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An Introduction to Metabolism

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Title: An Introduction to Metabolism


1
  • An Introduction to Metabolism

2
Metabolism/Bioenergetics
  • Metabolism The totality of an organisms
    chemical processes managing the material and
    energy resources of the cell
  • Catabolic pathways degradative process such as
    cellular respiration releases energy
  • Exergonic
  • Anabolic pathways building process such as
    protein synthesis photosynthesis consumes
    energy
  • Endergonic

3
Thermodynamics
  • Energy (E) capacity to do work
  • Kinetic energy energy of motion
  • Potential energy stored energy
  • Thermodynamics study of E transformations
  • 1st Law conservation of energy E
    transferred/transformed, not created/destroyed
  • 2nd Law transformations increase entropy
    (disorder, randomness)
  • Combo quantity of E is constant, quality is not

4
Free energy (G)
  • Free energy portion of systems E that can
    perform work (at a constant T)
  • Exergonic reaction net release of free E to
    surroundings (?Glt0) - spontaneous
  • Endergonic reaction absorbs free E from
    surroundings (?Ggt0) NOT spontaneous

5
Gibbs Free Energy Formula
  • ?G ?H - T ?S
  • ?G Gibbs Free Energy, the amount of free
    energy available to a system
  • Unit kJ (kiloJoules)
  • ?H heat of reaction (or Enthalpy), the amount
    of heat energy in a system
  • Unit kJ (kiloJoules)
  • T temperature
  • Unit (Kelvin ? C 273)
  • ?S entropy, the amount of order/disorder in a
    system
  • Unit J/K (Joules per Kelvin)

6
What it means
  • ?G positive vs. negative
  • ?G reaction is endergonic (energy must be
    supplied to make the reaction occur)
  • - ?G reaction is exergonic (generally, this
    reaction is spontaneous and releases energy)
  • ?H positive vs. negative
  • ?H reaction is endothermic (heat energy is
    absorbed from the surrounding area)
  • - ?H reaction is exothermic (heat energy is
    released into the surrounding area)

7
What it means
  • ?S positive vs. negative
  • ?S the entropy of the system in increasing
    (you have more free moving molecules, things are
    breaking apart, catabolism)
  • - ?S the entropy of the system is decreasing
    (you have more structured arrangement of
    molecules, tends to be fewer, more complex,
    molecules, anabolism)
  • EXAMPLE HC2H3O2 has less entropy than 2 H
    (more number of molecules as opposed to just more
    atoms in molecule)

8
EXAMPLE
  • A biological reaction has an exothermic reaction
    (?H) that produces -55.8kJ of energy. If the
    reaction is decreasing entropy (?S) by -0.35kJ/K
    at a temperature of 25C, what would be the free
    energy (?G)? Is this reaction exergonic
    (releasing energy) or endergonic (absorbing
    energy)?

9
SOLUTION
  • ?G ?
  • ?H -55.8kJ
  • ?S -0.35kJ/K
  • T 25C
  • 298K
  • ?G ?H T?S
  • ?G -55.8kJ (298K)(-0.35kJ/K)
  • ?G -55.8kJ 104.3kJ
  • ?G 48.5kJ
  • NOTE The reaction is endergonic

10
QUESTIONS
  • How do you think the following affects Free
    Energy? Does it make it more likely to happen or
    less likely?
  • Increasing the temperature of a system?
  • Decreasing the entropy?
  • Decreasing the enthalpy (heat of reaction)?

11
ENERGETICS AND REACTIONS
  • All reactions need energy to start (Energy of
    activation)
  • Many times this energy cost is insurmountable
  • Strategies to deal with energy cost
  • Couple reaction with another exergonic reaction
  • Enzymes to reduce energy of activation

12
Energy Coupling ATP
  • E coupling use of exergonic process to drive an
    endergonic one (ATP)
  • Adenosine triphosphate
  • ATP tail high negative charge
  • ATP hydrolysis release of free E
  • Phosphorylation (phosphorylated intermediate)
    enzymes
  • KINASES

13
Enzymes LOCK AND KEY MODEL
  • Catalytic proteins change the rate of reactions
    w/o being consumed
  • Free E of activation (activation E) the E
    required to break bonds
  • Substrate enzyme reactant
  • Active site pocket or groove on enzyme that
    binds to substrate
  • Induced fit model

14
Effects on Enzyme Activity
  • Temperature
  • pH
  • Cofactors
  • inorganic, nonprotein helpers ex. zinc, iron,
    copper
  • Coenzymes
  • organic helpers ex. vitamins

15
Rate of enzyme activity
  • There are many actions that can speed up the rate
    of enzyme activity (already discussed)
  • Optimal pH, increased temp, increased amount of
    enzyme, increased amount of substrate
  • Regardless of optimal concentrations, thing
    always limits the enzyme rates
  • Amount of enzyme
  • Once you have maxed out the use of enzymes, the
    rate of reaction is constant

16
Enzyme Inhibitors
  • Irreversible (covalent) reversible (weak bonds)
  • Competitive competes for active site
    (reversible) mimics the substrate
  • Noncompetitive bind to another part of enzyme
    (allosteric site) altering its conformation
    (shape) poisons, antibiotics
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