Lecture 18- Metabotropic Receptors

* 7 Transmembrane segments
* Not in subunits
* One protein
* Conserved

Name three key characteristics of metabotropic receptors

* Lipids
* Ca2+ ions
* Light (photons)
* Odorant molecules
* Peptides and proteins
* small molecule transmitters

Name the different types of metabotropic receptors

1. Liver homogenate is added to a cell vial
2. Epinephrine is added
3. When epinephrine was added, increased liver phosphorylase activity

Explain the first experiment for the discovery of second messengers

1. Liver homogenate is added to a cell vial
2. The cell is placed through a centrifuge to spin down to remove membranes
3. Epinephrine is added
4. No change in liver phosphorylase activity without membranes present

Showed: membrane is necessary for kinase activity

Explain the second experiment for the discovery of second messengers and state what it showed.

Part 1:


1. Liver homogenate is added to a cell vial
2. Epinephrine is added to cell vial, which increases liver homogenate activity
3. Membrane is spun down to isolate epinephrine-treated cytoplasm (containing cAMP)

Part 2:


1. Spin down to remove membranes, add epinephrine (no change in liver phosphorylase activity without membranes present.
2. Add epinephrine treated cytoplasm containing cAMP to cytoplasm that includes liver phosphorylase


1. Increase liver phosphorylase activity

Explain the third experiment for the discovery of second messengers

1. External signal (ligand, first messenger) binds to receptor
2. Receptor includes transducer
3. Transducer incudes primary effector
4. Primary effectors turns on second messenger
5. Second messenger turns on secondary effector
6. Secondary effector produces cellular response

Explain the pathway from ligand to secondary effector

1. Ga is bound to GDP- considered inactive
2. Ga is bound to GyGb

What is considered the “resting” state for G-Proteins?

always bound to lipids that are embedded in the membrane- helps to keep associated with the membrane

What are GyGb bound to and why?

1. A ligand binds to the receptor
2. Receptor changes confirmation, Ga has a lower affinity for GDP and a higher affinity for GTP
3. GDP to GTP exchange
4. When ligand is bound, breaks into two dimers: GyGb and Ga+GTP, which acts as a transducer

Explain the activation of G-Proteins

membrane

Activated G-Proteins remain ____________ associated

1. Ga hydrolyzes GTP into GDP, phosphate group is removed
2. Ga binds to GyGb as Ga has a high affinity
3. Re-association with receptor

Explain the inactivation of G-Proteins

1. Instrinsic GTPase activity of Ga subunit
2. Interaction with effector
3. Regulation of G-Protein signaling proteins

Name the three types of termination of metabotropic signaling

1. Ga hydrolyzes GTP to GDP, removes phosphate group
2. Ga binds to GyGb as Ga has a high affinity
3. Re-association with receptor

Explain intrinsic GTPase activity of Ga subunit for termination of metabotropic signaling

Effector will speed up the rate of hydrolysis by a subunit allowing Ga to bind faster to GDP

Explain interaction with effector for termination of metabotropic signaling

terminate the action of Ga subunit

* are not effectors

Explain regulation of G-Protein signaling proteins for termination of metabotropic signaling

1. Remove GTP from intracellular solution
2. Use GTP-y-S
3. Use GDP-B-S

Name the three experiments to demonstrate the role of GTP

* Use whole cell recording
* wash out all GTP
* Place in NT
* Nothing happens

Explain the experiment that removes GTP from intracellular solution to demonstrate role of GTP

* Non-hydrolysable from of GTP
* Permanately active

Explain the experiment that uses GTP-y-S to demonstrate the role of GTP

* GTP cannot compete with GDP-B-S

Explain the experiment that uses GDP-B-S to demonstrate role of GTP

Prevents translation of mRNA to protein

(Which G-Protein is related to which receptor)

What is the goal/role of an antisense oligonucleotide?

spatially segregate

Macromolecular complexes can_________________ signaling cascades