Question

1.The impossibility of zero-­calorie beer

Ethanol that we consume is oxidized to acetate in the liver, which is then converted to acetyl-CoA and further metabolized to 2 CO2. Determine how many molecules of ATP (or equivalent) are produced from the complete oxidation of one molecule of ethanol to 2 CO2.

Assume that 1 ATP molecule is consumed to form acetyl-­CoA from acetate and CoA

• Reactions for the metabolism of ethanol to acetate are in the textbook,p.342.

•Use P:O ratios of 2.5 ATP per NADH and 1.5 ATP per for QH2

Show your reasoning!

Answer 1

In the presence of enzymes alcohol dehydrogenase and acetaldehyde dehydrogenase, ethanol is converted into acetaldehyde and acetate respectively and both use NAD⁺ and oxidant.

Therefore in the cytosol, 2 NAD are produced. Depending on the movement of electrons into the mitochondria, 1.5 ATP are produced per NADH, so conversion of ethanol into acetate 3 ATP are produced.

During conversion of ethanol into acetyl-CoA, further produced 2CO₂ and 1 ATP molecule. Complete oxidation of acetyl-CoA in the TCA cycle produced 10 ATP molecules in which

3 NADH produced 2.5 ATP each;

1 FADH2 produced 1.5 ;

1 GTP

Ethanol oxidation thus produced= 11 ATP or

                                                    =11 ATP/2 carbons

                                                        = 5.5 ATP/ carbon