The direct regulators of differential gene expression are typically

transcription factors.
enzymes.
signaling molecules.
cell surface receptors.

The correct answer is: transcription factors.

Gene expression is controlled (regulated) on different levels (DNA structure, transcription, RNA processing, post-translational modification. Gene expression is regulated in order to increase or decrease the production of specific gene products.

Transcription factors can enhance the interaction between RNA polymerase and a DNA sequence- promoter, encouraging the expression of the gene. Such transcription factors are called activators. Otherwise, when the gene expression is inhibited, factors are called repressors and they bind to sequence –operator.

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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