Question

Ethanol metabolism starves the cell of NAD+ and increases the production of reactive oxygen species. What will be the effect on the TCA cycle, PPP, glycogen metabolism, and beta-oxidation?

Answer 1

1). EFFECT ON TCA cycle

TCA cycle(Krebs cycle) is a series of chemical reactions takes place in the mitochondria of a cell. In all aerobic organism this chemical reaction release stored energy through the oxidation of acetyl-CoA. This acetyl-CoA can be derived from carbohydrates(Glycolysis), fats ($\beta$ Oxidation), and proteins. CO2 is produced and eliminated in TCA cycle. Energy is mainly produced in the form of NADH, FADH and,GTP . ATP is the major energy currency that human can use.

After TCA cycle this energy rich compounds (NADH and FADH2) release electrons to complexes present on the inner mitochondrial membrane and NADH converts to NAD+. Inside the mitochondria, reactive oxygen is present.which will absorbs electron and combine with H+ to form H2O.

From this it is clear that, if reactive oxygen species increases, TCA cycle will also increases. TCA cycle yields large number of NAD+ (End of mitochondrial respiration) which can use in the ethanol metabolism. Ethanol metabolism indirectly increases the TCA cycle

2). EFFECT ON PPP (PENTOSE PHOSPHATE PATHWAY)

PPP is also a metabolic path way similar to Glycolysis. Both oxidative and non oxidative reactions are involved in it. PPP metabolism generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of Nucleotides. In PPP most of the compounds will move to glycolysis then to Kreb's cycle and mitochondrial respiration(ETC) respectively. Major function of this path way is to generate reducing equivalents, in the form of NADPH and for reductive biosynthesis reactions within cells.

In the question it is given that reactive oxygen is produced. It is highly dangerous to body. For the removal it should be converted to H2O. So mitochondrial respiration will increase and uses available NADH. It will produce large number of NAD+.

So Ethanol metabolism indirectly increases the PPP

3). EFFECT ON GLYCOGEN METABOLISM

Glycogen is a  branched polymer of glucose residues stored for further use (When blood glucose level reduces). We know glucose metabolism (glycolysis) yields energy. When body needs energy glycogen metabolism takes place and glycogen is converts to glucose. This glucose will enter in to glycolysis then to Kreb's cycle and mitochondrial respiration(ETC). Here also the same happens as above.

So Ethanol metabolism indirectly increases the GLYCOGEN METABOLISM

4). EFFECT ON $\beta$ OXIDATION

Beta oxidation is the metabolism of fatty acids takes place in mitochondria. It will generate NADH, FADH2 and Acetyl CoA. This Acetyl CoA enter in to Kreb's cycle and then to mitochondrial respiration. Reactive oxygen species is used to generate more NAD+ (Discussed in the cycles above)

Here also Ethanol metabolism indirectly increases the Beta oxidation.