chapter 5 g protein-coupled receptors. you must know the three stages of cell signaling. the...

Chapter 5G Protein-Coupled Receptors

You must know

• The three stages of cell signaling.

• The function of G protein-coupled receptors. (This is a type of cell signaling.)

The Three Stages of Cell Signaling

• Cells receiving signals undergo three processes– Reception– Transduction– Response

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Figure 5.20-1

EXTRACELLULARFLUID Plasma membrane

Reception

Receptor

SignalingMolecule A.K.A. ligand

CYTOPLASM

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The ligand is specific to the receptor

Plasma membrane protein

Figure 5.20-2

EXTRACELLULARFLUID

CYTOPLASM

Plasma membrane

Reception Transduction

Relay molecules

Receptor

Signalingmolecule

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EXTRACELLULARFLUID

CYTOPLASM

Plasma membrane

ResponseReception Transduction

Relay molecules

Activation

Receptor

Signalingmolecule

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The response may be almost any imaginable cellular activity…

Receptors in the Plasma Membrane

• There are two main types of membrane receptors– G protein-coupled receptors– Ligand-gated ion channels

Plasma membrane

Receptor

CYTOPLASM

Plasma membrane protein

hydrophilicsignaling molecule

Importance of G protein-coupled receptors

• Nearly 1,000 different types that we know of.

• Nearly 60% of all medicines influence G protein-coupled receptors.

• Involved in:– Embryonic development– Senses of smell– Sense of taste– Maintaining homeostasis!

• Ex. Cholera, whooping cough, and botulism are caused by toxins that interfere with G protein-coupled receptors.

• Video: https://www.youtube.com/watch?v=V_0EcUr_txk

1. The G protein is “off” because it is bound to GDP. (GDP is similar to ADP)

Signal (ligand)

Receptor

G protein in “off” conformation

2. The ligand binds to the receptor.

Signal (ligand)

Receptor

G protein in “off” conformation

3. The ligand binding to the receptor cause the receptor to change shape.

Signal (ligand)

Receptor

G protein in “off” conformation

4. The receptor changing shape is a switch that activates its G protein. The G protein releases the GDP molecule that kept it in an inactive state and binds to GTP instead.

Signal (ligand)

5. When GTP is attached, the G protein becomes activated and splits into two parts.

Signal (ligand)

Receptor

G protein in “off” conformation

6. One part of the “split” G protein activates a nearby enzyme that is embedded in the plasma membrane. The activated enzyme catalyzes the production of second messengers. The second messengers are small signaling molecules that diffuse rapidly to spread the signal throughout the cell and elicit a cellular response.

Signal (ligand)

Receptor

G protein in “off” conformation

Cellular response

Activatedenzyme

SecondMessengers