Question

5. True/False –regarding receptor proteins (RP) (10 pts)

A) RPs exhibit specificity, saturation, and competition, similar to carrier proteins.

B) RPs may be peripheral membrane proteins or may be nuclear or cytosolic proteins.

C) RPs function as the sensors in reflex pathways.

D) Activated RPs may repress rather than upregulate a gene.

E) Upregulation or downregulation of RPs occurs via receptor number.

Answer 1

Ans:

1. True

2. True - Receptor proteins are located in the cytoplasm, cell membrane, or nuclear membrane. 1. Cytoplasmic receptor proteins include those that respond to steroid hormones. Ligand activated receptors may enter the cell nucleus where they modulate gene expression

3. True - Receptor- Protein molecule usually found embedded within the plasma membrane surface of a cell that receives chemical signals from outside the cell. 2. Sensory nerve- Carries the message from sensory neuron to spinal cord.

4. True -  An example of downregulation is the cellular decrease in the expression of a specific receptor in response to its increased activation by a molecule, such as a hormone or neurotransmitter, which reduces the cell's sensitivity to the molecule. This is an example of a locally acting (negative feedback) mechanism.

5. Receptor regulation :

Cells can increase (upregulate) or decrease (downregulate) the number of receptors to a given hormone or neurotransmitter to alter their sensitivity to different molecule. This is a locally acting feedback mechanism.

Change in the receptor conformation such that binding of the agonist does not activate the receptor. This is seen with ion channel receptors.

Uncoupling of the receptor effector molecules is seen with G-protein couple receptor.

Receptor sequestration (internalization). e.g. in the case of hormone receptors.