Enduring Understanding: Competition and cooperation are important aspects of biological systems

1. Enduring Understanding: Competition and cooperation are important aspects of biological systems Essential Knowledge 4.B.1: Interactions between molecules affect their structure and function

2. Life requires enzymes to speed up reactions • Enzymes belong to what class of macrmolecule? • proteins • How do enzymes work? • They lower the activation energy required to get a reactions started Biological Catalysts Reduce Energy Barrier

3. Life requires enzymes to speed up reactions • Why is the shape of an enzyme important? • Enzymes work with specific substrates • Enzymes must be able to bind to the substrate • The substrate must be complementary to the surface properties (shape and charge) of the active site • The substrate must fit into the enzyme’s active site The structure of an enzyme determines its function. Induced Fit of substrate + enzyme = enzyme substrate complex

4. Figure 8.15-3 Substrates enter active site. 1 Life requires enzymes to speed up reactions 2 Substrates are heldin active site by weakinteractions. Substrates Enzyme-substratecomplex Active site canlower EA and speedup a reaction. 3 6 Activesite isavailablefor two newsubstratemolecules. Enzyme Products arereleased. 5 Substrates areconverted toproducts. 4 Products

5. Life requires enzymes to speed up reactions • Enzyme Facts: • Enzymes are reusable • Enzymes are substrate specific • Enzymes lower the activation energy of a reaction • Enzymes change shape upon binding to the substrate – thus holding the substrate in such a way to favor breaking existing bonds and making new ones – Induced Fit

6. Interactions between molecules affect their structure and function • Many enzymes require nonprotein helpers in order to function • Cofactors and coenzymes interact with enzymes to cause structural changes that alter the activity rate of the enzyme • The enzyme may only become active when all the appropriate cofactors or coenzymes are present and bind to the appropriate sites on the enzyme

7. Interactions between molecules affect their structure and function • What is the difference between a cofactor and a coenzyme? • Cofactor – inorganic, such as the metal atoms zinc, iron and copper in ionic form • Coenzyme – organic molecule; many are vitamins

8. Interactions between molecules affect their structure and function • Other molecules and the environment in which the enzyme acts can enhance or inhibit enzyme activity. • Environmental factors that may alter enzyme shape (particularly the tertiary structure) thereby altering enzyme function • Temperature • pH • Salt concentration

9. Optimal temperature forenzyme of thermophilic(heat-tolerant)bacteria (77°C) Optimal temperature fortypical human enzyme (37°C) Rate of reaction 120 60 0 20 40 100 80 Temperature (°C) (a) Optimal temperature for two enzymes Optimal pH for pepsin(stomachenzyme) Optimal pH for trypsin(intestinalenzyme) Rate of reaction 0 3 5 7 8 9 10 1 2 4 6 pH (b) Optimal pH for two enzymes

10. Interactions between molecules affect their structure and function • Molecules can bind reversibly or irreversibly to an enzyme’s active site or an allosteric site – changing the activity of the enzyme • Regulation of enzyme activity helps control metabolism • Allosteric regulation – (allo refers to “other”) a regulatory molecule binds to the enzyme at a site other than the active site - can either speed up (activator) or slow down (inhibitor) the reaction • Cooperativity – a substrate molecule binding to one active site in a multi-subunit enzyme triggers a shape change in all the subunits – increasing the reaction

11. (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition Substrate Activesite Competitiveinhibitor Enzyme Noncompetitiveinhibitor

12. (b) Cooperativity: another type of allosteric activation (a) Allosteric activators and inhibitors Active site(one of four) Allosteric enzymewith four subunits Substrate Regulatorysite (oneof four) Activator Stabilized activeform Inactive form Stabilized active form Active form Oscillation Inhibitor Non-functionalactive site Inactive form Stabilized inactiveform

13. Interactions between molecules affect their structure and function • Feedback inhibition is a common mode of metabolic control. An end product of a metabolic pathway can bind to an enzyme at the start of the pathway – changing the shape of the enzyme thereby “inhibiting” the reaction from taking place

14. Initial substrate(threonine) Active siteavailable Threoninein active site Enzyme 1(threoninedeaminase) Isoleucineused up bycell Intermediate A Active site ofenzyme 1 isno longer ableto catalyze theconversionof threonine tointermediate A;pathway isswitched off. Feedbackinhibition Enzyme 2 Intermediate B Enzyme 3 Intermediate C Isoleucinebinds toallostericsite. Enzyme 4 Intermediate D Enzyme 5 End product(isoleucine)

15. Interactions between molecules affect their structure and function • The change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. • These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/or presence of a competitive inhibitor.

16. Catalase + 2H2O2 Catalase/H2O2 complex  Catalase + 2H2O + O2 • What could we measure? • Disappearance of H202 • Production of H2O and/or production of O2 • Heat given off