Bioenergetics of the cell

Definition of bioenergetics
1. Part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the molecules found in biological organisms
2. It can also be defined as the study of energy relationships and energy transformations in living organisms
Gibbs' free energy
1. For any process to be possible, the change in Gibbs' free energy must be negative
2. A negative Gibbs' free energy indicates a 'spontaneous' process
3. Spontaneity does not imply that the reaction goes ahead, it simply considers the possibility, or feasibility, of a particular reaction or process
4. 'Free' indicates the energy available in the form of useful work
5. Sometimes a catalyst is required
6. OILRIG
  1. Oxidation is losing [electrons]
  2. Reduction is gaining [electrons]
7. Change in Gibbs' free energy - energy is liberated and available for use
8. Change in Gibbs' free energy depends on difference in energy between products and substrates
9. Change in Gibbs' free energy for ATP hydrolysis
  1. ATP + H20 >> ADP + Pi
    1. Gibbs' change in free energy is -7.3kcal/mole
  2. Equimolar solution of product and substrate favours the forward reaction (hydrolysis of ATP)
    1. Change in Gibbs' free energy is negative
10. Change in Gibbs' free energy outside standard conditions depends on product and substrate concentrations
  1. Reactions positive change in Gibbs' free energy can occur in the forward direction if there is enough substrate or if product is reduced significantly
  2. Product can be very low if it is rapidly used in another reaction
11. Change in Gibbs' free energy values of sequential reactions are additive
Structure of ATP
1. Adenine
2. Ribose
3. Phosphate
4. Has 2 phosphoanhydride bonds
  1. When the 1st is hydrolysed it produces ADP
  2. When the 2nd is hydrolysed it produces AMP
Phosphoanhydride bonds are relatively weak
1. Overall, more energy is released in forming the products than used to break bonds in the reactants
Uses of ATP
1. Mechanical work
  1. Muscle contraction
    1. Direct hydrolysis of ATP is the source of energy in the conformational changes in myosin that produce muscle contraction
    2. The binding of ATP dissociates myosin from actin
    3. ATP is hydrolysed, inducing a conformational change that displaces the myosin head group
    4. The myosin head binds to the new position on the actin filament with the release of ADP and Pi
    5. The return of myosin head to its original conformation drives actin filament sliding
  2. Quick synthesis of ATP
    1. Phosphocreatine serves as a ready source of phosphoryl groups for the quick synthesis of ATP from ADP
    2. The phosphocreatine concentration in skeletal muscle
    3. Creatine kinase catalysis this reversible reaction
2. Keeping us alive
  1. Transport e.g. sodium / potassium transporter
    1. Membrane active transport
    2. Accounts for 10-30% of BMR in humans
    3. The pump binds ATP and binds 3 intracellular NA+ ions
      1. ATP is hydrolysed
        Conformational change in the pump which exposes the Na+ ions to the outside
        The phosphorylated form of the pump has a low affinity for Na+ ions, so they are released to the cell exterior
        The pump binds 2 extracellular K+ ions
        Dephosphorylation of the pump occurs, and K+ is transported into the cell
        The unphosphorylated form of the pump has a higher affinity for Na+ ions than K+ ions, so the 2 bound K+ ions are released
        ATP binds, and the process starts again
    4. Functions
      1. Establish an intracellular ion environment high in K+ and low in Na+
      2. Control of cell volume
      3. Providing electrochemical sodium gradient for driving secondary active transport systems e.g. glucose
      4. Establish a resting potential
  2. Anabolic or synthetic reactions
    1. Glycogen synthesis
    2. Fatty acid synthesis
    3. DNA synthesis
    4. Protein synthesis
    5. Cell division
ATP regeneration
1. There is a set amount of ATP in the body at any one time
  1. ~100mg worth
2. If we were unable to regenerate ATP, in the heart it would last for 10 heart beats
3. ATP generation
  1. Glycolysis
  2. Fatty acid oxidation
  3. Ketone acid oxidation
  4. Citric acid cycle (TCA cycle)
  5. Pentose phosphate pathway
  6. Individual pathways for individual pathways
4. Substrate level phosphorylation
5. Anaerobic glycolysis
6. Requires a source of energy
7. A controlled series of chemical reactions
8. Intermediates NADH and FAD2H produced
  1. Glycolysis
  2. Krebs cycle
9. Creates some ATP directly or via electrons

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Bioenergetics of the cell

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	Created by Alice Patterson about 9 years ago