In amino acid catabolism, the first reaction for many amino acids is a(n):
a. decarboxylation requiring thiamine pyrophosphate (tpp).
b. hydroxylation requiring nadph and o₂.
c. oxidative deamination requiring nad⁺.
d. reduction requiring pyridoxal phosphate (plp).
e. transamination requiring pyridoxal phosphate (plp).

C. oxidative deamination requiring NAD⁺.

Explanation:

Oxidative deamination is the first step in breaking down the amino acids in order to be converted into sugars. This process begins by removal of amino group of the amino acids. The amino group then becomes ammonium as it is lost and subsequently, undergoes the urea cycle to become urea in the liver. From there, It is released into the blood stream, where it is transferred to the kidneys, which will secrete the urea as urine.

The remaining portion of the amino acid becomes oxidized, forming an alpha-keto acid. The alpha-keto acid thus proceed into the Citric acid cycle, in order to produce energy.

The alpha-keto acid can also enter glycolysis, where it will be eventually converted into pyruvate. The pyruvate is then converted into acetyl-CoA so that it can enter the Citric acid cycle cycle and convert the original pyruvate molecules into ATP, or usable energy for the organism.

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.