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Understanding Enzymes in Cellular Energy Flow

This lecture delves into enzymes as biological catalysts, activation energy, and energy carriers in cellular processes. Topics include enzyme regulation, metabolic pathways, and the impact of environmental factors on enzyme activity.

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Understanding Enzymes in Cellular Energy Flow

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  1. Biology 102 Lecture 11: Energy Flow in Cells (Part 2)

  2. Lecture outline • Brief review of chemical reactions and energy flow (from previous lecture) • Activation energy and the rate of chemical reactions • Enzymes: biological catalysts • Enzyme structure and function • Regulation of enzyme levels

  3. 1. Review of chemical reactions • What is a chemical reaction? • Making and breaking of chemical bonds • Implications of the second law: • Orderly reactants to less ordered products releases energy (EXERGONIC) • Examples…

  4. Implications of the second law (cont.) • Less ordered reactants to more orderly products requires energy (ENDERGONIC) • Examples…

  5. Energy carriers • ATP is the principle energy carrier that allows coupling of reactions • ATP produced during an exergonic reaction provides energy to for endergonic reactions • Bonds easily formed for easy energy transfer from a high energy compound to ATP • Bonds are unstable to easily give up energy in a reaction • Electron carriers such as NADH also carry energy along with electrons

  6. Coupled reactions within living cells ATP is the principle energy carrier that allows coupling of reactions

  7. Electron carriers Electron carriers such as NADH also transfer energy, along with electrons, between exergonic and endergonic reactions

  8. 2. Activation energy and the rate of chemical reactions • Initial input of energy required to start reactions (both exergonic and endergonic)

  9. Will a reaction occur? • Low activation energy: reaction will occur spontaneously • High activation energy: reaction requires something else to get it over the activation energy hump… • Temperature increase • Enzymes • NOTE: Understand how these work in different ways!

  10. 3. Enzymes: Biological catalysts • Example of a metabolic pathway

  11. What does a catalyst do? • Decreases activation energy

  12. Principles of all catalysts • Speed up reactions • Speed up only reactions that would occur anyway, but at a slower rate • Not consumed or permanently changed in the reaction

  13. Enzymes: Biological catalysts • Have all the properties of other catalysts • Are proteins! • Are highly specific for particular “substrates” (reactants) • Examples

  14. Structure of an enzyme • 3-dimensional structure • Think about versatility of proteins • Active site

  15. Cycle of enzyme-substrate reactions

  16. Key points • Active site highly specific for the particular reactants • Conformational change brings together reactants into the correct position to bond • Enzyme allows for the capture of energy in exothermic reactions, and use of energy in endothermic reaction • One enzyme can catalyze many reactions

  17. Regulation of enzymes • Importance of regulation • Types of regulation • Regulation of synthesis • Regulation of protein activation • Feedback inhibition

  18. Mechanisms of inhibition • Allosteric inhibition: • Bind at a different site than the substrates • Negative feedback can work this way • Competitive inhibitors: • Bind directly at the active site • Some poisons act this way

  19. Impact of the environment on enzymes • pH • Can activate or inactivate • Example: Pepsin (pH=2 in stomach) • Salt • Disruption of 3-D structure • Temperature • Direct effects on reaction rates • Denaturation of proteins (2-D, 3-D or 4-D structure) • Coenzymes

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