Enzymes 20/11/2018 Learning Outcomes You should be able to: Interpret energy level diagrams including identification of activation energy, and use them to explain how enzymes work. Explain the induced fit model of enzyme action. Assess the strengths of the induced fit model against the lock and key theory.

What is an enzyme? Enzymes are globular proteins that act biological catalysts. Catalysts alter the speed of a reaction without being permanently changed themselves. The complex tertiary structure of the enzyme (held into place by ionic, disulphide and hydrogen bonds) determines many of the physical properties of the enzyme.

What is needed for a reaction to happen? Sucrose + water  Glucose + fructose

Energy level diagram

ACTIVATION ENERGY Chemical reactions need energy to start them off - this is called ACTIVATION ENERGY. This energy is needed to break the existing chemical bonds inside molecules. In the body, enzymes lower the activation energy of reactions and so reduce the input of energy needed, allowing reactions to take place at lower temperatures.

Lock and key model of enzyme action The molecule that the enzyme has its action on is called the substrate. Each enzyme has its own special shape, with an area, the ACTIVE SITE, onto which the substrate molecules bind. The active site has a shape which fits the substrate perfectly (enzyme-substrate complex formed). Once the reaction has occurred, the products of the reaction move away from the active site of the enzyme

INDUCED FIT MODEL OF ENZYME ACTION 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 substrate’s shape.

Biosensors These devices are made up of a transducer and a biological element that may be an enzyme, an antibody or a nucleic acid. The ‘bioelement’ interacts with the sample being tested and the biological response is converted into an electrical signal by the transducer. 

Biosensors

Past Paper Question (5 mins)

Mark Scheme – Peer mark! a) 3 marks max Enzyme/active site has a (specific) tertiary structure ü Only glucose has the correct shape/ is complementary/ will fit ü To active site ü (Forming) enzyme-substrate complex ü DO NOT allow ‘same’ shape! û DO NOT allow active site is on the substrate û

Mark Scheme – Peer mark! b) 2 marks max (Only detects glucose whereas) Benedict’s detects (all) reducing sugars/ example(s) ü Provides a reading/ is quantitative/ Benedict’s only gives a colour/ doesn’t measure concentration/ is qualitative/semiquantitative ü Is more sensitive/ detects low concentration ü Red colour/ colour of blood masks result ü Can monitor blood glucose conc. Continuouslyü DO NOT credit ‘quicker’/ ‘more accurate’û