The nucleotides that build up the DNA molecule contain the following bases EXCEPT A. guanine
B. adenine
C. cytosine
D. uracil​

correct answer is D.

Explanation:

The nucleic acid is made up of five major nitrogenous bases. These nitrogenous bases are adenine (A), guanine (G), thymine (T), and cytosine (C). Adenine is always paired with thymine, and guanine is always paired with cytosine. These are known as base pairs. Uracil is only present in RNA, by replacing thymine.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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