CITRIC ACID CYCLE AND OXIDATIVE

PHOSPHORYLATION

Cellular respiration (Parts 2 and 3)

CITRIC ACID CYCLE In general: Pyruvate (3-C molecule)

enters the mitochondrion, and enzymes oxidize it.

Transition between Glycolysis and CAC: Pyruvate is converted to acetyl CoA. (CO2 is removed)

Like a furnace because of all the oxidizing!

Output per molecule of pyruvate (Remember: 2 per glucose) – 3CO2 , 1 ATP, 1 FADH2 , 4 NADH … carry

high-energy electrons to ETC

CAC: STEPS 1) acetyl group on acetyl CoA

combines with oxaloacetate to form citrate

2) water is removed then added to make isocitrate (isomer of citrate)

3) CO2 is removed and the compound is oxidized (NADH is formed)

4) CO2 is removed and the compound is oxidized and attached to CoA (NADH is formed)

CAC: STEPS 5) CoA is displaced by a phosphate

that is eventually transferred to ADP to make ATP

6) H’s are transferred to FAD to form FADH2

7) water is added to break and form bonds

8) NAD+ is reduced to NADH by oxidizing the substrate to reform oxaloacetate

CO2

ATP

OXIDATIVE PHOSPHORYLATION Now we see how most ATP is made from

energy in food! The “taxis” that escort the electrons from

Glycolysis & CAC to the Electron Transport Chain are NADH and FADH2.

Electron Transport Chain: Made of molecules (mostly proteins) embedded

in the inner membrane of the mitochondrion Many folds (“cristae”) provide more surface area Proteins become reduced when they receive

electrons, then oxidized when they pass on the electrons to their more electronegative neighbor

Free energy decreases with each step

PATHWAY OF ELECTRON TRANSPORT 1. NADH (carrying electrons from

food) releases its electrons to a flavoprotein.

2. The flavoprotein then passes the electrons to an Iron-Sulfur protein.

3. From there, the electrons are transferred to ubiquinone (a mobile, non-protein electron carrier).

PATHWAY OF ELECTRON TRANSPORT 4. Other protein carriers known as

cytochromes then pass the electrons on to oxygen.

5. Oxygen is VERY electronegative, so it readily grabs the electrons as well as hydrogen ions to form water.

*Note: FADH2 adds its electrons at a lower energy level, so it provides less energy for ATP synthesis.

Permits H+ to move down its concentration gradient.

CHEMIOSMOSIS ATP Synthase is a protein complex in the

mitochondrial inner membrane that uses an ion gradient to make ATP.

This gradient (or proton motive force) drives H+ back across the membrane through ATP synthase

Chemiosmosis – the process in which energy stored as a H+ gradient across a membrane drives cellular work (i.e. – generates ATP)

Electron transfers cause protons (H+) to be pumped across the mitochondrial membrane by some members of the ETC.

CHEMIOSMOSIS ATP synthase is composed of a rotor, a

knob , a rod, a stator ATP synthase’s rotor spins as H+ pass

through it, then the knob’s enzymes are activated by conformational changes

Total = 36-38 ATP produced from 1 glucose