2 Boardworks High School Science Enzyme Shape What are enzymes?Boardworks High School ScienceEnzyme ShapeEnzymes are biological catalysts – they speed up the chemical reactions that take place inside all cells, but without being used up in the process.There are many thousands of different types of enzyme, and each one catalyzes a different reaction.Enzymes occur naturally in all organisms, but they are increasingly being used in industrial processes.
3 Why do enzymes speed up reactions? Boardworks High School ScienceEnzyme ShapeEnzymes speed up reactions by lowering the activation energy (Ea) of a reaction. The activation energy is the energy needed to start a reaction.Different reactions have different activation energies.reaction (time)energy (kJ)Ea without enzymeEa with enzyme
4 Boardworks High School Science Enzyme Shape Why is shape important?Boardworks High School ScienceEnzyme ShapeThe shape of an enzyme is very important because it has a direct effect on how it catalyzes a reaction.Why do enzymes have different shapes?An enzyme’s shape is determined by the sequence of amino acids in its structure, and the bonds which form between the atoms of those molecules.Photo credit: University of Chicago Medical CenterStructure of human insulin-degrading enzyme (IDE) in complex with beta-amyloid, a peptide that forms harmful plaques in the brains of people with Alzheimer’s disease. The molecular surface of IDE is represented by light yellow. The N- and C-terminal domains of IDE are colored green and red, respectively. The beta-amyloid (blue) is entrapped inside the degradation chamber of the IDE molecule.Different types of enzymes have different shapes and functions because the order and type of amino acids in their structure is different.
5 Why are enzymes so specific? Boardworks High School ScienceEnzyme ShapeEnzymes are very specific about which reactions they catalyze. Only molecules with exactly the right shape will bind to the enzyme and react. These are the reactant, or substrate, molecules.The part of the enzyme to which the reactant binds is called the active site.This is a very specific shape and the most important part of the enzyme.Photo credit: JC Revy / Science Photo LibraryThe image shows a molecular computer graphics image of ribonuclease A, an enzyme involved in the destruction of messenger RNA (mRNA) in the cytoplasm of bacteria. On the left is its substrate, shifted away from the active site. Enzymes are biological catalysts; proteins that speed up the rates of reactions within cells. Each enzyme is specific for a particular reaction; interaction occurs (typically as a weak bond) between an active site on the enzyme and a reactant (or substrate) due to the arrangement of mutually attractive groups of atoms. This image displays the molecular surface (blue) & polypeptide chain: colors are used to represent the polarity of constituent amino acids.
6 What happens at the active site? Boardworks High School ScienceEnzyme ShapeIn the same way that a key fits into a lock, so a substrate is thought to fit into an enzyme’s active site. The enzyme is the lock, and the reactant is the key.++↔↔enzymereactant+enzyme-reactant complex↔products
7 Boardworks High School Science Enzyme Shape The lock and key modelBoardworks High School ScienceEnzyme ShapeTeacher notesThis four-stage animation demonstrates the principles of the ‘lock and key’ model. While showing the animation, the specific shape of the active site could be highlighted.Suitable prompts could include:What is special about the shape of the active site?Is the enzyme the ‘lock’ or the ‘key’?
8 Factors affecting enzymes Boardworks High School ScienceEnzyme ShapeThe rate of enzyme-catalyzed reactions depends on several factors. What are some of these?Factors that affect the rate of a reaction include:temperaturesubstrate concentrationpHsurface areaenzyme concentrationpressure.All enzymes work best at only one particular temperature and pH: this is called the optimum.Different enzymes have different optimum temperatures and pH values.
9 Factors affecting enzymes Boardworks High School ScienceEnzyme ShapeIf the temperature and pH changes sufficiently beyond an enzyme’s optimum, the shape of the enzyme irreversibly changes.This affects the shape of the active site and means that the enzyme will no longer work.When this happens the enzyme is denatured.denaturednormalheatpH
10 Enzymes and temperature Boardworks High School ScienceEnzyme ShapeTeacher notesThis five-stage animation could be used as a precursor to running the experiment in the lab, or as a summary exercise.
11 Boardworks High School Science Enzyme Shape Enzymes: true or false?Boardworks High School ScienceEnzyme ShapeTeacher notesThis true-or-false activity could be used as a review exercise on enzymes, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Colored cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.