Question

Cell energetics:

a) What is oxidative phosphorylation and where does it occur?

b) What is chemiosmosis and where does it occur?

c) What is the difference between alcohol fermentation and lactic acid fermentation?

Answer 1

a) During the various stages of aerobic respiration, energy rich molecules such as NADH and FADH2 are produced. NADH and FADH2 contains paired electrons. In the last stage of the aerobic respiration high energy electrons donated by the NADH and FADH2 move through various electron carriers and finally reduce molecular oxygen into the water. The high amount of free energy released during the reduction of the molecular oxygen is used by the cells to generate ATP molecules, this process is known as the oxidative phosphorylation.

b) Electrons donated by the NADH and FADH2 move through the various electron carriers in a series of oxidation-reduction reactions. These electron carriers are located on the inner mitochondrial membrane and during the oxidation-reduction reactions the free energy released is used to pump protons from the matrix into the inter membrane space. This proton pumping from the matrix into the inter membrane space generates a electrochemical gradient of protons also known as the proton motive force. Inner mitochondrial membrane has transmembrane protein complexes known as the ATP synthase. When protons move from inter-membrane space into the matrix along their concentration gradient, they move via ATP synthase. Energy of this downhill transport of protons provide energy to the ATP synthase for the conversion of ADP to ATP. This is known as the chemiosmosis hypothesis.

Chemiosmotic synthesis of ATP takes place in mitochondria as well as in the chloroplasts.

c)

Alcohol fermentation	Lactic acid fermentation
Takes place in yeast and the enzyme alcohol dehydrogenase is involved	takes place in the muscle cells and the enzyme lactate dehydrogenase is invo
Carbon dioxide is produced	carbon dioxide is not produced
End products are alcohol and carbon dioxide	End product is lactic acid.