The substance that acts as a second messenger at the cellular level is:

1.)The substance that acts as a second messenger at the cellular level is:
a. ATP
b. adenyl cyclase
c. cyclic AMP
d. hormones

2. steroids are able to pass easily through a target cell's plasma membrane because they are:
a. synthesized from amino acids
b. synthesized from carbohydrates
c. lipid-soluble
d. synthesized from nucleic acids

c. cAMP
ATP is obviously not correct. Adenylyl cyclase is used in the system, but causes AMP to cAMP conversion. Hormones wouldn't be secondary.


c. lipid soluble
Steroids are made from sterols which aren't amino acids at all. They are made from the middle chain of triglycerides. Anyway, hormones made from amino acids couldn't cross the membrane because they are polar, actually charged. B is also incorrect because they too are not made from sterols and are even more polar. D also is wrong for the same reason.

1. C.

A G-protein stimulates adenylyl cyclase to produce cAMP, which than activates protein kinase to cause a phosphorylation cascade.

It is a secondary messenger because another protein (G-protein) is required to activate it.

2. C.

The membrane is made of lipids (as are steroids). Something that is lipid-soluble can freely move in a lipid environment.