1. 7.6 Enzymes

2. Metabolic Pathways • Metabolic pathways are specific sequences of enzyme-catalyzed reactions that often occur in chains or cycles Glycolysis Calvin Cycle

3. Remember… Anabolism – the building of larger organic molecules (condensation reactions) Catabolism –the breakdown of organic molecules (hydrolysis reactions) All living things MUST • Grow • Reproduce • Respond to stimuli • Maintain Homeostasis • Nutrition • METABOLISM – sum of all chemical reactions inside the living organism Ex: respiration, photosynthesis, digestion

4. Review Slide

5. The Induced-Fit Model • The Induced-Fit Model is a more accurate portrayal of enzyme-substrate relationship • Substrate does not fit perfectly into enzyme until it binds to active site • Once it binds the active site shape chages slightly, which weakens the bonds within substrate • Weakened bonds lowers activation energy and allows reaction to happen faster/easier

6. Activation Energy Activation Energy is the energy necessary to break bonds and/or make new bonds Enzymes lower AE by weakening the bonds in the reactants and allow reaction to take place easier/faster

7. Competitive Inhibition • Competitive inhibition is when a molecule that is structurally similar to a substrate binds with the needed enzyme; the result is fewer reactions between the “true” substrate and enzyme; affects can be reduced by adding more substrate • Ex: malonate can block succinate from binding with dehydrogenase during Kreb’s cycle

10. Non-Competitive Inhibition • Non-competitive inhibition is when an inhibitor binds with the enzyme but not at the active site (instead at the allosteric site), however the result can be a change in the shape of the active site • Ex: metal ions like Silver and Mercury bind to sulfur parts of R groups on amino acids which inhibits disulfide bonds and changes shape of proteins Allosteric site

13. End-Product Inhibition • With assembly line metabolic reactions (metabolic pathways) cells have developed a way to regulate enzyme activity so resources and energy are not wasted • When end products are abundant, the metabolic pathway is shut down by inhibiting the action of the 1st enzyme • Usually, inhibition is achieved when final product binds to 1st enzyme at allosteric site • Then, when more product is needed, the 1st enzyme will be reactivated with removal of product at allosteric site