To be successful today NEW SEATING CHART!!! Last Day to pay for AP Exam TODAY!! Biomolecules Unit TEST WED 10/30 Clear off deskall you will need is a pencil Enzymes: The Biological Catalysts
Chapter 8.4 & 8.5 Learning Objectives Describe the properties of enzymes. Explain why the shape and charge of the substrate must be compatible with the active site of the enzyme. Explain how enzymes facilitate chemical reactions by lowering the activation energy. Explain how changes to the enzyme
structure affect its function. Explain how changes to the cellular environment affect enzyme activity. Energy of Activation The amount of energy needed for a reaction to occur is called the energy of
activation. The energy used to break the bonds in the reactants so they can be reformed as products. 4 Enzymes Lower Activation Energy
Enzymes are biological catalysts that increase the reaction rate of biochemical reactions by lowering the energy of activation. 5 Mechanism of Enzymes 6
Enzymes Work by Lowering the Energy of Activation Enzymes do NOT change Gibbs free energy or G. (the total amount of energy available to do work) 7 Enzyme Structure Substrate- These
are reactants that interact with the enzyme during a biochemical reaction. Active site- This is the part of the enzyme actually involved in the chemical reaction.
8 Characteristics of Enzymes Made of proteins (or RNA). They are very specific and only work with a certain set of reactants or substrates that fit on their active site.
Enzymes can be used over and over again Usually end in -ase 9 Lock & Key Model 10 Induced Fit Model
When an enzyme binds with the substrate, the substrate interacts with the enzyme causing it to change shape. This change in shape facilitates the chemical reaction to occur. This is called the induced fit. 11 12
Enzyme Example Ribonuclease Ribonuclease decomposes RNA, and the nucleotides can be recycled. The purple part is the enzyme; the green part is the substrate (RNA). 13
The Enzyme Sucrase Decomposing Sucrose 14 Factors that Affect Enzyme Rates Amount of substrate Number of enzymes
Temperature/ pH Inhibitors Allosteric Regulation Cooperativity 15 Initial Velocity The reaction rate of an enzymatic reaction is always fastest at the beginning of the reaction when there is
the greatest concentration of substrate. Why? 16 Initial Velocity At first, the amount of product formed increases, then the rate slows down as the concentration of substrate decreases.
If the amount of enzyme is kept constant and there is an increase in the amount of substrate, there will be an increase in the initial velocity until a saturation point is reached. 17
Effect of Increasing Substrate Concentration The initial velocities increase because there is more substrate to attach the enzyme, but eventually there is no increase in initial velocity because all of the enzymes have become saturated with substrate. 18 Effect of Increasing Temperature
At first, an increase in temperature will increase the reaction rate because of the kinetics of the reaction, but after a certain temperature is reached, the hydrogen bonds fall apart and the enzyme will denature. Notice that with thermophiles, natural selection has favored enzymes that can tolerate higher temperatures. 19 Effect of Varying pH
Most enzymes work best at a pH range of 6 to 8, but there are some exceptions, such as pepsin. If the environment changes much from the optimum pH, again hydrogen bonds are affected, denaturing the enzyme. 20 A
B D C 21 Effect of Competitive Inhibitors Inhibitors- are chemicals
that inhibit the action of an enzyme. A competitive inhibitor resembles the substrate enough that it can bind to the active site in place of the substrate. This will slow down the reaction rate as a certain percentage of the
enzyme will combine with the inhibitor. 22 Effect of Noncompetitive Inhibitors A noncompetitive inhibitor does not bind to the active site but to some other place on the enzyme
causing a conformational change This causes the active site to change shape so that substrate cannot bind. 23 Feedback Inhibition
Enzymes usually work in biochemical pathways in which there are a series of chemical reactions that occur in order to get from point A (reactants) to point B (products). It is not unusual for an end product to act as an inhibitor to shut down the pathway
when there is sufficient product present. 24 Effect of Allosteric Regulation Allosteric Regulation - regulation by changing the structure of a molecule Such enzymes have two or more polypeptide chains each with its own active site.
25 Effect of Allosteric Regulation This causes two conformations-one with a functional active site to bind an activator and the other with a nonfunctional active site to bind an inhibitor. The activator will stabilize the conformation with the functional active site and the inhibitor will stabilize the inactive form of the enzyme.
26 Effect of Cooperativity Occurs when there are two or more sub-units to an enzyme, each with its own active site. When one substrate binds with one active site, the enzyme changes
conformation so that the binding of other substrates are easier to achieve. 27 Learning Objectives Summaries
