Bio Lecture 4

Lecture 4 Objectives

1. Describe receptor molecules for protein, peptide, and catecholamine hormones and how they are arranged in the plasma membrane of the target cell

a. These hormones cannot cross the membrane because they are water soluble so they exert their actions by binding to cell surface receptor proteins

b. Structural regions

i. Extracellular domain: pokes out into the extracellular fluid and binds to the hormone

ii. Transmembrane domain: is embedded within the plasma membrane

iii. Intracellular domain: projects inside the cell and is therefore in contact with the cytoplasm. May initiate the cascade of events that leads to the formation of a second messenger

2. Describe how the binding of a hormone such as epinephrine to its receptor can modulate the activity of an enzyme or ion channel

c. Hormone attached to the receptor and can initiate the cascade of events that form a second messenger. See page 67

3. Define a G-protein coupled receptor and how it affects the concentration of second messengers in the cell

d. G-proteins are activated when the hormone binds to its receptor, triggering off a cascade of events that generates second messengers.

e. The part of the receptor inside the cell changes shape and becomes a binding site for G-protein, which has GDP attached to it. G-protein then released the GDP and binds to GTP instead. The G-protein and the GTP act via second messengers to work on targets such as enzymes and ion channels

4. Describe what is meant by a second messenger and name 3

f. Substances within the cell that are triggered by the activation of G-proteins

g. 3 examples

iv. Cyclic adenosine monophosphate (cyclic AMP or cAMP)

v. Inositol triphosphate (IP3)

vi. Diacylglycerol (DAG)

5. Describe how a cholera infection can lead to death from hypovolemic shock

h. Cholera is caused by a bacterium that is a product...