Cellular And Molecualr Bases 3

Question 1

Describe location of receptors.

Answer 1

• a receptor is a molecule that receives chemical signals from the outside of the cell
• two locations of receptors are :
  1. Cell surface = hydrophilic signal molecules
  2. Intracellular = cytoplasms & nucleus ( hydrophobic signal molecules )

Question 2

List 3 most common cell surface receptors

Answer 2

1. Ligand Gated ion channel
2. G protein coupled receptor
3. Enzyme coupled receptors
   — a. Receptor tyrosine kinase (RTK)
   — b. Cytokine receptors

Question 3

List the most important second messengers.

Answer 3

• second messengers are intracellular signaling molecules generated in large amounts in response to receptor activation
• Most important second messages are :
  1. Diacylglycerol (DAG)
  —> water insoluble molecule
  —> diffuses from plasma membrane to intermembrane space where it can reach and regulate membrane associated effector proteins
  2. Cyclic Adenosine Monophosphate (cAMP) *
  3. Inositol 1,4,5-trisphosphate (IP3)
  4. Calcium (Ca2+)

Question 4

Describe how cAMP is formed and act as second messenger

Answer 4

• extracellular signal molecule binds to Gprotein linked receptor
  —> activates adenylyl cyclase and increase in cAMP concentration.
  —> increase leads to activation of PKA release into cytosol

Question 5

Describe how nuclear receptors (intracellular receptors) work.

Answer 5

• lipophilic signals are carried by protein to blood to be dissociated before entering target cell
• small hydrophobic signal molecules diffuse across the plasma membrane target cells
  —> bind to transcription intracellular receptors
  —> they bind to their respective intracellular receptor proteins, altering the ability of proteins to control transcription of specific genes.

Question 6

What is a G - Protein Coupled receptor?

Answer 6

• also called metabotropic receptors when referencing neurotransmitters
• an integral membrane protein w/ a single polypeptide chain passing in and out of plasma
• binds to particular type of G proteins
• mediate most responses to signals from external world and other cells
  —> hormones
  —> neurotransmitters
  —> local mediators

Question 7

What is a G protein?

Answer 7

• contain 3 different types of subunits ( alpha, beta, and gamma )
• bind directly to cytoplasmic domain
• molecular on off switches
• signaling is like a molecular relay race

Question 8

What is the process for G proteins?

Answer 8

1. alpha subunit is GTPase and has GDP bound to inactive site
2. G-alpha subunit exchanges GDP for GTP
3. Activation dissociates beta/gamma complex from alpha
4. Both GTP bound alpha and beta/gamma complex interact w/ targets
5. GTPase hydrolyzes GTP to GDP and becomes inactive again.