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Chapter 8. An Introduction to Metabolism. Objectives Distinguish between the following pairs or terms: catabolic and anabolic pathways; kinetic and potential energy; open and closed systems; exergonic and endergonic reactions

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Objectives

      • Distinguish between the following pairs or terms: catabolic and anabolic pathways; kinetic and potential energy; open and closed systems; exergonic and endergonic reactions
      • Explain how the nature of energy transformations is guided by the two laws of thermodynamics
      • Describe how ATP functions as the universal energy shuttle in cells
      • Describe the structure of enzyme-substrate interactions and how enzymes catalyze biological reactions
introduction
Introduction
  • Characteristics of organisms are all the end-products of the chemical reactions that occur in their cells
  • The cell is a mini factory
    • Roughly 8.64 x 1026 reactions per day
    • Chemical reactions carried out for the purpose of energy transformation or making necessary substances
energy the capacity to do work
Energy-The Capacity to do Work
  • Energy is described and measured by how it affects matter
  • Two types of energy:
    • kinetic-energy of motion
    • potential-stored energy because of structure or location
    • Example: the energy stored in chemical bonds
laws of energy conservation
Laws of Energy Conservation
  • Thermodynamics = study of energy transformations

Two laws govern energy transformation:

    • First law (energy conservation)
      • total amount of energy in universe is constant
        • can be transferred or transformed but cannot be created or destroyed
    • Second law (entropy-disorder- increases)
      • every energy transformation increases entropy
        • energy available for doing useful work decreases with every transformation
organization of the chemistry of life into metabolic pathways
Organization of the Chemistry of Life into Metabolic Pathways
  • Metabolism transforms matter and energy
    • Subject to the laws of thermodynamics
      • Metabolism is the sum of an organism’s chemical reactions
  • Metabolic pathway has many steps that begin with a specific molecule and end with a product
    • Each step catalyzed by a specific enzyme
catabolic vs anabolic
Catabolic vs. Anabolic
  • Catabolic: break down complex molecules into simpler compounds
    • Releases energy
  • Anabolic: build complicated molecules from simpler ones
    • Consumes energy
g gibbs free energy
G = Gibbs Free Energy
  • (Delta) G = Free energy available to do work in a cell
  • A - G means a rxn gives off energy; it provides power
  • A + G means a rxn needs energy; it will not run unless energy is first added
  • Every rxn has a specific G
energy relationships in living things
Energy Relationships in Living Things
  • Chemical reactions in cells either store or release energy
    • endergonic reactions require input of energy
      • energy input equals difference in potential energy between reactants and products

exergonic reactions release energy

      • energy released equals difference in potential energy between reactants and products
    • cellular metabolism is sum total of all endergonic and exergonic reactions in cells
energy relationships
Energy Relationships
  • ATP is cell’s energy shuttle
    • most cell reactions require small amounts of energy
    • food storage molecules contain large amounts of energy
    • energy in food molecules converted to energy in ATP
      • one food molecule=many ATP (e.g. 1 x glucose=36 ATP)
energy relationships1
Energy Relationships
  • Hydrolysis of ATP releases energy
    • Most energy is located in the covalent bond between 2nd and 3rd phosphate groups
    • easily hydrolyzed
    • forms ADP and phosphate group
    • ATP ADP + Pi ( means PO4 = phosphate)
atp synthesis
ATP synthesis
  • endergonic reactions of cellular respiration phosphorylate ADP-reforms ATP
  • ADP + Pi (PO4 = phosphate) ATP
  • More about this in Chapter 9
enzymes
Enzymes
  • Enzymes are large protein molecules that act as biological catalysts
  • Energy of activation (EA) is “energy barrier”, amount of energy needed to start a reaction
  • Enzymes can lower energy barriers = EA
  • Enzymes cannot lower G!
enzyme process
Enzyme Process
  • Specific enzymes catalyze each cell reaction
    • reactant=substrate
    • reactant binds to enzyme active site
    • substrate converted to product
    • enzyme unchanged and releases product
enzymes and denaturation
Enzymes and Denaturation
  • Factors that affect enzyme activity
    • temperature
    • pH
    • salt concentration ( ions)
    • presence of co-factors
    • These factors may lead to denaturation
    • Denaturation = disruption of the enzyme structure due to adverse conditions
    • Example: PH to high or low
question how do you stop enzyme activity but not destroy the enzyme answer inhibition
Question: How do you stop enzyme activity but not destroy the enzyme? Answer: Inhibition
  • Inhibitors block enzyme action,
    • competitive inhibitors-bind to active site
    • noncompetitive inhibitors-bind to second site on enzyme
    • negative feedback-inhibition by product of reaction
  • some pesticides and antibiotics function by inhibiting enzymes
  • Inhibitors most often work on a temporary basis
  • BUT>>>>>>>
checklist
Checklist
  • What is energy?
  • What are the types of energy?
  • What are the laws of thermodynamics?
  • Catabolic vs anabolic?
  • What is ∆G?
  • + ∆G means what? - ∆G means what?
  • What do these look like graphed?
  • What are enzymes? What do they do?
  • Do enzymes change the ∆G?