Cell Communication

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3

Concept 11.2: Reception: A signal molecule binds to a receptor protein, causing it to change shape

The binding between a signal molecule (ligand) and receptor is highly specific

A shape change in a receptor is often the initial transduction of the signal

Most signal receptors are plasma membrane proteins

Slide 19

Receptors in the Plasma Membrane

Most water-soluble signal molecules bind to specific sites on receptor proteins in the plasma membrane

There are three main types of membrane receptors:

G protein-coupled receptors

Receptor tyrosine kinases

Ion channel receptors

Slide 20

A G protein-coupled receptor is a plasma membrane receptor that works with the help of a G protein

The G protein acts as an on/off switch: If GDP is bound to the G protein, the G protein is inactive

Slide 21

Fig. 11-7a

Signaling-molecule binding site

Segment that

interacts with

G proteins

G protein-coupled receptor

Slide 22

Fig. 11-7b

G protein-coupled

receptor

Plasma

membrane

Enzyme

G protein

(inactive)

GDP

CYTOPLASM

Activated

enzyme

GTP

Cellular response

GDP

P

i

Activated

receptor

GDP

GTP

Signaling molecule

Inactive

enzyme

1

2

3

4

Slide 23

Receptor tyrosine kinases are membrane receptors that attach phosphates to tyrosines

A receptor tyrosine kinase can trigger multiple signal transduction pathways at once

Slide 24

Fig. 11-7c

Signaling

molecule (ligand)

Ligand-binding site

 Helix

Tyrosines

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Receptor tyrosine

kinase proteins

CYTOPLASM

Signaling

molecule

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Dimer

Activated relay

proteins

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

P

P

P

P

P

P

Cellular

response 1

Cellular

response 2

Inactive

relay proteins

Activated tyrosine

kinase regions

Fully activated receptor

tyrosine kinase

6

6 ADP

ATP

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

P

P

P

P

P

P

1

2

3

4

Slide 25

A ligand-gated ion channel receptor acts as a gate when the receptor changes shape