Question

Which of the following statements is false? Group of answer choices A) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot directly activate intracellular proteins they must act by affecting membrane lipids. B) Nucleotides and amino acids can act as extracellular signal molecules. C) Some signal molecules are transmembrane proteins. D) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription.

Answer 1

The false statement is A), as nitric oxide (NO) can directly activate intracellular proteins by binding to an intracellular receptor, rather than by affecting membrane lipids.

Step-by-step explanation:

The false statement among these choices is A), because nitric oxide (NO), which is a dissolved gas and acts as a signaling molecule, does not alter membrane lipids but rather can directly activate intracellular proteins.

Specifically, nitric oxide can diffuse freely across cellular membranes due to its gaseous and hydrophobic nature, and it typically binds to an intracellular receptor, leading to a series of intracellular events. The correct expectation for the action of such a gaseous molecule, like NO, would be that it binds to an intracellular receptor.

Another key point to note is that statement D) is true as some signal molecules can indeed bind directly to intracellular proteins that bind DNA and regulate gene transcription. These types of molecules are hydrophobic signaling molecules that readily diffuse across the plasma membrane and frequently act as transcription factors within the cell.

Answer 2

The answer is A.

Step-by-step explanation:

B) Nucleotides and amino acids can act as extracellular signal molecules:

ATP is made of adenosine (a type of nucleotide) and used in cell signalling called "purigenic signalling" and amino acids are also used as signal molecules.

C) Some signal molecules are transmembrane proteins:

Transmembrane acts as receptors for smaller signal molecules so this can also be accepted as true.

D) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription:

That is also true, some of the hormones can cross lipid membrane of the cells and bind directly to the intracellular (inside-of-a-cell) proteins.

Lastly; dissolved gasses such as nitric oxide can activate proteins such as guanylyl cyclase so this choice is false.