11/15/06

From Biolk483

  • Exam II is multiple choice.

Contents

ATP (continued)

The energy of ATP

  • Why do we lose -7.3 kcal of energy when we cleave off 1 Pi? Three reasons.
    • Resonance
      • There are 4 possible resonance structures when in ATP form.
      • There are 5 possible resonance structures when in ADP + Pi form.
    • Release of charge stress
      • Net charge on ATP is -3.5
      • Net charge on ADP + Pi is -4, so although there is more charge, it is separated on two separate molecules.
    • Net Hydration
      • We can get more H2O around ADP and Pi than just around ATP. Since ATP and ADP and Pi are polar, they like having lots of H2O around them.
    • These 3 reasons explain why there is such a high dG available from ATP.

High Energy Compounds

  • PEP
    • -14.8 kcal
    • The most energetic
    • Anything can phosphorylate things below it in this chart
  • Carbonyl phosphate
    • -12.3 kcal
    • Seen in urea cycle
  • 1,3 Diphosphoglycerate
    • -11.8 kcal
    • Found in glycolosis
  • Acetyl phosphate
    • -11.3 kcal
    • Seen in prokaryotes
  • Phosphocreatine
    • -10.3 kcal
    • This is a storage form of high energy phosphate.
    • It has a phosphoramidate bond.
  • ATP -> AMP + PPi
    • -10 kcal
  • ATP -> ADP + Pi
    • -7.3 kcal
  • ADP -> AMP + Pi
    • -7.3 kcal

Low energy phosphates

  • AMP -> Adenosine + Pi
    • -3.4 kcal
  • Sugar phosphates
    • -5 through -2 kcal
    • Put the Pi on sugar from ATP to make these low energy holding molecules.
    • We start glycolosis by making one of these sugars.

Example of Pi Movement

  • PEP + ADP -> Pyruvate + ATP, then ATP + glucose ---via hexokinase---> glucose 6 phosphate
  • Storage forms: phospho creatine, phophoargine, polymetaphosphate (primitive)

Bioenergetics in vivo

  • In a cell, the concentration of ATP is far greater than the concentrations of ADP and Pi
    • If this is not the case, it is often because of age or disease
    • Energy Charge: the ratio of ATP to ADP+Pi.
      • If the energy charge is 1, then there is 100% ATP, if 0, all ADP + Pi.
      • 0.8 might be observable in a very run down, in poor health individual. Very near death.
      • The charge is calculated as (0.5[ADP] + [ATP]) / ([AMP] + [ADP] + [ATP])
      • This charge should range form 0.8 to 0.95.

[edit] End of Second Exam Material

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