L 12 Energy Aerobic

How to measure energy

• Thermodynamically, Energy is order (S, or Entropy)

• Every system seeks to achieve a minimum free energy

• Gibbs energy (G) is energy associated with chemical reaction that can be used to do work

• A reaction with a (-) delta G increased disorder and is favored

• A reaction with a (+) delta G (like forming a peptide bond) creates order and is not favored.

• + delta G reactions do not take place spontaneously

ATP - the biological currency of energy

• ATP is a very ordered

• its hydrolysis to ADP has a (-) delta G value [meausred i kilocalories, or Kcal]

• ATP←_> ADP + Pi, Delta G naut = ~-11kcal

• Cell has ways to couple energy released from this reaction to drive other reactions with postive delta G values

Peptide Bond

• Formation requires energy and is NOT spontaneous

• Must be coupled with GTP hydrolysis

• GTP hydrolysis = -11kcal

How do you get energy?

• autotrophs: use energy from sun (or reduced chemicals) to put order into CO2

• Heterotrophs: eat things from the environment that are already ordered

• Both: Energy in the ordered molecules is released slowly and the stored energy is stored in a form the cell can use later

Making ATP - 2 ways

1. substrate level phosphorylation: high energy compound can transfer its phosphate directly to ADP

2. Oxidative phosphorylation: energy is sued to set up a proton gradient across a membrane which is used to drive an ATP synthase, combining ADP with inorganic phosphate

Substrate level phosphorylation

• high energy compund directly transfers its phosphate to ADP

  • last step in glycolysis

• ex phosphophenolpyruvate transferring phosphate group to ADP upon forming pyruvate

Oxidative phosphorylation

• ATPase engine adds phosphate to ADP

  • uses proton gradients (electron trasnfer grenerate membrane potential)

Oxidation of glucose

As glucose is oxidized, NAD is reduced to NADH

Oxidative phosphorylation (2 components)

1. electron transport chain

2. proton motive force

Electron Transport chain

1. driven by oxidation of reduced compounds

2. energy released from the oxidation of these compounds is coupled to the transport of protons across the membrane

ETC (first step)

1. NADH dehydrogenase releases 2 electrons (-320mV redox potential)

2. Electrons move thorugh several iron-sulfur clusters and a flavoprotein

3. Results in 2 protons pumped

ETC (Second step)

1. ubiquinone binds 2e- to form ubiquinol

2. electrons are donated to cytochrome bc

3. 2 protons deposited outside

ETC (Third step)

1. cytochrome bc passes 2e- to heme b and then to heme c

2. e- are donated to soluble cytochrome c

ETC (Third step)

1. cytochrome c electrons are passed to cytochrome c oxidase

ETC (fifth step)

1. cytochrome c oxidase passes e- to a heme

2. electron passed to O2 to form H2O

3. proton is pumped

Protons per electrons

• 6 protons are pumped for every 2 electrons

Transferring ELectrons (molecules)

1. iron-sulfur clusters

2. heme

3. quinone

4. flavin

Iron sulfur clusters

• Iron-sulfur clusters are inserted into many re-dox proteins

• helf in place by sulfur group of cysteine

• Iron is a good electron carrier ebcause it can easily go from fe2+ to Fe3+ and back

Heme

• Heme groups contain iron within a protoporphryin ring structure

• Heme can be inserted into proteins covalently or non covalently

• heme-containing proteins are called cytochromes

Quinone

• Quinones are hydrophobic hydrocarbons which resise in the membrane

• Carry protons and electrons

Flavoproteins

1. FMN - Flavin mono nucleotide

2. FAD - Flavin adenine dinucleotide

Proton motor force (PMF)

• Storage of energy across cell membrane

  • has both chemical (pH) and electrical(V) potential

Redox potential of electrons

• The lower the redox potential of an electron, the more it wants to lose the electron

Order of redox potentials (6)

1. NADH→ NAD+2e

2. QH→Q(2e)

3. CytB + Fe3^+→CytB+Fe2^+

4. CytC + Fe3^+→CytC+Fe2^+

5. CytA + Fe3^+→CytA+Fe2^+

6. 1/2O + 2e→OH

ATP synthase structure

1. 3 ADP/ATP binding sites between alpha and beta segments (3each)

2. Roatating gamma segment in the center

   1. Fo = integral membrane motor protein

   2. F1 = soluble ATP producing protein

ATP synthase mechanism

1. Spinning motor is attached to a subunit (gamma) that spins inside the souble F1

   1. one nucleotide binding site is empty

   2. one nucleotide binding site contains ADP + Pi

   3. One nucleotide binding sites contains ATP

2. Spinning changes conformations between 3 types

negative delta G reactions

increases disorder → is favored

occurs spontaneously

positive delta G reactions

creates order → not favored

Does not occur spontaneoulsy (msut be coupled with a (-) delta G reaction

Energetic of electron transport

• The reduction/oxidation potential (E) of a chemical reaction can be measureed

• Standard reduction potentials (E naut) are measured in volts

• Calculated relative to standard hydrogen electrode under “standard” conditions (25C, 1M reactants)

• Biologist use Enaut’ = reduction potential at pH=7

• Portons are pumped acorrss the memrbane against the PMF

  • requires energy

• The electron donor is more reduced than the electron acceptor (more reduced=more energy)