chapter 6

  1. Energy:
    the capacity to do work
  2. -kinetic energy:
    the energy of motion
  3. -potential energy:
    stored energy
  4. Energy can take many forms:
    • mechanical electric current
    • heat light
  5. Most forms of energy can be converted to
    heat energy.
  6. Heat energy is measured in
  7. One calorie =
    the amount of heat required to raise the temp of water by 1oC
  8. 1 kilocalorie (kcal) =
    1000 calories
  9. Potential energy stored in
    chemical bonds can be transferred from one molecule to another by way of electrons.
  10. oxidation:
    loss of electrons
  11. reduction:
    gain of electrons
  12. redox reactions are
  13. coupled to each other.
  14. First Law of Thermodynamics –
    • energy cannot be created or destroyed
    • -energy can only be converted from one form to another
    • For example:
    • sunlight energy chemical energy
    • photosynthesis
  15. Second Law of Thermodynamics:
    • disorder is more likely than order
    • entropy: disorder in the universe
    • The 2nd Law of Thermodynamics states that entropy is always increasing.
  16. Free energy:
    • the energy available to do work
    • -denoted by the symbol G (Gibb’s free energy)
  17. enthalpy:
    • energy contained in a molecule’s chemical bonds
    • free energy = enthalpy – (entropy x temp.)
    • G = H - TS
  18. Chemical reactions can create changes in free energy:
    DG = DH - T DS
  19. When products contain more free energy than reactants –
    DG is positive.
  20. When reactants contain more free energy than products –
    DG is negative.
  21. Chemical reactions
    can be described by the transfer of energy that occurs
  22. endergonic reaction:
    • a reaction requiring an input of energy
    • - DG is positive
  23. exergonic reaction:
    • a reaction that releases free energy
    • - DG is negative
  24. activation energy:
    • extra energy needed to get a reaction started
    • -destabilizes existing chemical bonds
    • -required even for exergonic reactions
  25. catalysts:
    substances that lower the activation energy of a reaction
  26. ATP = adenosine triphosphate
    -the energy "currency" of cells
  27. ATP structure:
    • -ribose, a 5-carbon sugar
    • -adenine
    • -three phosphates
    • ATP stores energy in the bonds between phosphates.
  28. Phosphates are highly negative, therefore:
    • -the phosphates repel each other
    • -much energy is required to keep the phosphates bound to each other
    • -much energy is released when the bond between two phosphates is broken
  29. When the bond between phosphates is broken:
    • ATP ADP + Pi
    • energy is released
    • ADP = adenosine diphosphate
    • Pi = inorganic phosphate
    • This reaction is reversible.
    • The energy released when ATP is broken down to ADP can be used to fuel endergonic reactions.
    • The energy released from an exergonic reaction can be used to fuel the production of ATP from ADP + Pi.
  30. Enzymes:
    • molecules that catalyze reactions in living cells
    • -most are proteins
    • -lower the activation energy required for a reaction
    • -are not changed or consumed by the reaction
    • Enzymes interact with substrates.
  31. substrate:
    molecule that will undergo a reaction
  32. active site:
    • region of the enzyme that binds to the substrate
    • Binding of an enzyme to a substrate causes the enzyme to change shape, producing a better induced fit between the molecules.
  33. Multienzyme complexes offer certain advantages:
    • 1. The product of one reaction can be directly delivered to the next enzyme.
    • 2. The possibility of unwanted side reactions is eliminated.
    • 3. All of the reactions can be controlled as a unit.
    • Not all enzymes are proteins.
    • Certain reactions involving RNA molecules are catalyzed by the RNA itself.
  34. ribozymes:
    • RNA with enzymatic abilities
    • For example, the ribosome is a ribozyme.
  35. Enzyme function is affected by its environment.
    • Factors that can change an enzyme’s 3-dimensional shape can change its function.
    • -for example, pH, temperature, regulatory molecules
  36. Temperature
    • -enzyme activity may be increased with increasing temp, up to the temp optimum
    • -temperatures too far above the temp optimum can denature the enzyme, destroying its function
  37. pH –
    most enzymes prefer pH values from 6 to 8.
  38. Inhibitors
    are molecules that bind to an enzyme to decrease enzyme activity.
  39. -competitive inhibitors
    compete with the substrate for binding to the same active site
  40. -noncompetitive inhibitors
    bind to sites other than the enzyme’s active site
  41. Allosteric enzymes
    • exist in either an active or inactive state.
    • -possess an allosteric site where molecules other than the substrate bind
  42. allosteric inhibitors
    bind to the allosteric site to inactivate the enzyme
  43. allosteric activators
    bind to the allosteric site to activate the enzyme
  44. Metabolism:
    all chemical reactions occurring in an organism
  45. Anabolism:
    chemical reactions that expend energy to make new chemical bonds
  46. Catabolism:
    chemical reactions that harvest energy when bonds are broken
  47. Some enzymes require additional molecules for proper enzymatic activity.
    These molecules could be:
    • -cofactors:
    • usually metal ions, found in the active site participating in catalysis
    • -coenzymes:
    • nonprotein organic molecules, often used as an electron donor or acceptor in a redox reaction
  48. Biochemical pathways
    • are a series of reactions in which the product of one reaction becomes the substrate for the next reaction.
    • Biochemical pathways are often regulated by feedback inhibition in which the end product of the pathway is an allosteric inhibitor of an earlier enzyme in the pathway.
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chapter 6