Please Take out the Following Pencil Science Journal Agendas Macromolecules Worksheet (Pass it forward if you have not done so already). Plan for the week

Science Question of the Day Explain why the chemical bonds in the body do not break down, spontaneously, releasing all of their energy.

5.3 Chemical Reactions Chemical reactions begin with reactants (substrates) which are converted to products Exergonic reactions Products contain less energy than the reactants Endergonic reactions Products contain more energy than the reactants

Fig. 5.4 Energy of Activation Extra energy required to destabilize chemical bonds and so initiate a chemical reaction

However, they cannot make an endergonic reaction exergonic Fig. 5.4 Catalysts lower the activation energy of a reaction, and thus increase its rate However, they cannot make an endergonic reaction exergonic

5.4 How Enzymes Work Enzymes are proteins that serve as catalysts They speed up chemical reactions within cells Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely Active site Site on enzyme surface where reactant fits Binding site Site on reactant where enzyme binds They give the reactants a nudge so that they can come over the activation energy. Pushing a boulder down a hill vs. digging the ground under the boulder.

Fig. 5.5 Enzyme shapes determines its activity Lysozyme Changes upon binding of the substrate The substrate is now bound more intimately Enzyme shifts shape and encloses the substrate like a glove on a hand.

Fig. 5.6 How enzymes work Enzymes catalyze reactions by either bringing the molecules close to each other so that they can link up or by pressing on specific bonds to make them break easier.

Fig. 5.7 The catalytic cycle of an enzyme 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site Glucose Fructose Products are released, and the enzyme is free to bind other substrates. 4 The substrate binds to the enzyme, forming an enzyme-substrate complex. 2 H2O The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. 3 This is how they function to break bonds.

5.5 Factors Affecting Enzyme Activity Enzyme activity is affected by any change in condition that alters the enzyme’s 3-D shape The structural bonds of enzymes are sensitive to changes in temperature and pH Therefore, a temperature or pH beyond the optimal range will cause the enzyme to denature

Enzyme Activity

Fig. 5.8 Enzymes are sensitive to their environment Digests proteins in the stomach Digests proteins in the intestine Each enzyme functions at a specific pH and Tempreture and if those are interrupted, the Enzyme, a protein, will denature.

5.6 How Cells Regulate Enzymes A cell can control the activity of an enzyme by altering its shape Allosteric enzymes have shapes that can be altered by the binding of signal molecules These molecules bind to the allosteric site Repressors bind and repress enzyme activity Activators bind and restore or increase enzyme activity

Fig. 5.9 How cells control enzymes

Enzyme inhibition occurs in two ways: Competitive inhibition - Inhibitor binds at the enzyme’s active site Noncompetitive inhibition - Inhibitor binds at the enzyme’s allosteric site Fig. 5.10

Enzymes Reviewed