Terminal Respiration

Question 1

Why are there electron shuffle systems? .

Answer 1

For oxidation in the terminal respiratory system of eukaryotic cells, NADH and FADH2 have to be in the mitochondrial matrix

The majority of NADH and FADH2 is formed there (citric acid cycle and β-oxidation of fatty acids), but some NADH is formed in the cytoplasm (gycolysis)

Cytoplasmic NADH cannot cross the membrane, shuttle systems be used to pass e-’s on to the electron transport chain within the mitochondria

Question 2

What are the two main electron shuffle systems?

Answer 2

Glycerol-Phosphate shuttle (mainly in brown adipose tissue)
Malate-Aspartate shuttle (in most other cell types)

Question 3

What happens in glycerol phosphate shuffle?

Answer 3

The NADH is unable to cross the membranes of the mitochondria, but G-3-P can, passing it’s e-’s to FADH2

Oxidation of FADH2 in the electron transport chain generates, per mol, less ATP than oxidation of NADH

Thus, an energetic ‘price’ is paid for using cytosolic reduced co-substrates in terminal respiration

Question 4

How is the energy stored up in the hydrogen ion gradient used?

Answer 4

the electron motive force – in this case it is a proton motive force – allows the proton gradient to do work

a molecular turbine has evolved to harness the energy in the proton gradient – ATP synthase

Question 5

What is chemiosmosis?

Answer 5

As e-’s pass through the complexes of the transport chain protons move from the matrix to the outside of the inner mitochondrial membrane

Question 6

What is the protein motive force?

Answer 6

The protons on the outside of the membrane act as a store of potential energy
When these protons are ‘allowed’ to flow back down their gradient they release energy to do work – proton motive force