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Ground Rules of Metabolism

Explore the foundational concepts of energy and enzymes in cellular metabolism. Learn how energy disperses, the laws of thermodynamics, one-way flow of energy, reactions, and the role of ATP as the cell's energy currency. Discover how enzymes facilitate reactions, factors influencing their activity, and the importance of cofactors. Gain insights into how substances react and the critical role of enzymes in cellular processes.

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Ground Rules of Metabolism

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  1. Ground Rules of Metabolism Chapter 6 Part 1

  2. Impacts, Issues:A Toast to Alcohol Dehydrogenase • In the liver, alcohol dehydrogenase helps break down toxic alcohols, but at the expense of liver function and energy metabolism( 12oz beer, 5oz wine, 1oz of vodka all have the same effects on the liver)

  3. Energy Disperses • First law of thermodynamics • Energy is neither created nor destroyed (goes back into the evnrionment as heat), but can be transferred from one form to another • Second law of thermodynamics • Entropy (a measure of dispersal of energy in a system) increases spontaneously ( Ex.Heat/pan) • Energy is converted from a more concentrated form to a less concentrated form when energy is transferred.

  4. One Way Flow of Energy • The total amount of energy available in the universe to do work is always decreasing • Each time energy is transferred, some energy escapes as heat; thermal energy decreased (not useful for doing work) • Potential energy can be converted to kinetic energy, ATP in muscle cells (mechanical energy) gives up potential energy to contractile units, chemical energy is converted to kinetic energy.

  5. Energy In, Energy Out • Reaction • A chemical change that occurs when atoms, ions, or molecules interact • Reactant • Atoms, ions, or molecules that enter a reaction • Product • Atoms, ions, or molecules remaining at the end of a reaction

  6. Reactants Products 2 H2 (hydrogen) O2 (oxygen) 2 H2O (water) + 2 oxygen atoms 4 hydrogen atoms Fig. 6-6, p. 96

  7. Reactions Require or Release Energy • We can predict whether a reaction requires or releases energy by comparing the bond energies of reactants with those of products • Endergonic (“energy in”) • Reactions that require a net input of energy (Ex. Photosynthesis) • Exergonic (“energy out”) • Reactions that end with a net release of energy (Ex. Cellular Respiration)

  8. Why the World Doesn’t Go Up in Flames • Activation energy • The minimum amount of energy needed to get a reaction started or to proceed on its own.

  9. ATP – The Cell’s Energy Currency • ATP (adenosine triphosphate) • A nucleotide with three phosphate groups • Gives up a phosphate group and energy to other molecules • Primes stable molecules to react (Ex. PGA gives up a P group to ADP • Made by all cells • Phosphorylation • A phosphate-group transfer

  10. adenine AMP ADP ATP ribose P P P B The molecule is called ATP when it has three phosphate groups. After it loses one phosphate group, the molecule is called ADP (adenosine diphosphate); after losing two phosphate groups it is called AMP (adenosine monophosphate). Fig. 6-9b, p. 97

  11. Animation: Mitochondrial chemiosmosis

  12. 6.3 How Enzymes Make Substances React • Enzyme • A catalyst that makes a reaction occur much faster than it would on its own • Enzymes are not consumed or changed by participating in a reaction • Most are proteins (organic molecules, some are RNA • Are very specific and have special shapes • Substrate • The specific reactant acted upon by an enzyme

  13. How Enzymes Work • Enzymes lower the activation energy required to bring on the transition state, when substrate bonds break • Active sites • A groove in the structure of the enzyme where substrates bind and reactions proceed

  14. Transition state Activation energy without enzyme Activation energy with enzyme Free energy Reactants Products Time Fig. 6-11, p. 98

  15. Transition state Activation energy without enzyme Activation energy with enzyme Free energy Reactants Time Products Stepped Art Fig. 6-11, p. 98

  16. Animation: Activation energy

  17. Mechanisms of Enzyme-Mediated Reactions • Binding at enzyme active sites may bring on the transition state by four mechanisms • Helping substrates get together they will react • Orienting substrates in positions that favor reaction • Inducing a fit between enzyme and substrate (induced fit model- enzyme sqeezes the substrate)

  18. Effects of Temperature, pH, and Salinity • Raising the temperature boosts reaction rates by increasing a substrate’s energy • But very high temperatures denature enzymes • Optimum temperature (37-40°celcius) • Each enzyme has an optimum pH range (6-8)

  19. Help from Cofactors • Cofactors • Atoms or molecules (other than proteins) that are necessary for enzyme function • Coenzymes • Organic cofactors such as vitamins • Examples: NAD and FAD

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