Chapter 3.2

Question 1

What is meant by the term facilitated diffusion?

Answer 1

• it is a type of passive transport
• > diffusion of molecules down a concentration gradient through a pore in the membrane created by a transmembrane protein

Question 2

What are the three types of ion channels

Answer 2

1) Ungated channels
- >no gates and unregulated

2) Voltage-gated channels
- >the gate is regulated by the membrane potential near the channel
- >closed under resting conditions but membrane depolarization causes a protein conformation change
- >allows them to open and quickly close as the voltage increases

3) Ligand-gated channels
- >binding of a specific substance or ligand to the channel
- >causes it to open or close

Question 3

What are the three domains of the enzyme-linked receptors

Answer 3

1) membrane-spanning domain
- >anchors the receptor in the membrane

2) Ligand-binding domain
- >stimulated by the appropriate ligand
- >induces a conformation change
- >and then activates the catalytic domain

3) Catalytic domain
- >once activated, it results in the initiation of a second messenger cascade

Question 4

Describe the general characteristic of G protein-coupled receptors

Answer 4

• they are integral membrane proteins

- >characterized by seven membrane spanning a-helices

Question 5

How do GPCR transmit their signals to an effector in the cell

Answer 5

-utilize a heterotrimeric G protein

Gi
->inhibits adenylate cyclase(decreasing levels of cAMP)

Gs

• > stimulates adenylate cyclase
• > increases the levels of cAMP

Gq

• > activates phospholipase C
• > end result is increasing calcium levels in the cell