths of the induced fit model against the lock and key theory apply knowledge of tertiary structure to explain enzyme specificity and the formation of enzyme-substrate complexes. Structure of Enzymes: All enzymes are tertiary globular proteins, where the protein chain is folded back on itself into a spherical or globular shape. Each
enzyme has its own sequence of amino acids and is held in its tertiary structure by hydrogen bonds, disulfide bridges and bonds. Thisionic complex 3D shape gives the enzyme many of its properties.
How Enzymes Work: Enzymes are biological catalysts - they speed up the rate of metabolic reactions, without being used up themselves. These reactions can be of two types: where larger molecules are broken down 1. Reactions into smaller molecules. 2. Reactions where small molecules are built up into larger, more complex, molecules. Enzymes react with another molecule called the SUBSTRATE. Each enzyme has its own special shape, with an area, the ACTIVE SITE, onto which the substrate molecules bind. This is known as the lock and key theory. You will
have seen this at GCSE. Models of enzyme action: lock-and-key 4 of 34 Boardworks Ltd 2008 How Enzymes Work: Modern interpretations of the lock and key theory suggest that in the presence of the substrate, the active site may change in order to fit the substrates shape. This is called the INDUCED FIT HYPOTHESIS.
Enzyme + Substrate Enzyme-Substrate complex Enzyme + Product Models of enzyme action: induced fit 6 of 34 Boardworks Ltd 2008 Properties of Enzymes: Enzymes are specific i.e. each enzyme will catalyse only one particular reaction, for example, sucrASE acts on the sugar, sucrOSE. Chemical reactions need energy areoff
very efficient and toEnzymes start them - this is called have a highENERGY. TURNOVER ACTIVATION NUMBER. This energy is needed to break This means that they can the
existing chemical bonds convert many molecules of inside molecules. substrate per unit time, for example, In the body, enzymes lower the catalase, which activation energy reactions
breaks down the of waste product and so reduce the input of energy hydrogen peroxide in the body, needed, allowingnumber reactions has a turnover of to
take place at lower several million pertemperatures. second! Why do enzymes increase the rate? 8 of 34 Boardworks Ltd 2008 Past Paper Question (5 min)
Mark Scheme Peer mark! a) 3 marks max Enzyme/active site has a (specific) tertiary structure Only glucose has the correct shape/ is complementary/ will fit To active site (Forming) enzyme-substrate complex DO NOT allow same shape! DO NOT allow active site is on the substrate Mark Scheme Peer mark! b) 2 marks max (Only detects glucose whereas) Benedicts detects (all) reducing sugars/ example(s)
Provides a reading/ is quantitative/ Benedicts only gives a colour/ doesnt measure concentration/ is qualitative/semiquantitative Is more sensitive/ detects low concentration Red colour/ colour of blood masks result Can monitor blood glucose conc. Continuously DO NOT credit quicker/ more accurate
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