Kreb's cycle and ETC

1st step of Kreb’s Cycle

Acetyl CoA joins with a 4 carbon molecule to release the CoA and form Citrate, a 6 carbon molecule

2nd step of Kreb’s Cycle

Citrate is turned into isocitrate; removal and addition of H2O

3rd step of Kreb’s cycle

Isocitrate is oxidized, leading to the release of CO2 and leaving a 5C molecule. NAD+ is reduced to NADH. Enzyme involved is called isocitrate dehydrogenase, which has to do with the speed of the cycle.

4th step of Kreb’s Cycle

The 5 carbon is oxidized, reducing NAD+ to NADH and releasing CO2. The 4 carbon left is called succinate, which picks up coenzyme A. Catalyzed by Alpha ketoglutarate dehydrogenase.

5th step of Kreb’s Cycle

CoA is replaced by a phosphate group that is transformed to make ADP into ATP, or GDP to GTP

6th step of Kreb’s Cycle

Succinate is oxidized, creating a 4 carbon called fumarate. The 2 H and e- are transferred to FAD to make FADH2. E- is transferred into ETC.

7th step of Kreb’s cycle

H2O is added to fumarate into Malate

8th step of Kreb’s cycle

Oxaloacetate is regenerated by oxidation of malate and NAD+ reduced to NADH.

Net products of Kreb’s cycle (for One CoA; one glucose produces two Acetyl CoA)

2 carbons enter from acetyl CoA, 2 Co2 released

3 NADH and one FADH2 are generated

One molecule of ATP/GTP produced

Electron Transport Chain

Electrons from NADH and FADH2 travel through the chain of higher to lower energy levels, moving from less electron hungry to more leectron humgry molecules. Energy is released from the transfer and is used to pump protoms from the mitochondrial matrix to the intermembrane space forming a proton gradient.

NADH in ETC

Good at donating because electrons are at a high energy level, so it can put electrons into complex 1 turning into NAD+. electrons move thorugh complex 1 releasing energy, which is then used to pump protons from the matrix into the intermembrane space.

FADH2 in ETC

FADH2 cannot donate electrons, so it does not transfer electrons to complex 1. Instead, it feeds electrons through complex 2, which does NOT pump protons across the membrane.

After two complexes, NADH and FADH2 travel the same route:

Electrons are passed to a carrier called ubiquinone, which reduces to QH2 and delivers to complex 3. In complex 3, more H+ ions are pumped across the membrane, and the electrons are ultimately delivered to another carrier called cytochrome C. C carries the electrons to complex 4, where a final batch of H+ ions is pumped across the membrane.

After Complex 4, electrons are:

passed to O2, which splits into two oxygen atoms and accepts protons from the matrix to form water. Four electrons are required to reduce each molecule O2 into two water molecules.

In the inner mitochondrial membrane:

H+ ions have to go through ATP synthase, which catalyzes the addition of ADP and capturing energy from the proton gradient as ATP.

Chemiosmosis

Energy from a proton gradient is used to make ATP.

What happens to the energy stored in the proton gradient if it weren’t used to synthesize ATP or do other cellular work?

Released as heat.

ETC requires

10 NADH and 2 FADH2

ETC expels

NADH=3 ATP

x10=30 ATP

FADH2=2 ATP

x2=4 ATP

=34 ATP max from oxidative phosphorylation

—

+2 ATP from glycolysis

+2 ATP from citric acid cycle

= 38 ATP from one glucose

ATP synthase is

associated with the ETC- Coupled