signaling responses

Why do signalling responses that require changes in proteins already present in the cell occur in milliseconds to seconds, whereas responses that involve changes in gene expression usually take hours?

nuclear receptors

Nuclear receptors carry a binding site for a signal molecule and for a DNA sequence. How is it that identical nuclear receptors in different cells can activate different genes when they bind to the same signal molecule?

signal amplification

The signaling mechanisms used by a steroid-hormone receptor and by an ion channel linked receptor have very few components. can either mechanism lead to an amplification of the initial signal? If so, how?

second messengers

Is it true that all small intracellular mediators (second messengers) are water-soluble and pass freely through the cytosol? Why? I know this is true, but why is it true?

intracellular molecule synthesis

two intracellular moleules, A and B, are normally synthesized at a constant rate of 1000 molecules per second per cell. Each molecule of A survives an average of 100 seconds, while each molecule of B survives an average of 10 seconds. A) How many molecules of A and B will a cell contain? B) If the rates of synthesis of both A and B were suddenly increased 10 fold to 10,000 molcules per second-without any change in their average lifetime-how many molecules of A and B would there be after one second? C) Which molecule would be preferred for rapid signalling? why?