11/15/06

From Biolk483

• Exam II is multiple choice.

Contents 1 ATP (continued) 1.1 The energy of ATP 2 High Energy Compounds 3 Low energy phosphates 4 Example of Pi Movement 5 Bioenergetics in vivo 5.1 End of Second Exam Materail

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
• Phospho creatin
  • -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

• ADP -> AMP + 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.

End of Second Exam Materail