Question

Odorant molecules activate sensory neurons by

	a.	deflecting the cilia of hair cells, leading to the release of neurtotransmitters.
	b.	binding to rhodopsin, leading to cell depolarization
	c.	passing through ion channels and altering membrane potentials
	d.	binding to membrande-bound receptor proteins of sensory neurons
	e.	altering basilar membrane stiffness to shift response by receptor cells

Hormone X activates the cAMP second messenger system in its target cells. The greatest response by a cell would come from _____.

	a.	applying a molecule of hormone X to the extracellular fluid surrounding the cell
	b.	injecting a molecule of hormone X into the cytoplasm of the cell
	c.	applying a molecule of cAMP to the extracellular fluid surrounding the cell
	d.	injecting a molecule of cAMP into the cytoplasm of the cell

Answer 1

1) Answer is d) binding to membrane bound receptor proteins of sensory neurons.

Olfactory receptors (ORs) belong to the G-protein-coupled membrane bound receptor family which recognize thousands of odorant molecules in the olfactory sensory system. Olfactory signaling is initiated when odorant molecules interact with olfactory sensory neurons. These neurons then express proteins that transform chemical signals carried by odorant molecules into neuronal impulses. Activation of odorant receptors also results in neurochemical effects in different areas of the brain, triggering what we interpret as a smell.

2) Answer is a) applying a molecule of hormone X to the extracellular fluid surrounding the cell.

Hormone X  bind to extracellular surface of the cell and intiate downstream process in which it will activate cAMP in the cytosol for further downstream signalling and cell response.Cell response will be great if hormone is in extracellular fluid because it will increase in concentration and this will lead to activation of more cAMP thus amplifying more cellular response.

Injecting X in cytoplasm will lead to no signalling becuase it has no receptor present in cytoplasm to bind.and so like of cAMP in extracellular fluid will have no signalling because the hormone need to bind to extracellular receptor to activate cAMP. Injecting cAMP in cytoplasm will lead to more conc of cAMP in cytoplasm ,but for that conc of cAMP will need a more amount of X, but the amount of hormone is limited.