<span>Two of the nitrogenous bases present in DNA (Guanine and Adenine) contain two rings and thus are much larger than the other two (Cytosine and Thymine), which have only one.
Nitrogenous bases with two rings (such as G and A) are known as PURINES, whereas nitrogenous bases with a single ring (such as C and T) are known as PYRIMIDINES.
A stable DNA structure is formed ONLY when the two strands are a constant distance
apart which ONLY happens when a PURINE (G or A) on one strand is paired with a PYRIMIDINE (C or T) on the other strand. The strands would have to move much further apart to permit a purine to pair with another purine and would have to move much closer together to permit a pyrimidine to pair with a pyrimidine.
(Source: https://www.amherst.edu/system/files/media/1536/ModGen_1C_TP.pdf )</span>
Explanation:
anaerobic respiration would be used when the body has inefficient of 
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Similar to the conversion of pyruvate to acetyl-CoA, each pyruvate molecule loses a carbon atom with the release of carbon dioxide. During the decomposition of pyruvate, electrons move to NAD + to produce NADH. It is used by cells to produce ATP.
- NADH: Three molecules are produced in the Kleb circuit
- FADH2: One molecule is produced in the Kleb circuit
- ATP or GTP: From each molecule of pyruvate during the conversion of succinyl-CoA to succinic acid Two molecules of ATP are produced. The presence of the enzyme succinyl-CoA synthetase.
Learn more about conversion of pyruvate here:brainly.com/question/4198225
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