Chapter 11:Cell Communication

Sig

nal-T

rans

duct

ion

Em

phas

is This chapter’s emphasis is on signals that are

released from one cell and allowed to freely diffuse to a second (or more) recipient cell(s)

These communications are deliberately initiated, received, and interpreted in order to increase the physiological coordination of the cells in multicellular organisms

We will consider in particular those events that follow the reception of a chemical signal

We will not dwell on the purpose of the signal We also will not dwell on why and how a

given cell releases a given signal

Sig

nalin

g w

ith D

irect

Con

tact

Local Signaling w/o Direct Contacte.g., interferon release by viral-infected cells

Long

-Dis

tanc

e S

igna

ling

Long

-Dis

tanc

e D

iffus

ion Note how specificity is determined by

presence/absence of receptor protein

Sig

nalli

ng, F

ree-

Livi

ng C

ells

Cel

l-Cel

l Che

mic

al S

igna

ling Three general categories of chemical

signaling:• Cytoplasmic connections between cells• Cell-to-cell contact-mediated signaling• Free diffusion between cells

• Distant cells (hormones)• Adjacent cells (within interstitial space)

All of latter involves the physical movement of ligands

• That is, ligand reception by a protein• Note that reception means molecule-to-

molecule contact

Liga

nds

e.g., steroid hormonese.g., nitric oxide

e.g., epinephrinee.g., insulin

Nothing to memorize on

this page

Signal Transduction

In this case the receptor protein is a membrane proteinLigan

d

Often turning on or off enzyme activity

Thr

ee S

tage

s 2a. Transduction

2b. Transduction

2c. Transduction

2d. Transduction

1. Reception

3. Response

Responses usually involve increasing or decreasing some protein’s function

Thr

ee S

tage

s

2a. Transduction

2b. Transduction

1. Reception

3. Response

Intr

acel

lula

r R

ecep

tor

Rap

idity

of R

espo

nse Slower

response if requiring protein

synthesis

G-P

rote

in-L

inke

d R

ecep

tor

G proteins bind GTP

G-Protein-Linked ReceptorThe more ligand binding, the greater the cellular response

Note lability of all signals

Pro

tein

Kin

ase

& P

hosp

hata

seP r o te in O H + A T P P r o te in O P

O

O

O

+ A D P

P i H 2 O

P r o te in K in a s e

P r o te in P h o s p h a t a s e

Like signal lability,

reversibility of phosphorylatio

n makes signaling reversible

Therefore, responses

tend to continue (or expand) only

so long as signaling continues

This reversibility contributes

to the dynamic nature of

cells

Tyrosine Kinase Receptor

Receptor Tyrosine KinaseNote steps involved:1. Ligand Reception2. Receptor Dimerization3. Catalysis (Phosphorylization)4. Subsequent Protein Activation5. Further Transduction6. Response

Ion-

Cha

nnel

Rec

epto

r

Reversibility is assured by pumping ions

back out again (using

separate protein)

Pho

spho

ryla

tion

Cas

cade

Cyclic AMP (cAMP)

“Second” Messenger

Second messengers

are not proteins

Note reversibility

2nd

Mes

seng

er, S

.T.P

.

Ca2+

-med

iate

d S

igna

l Am

p.

Releasing Ca2+ is a means of greatly amplifying signal

Sig

nal A

mpl

ifica

tion

(Cas

cade

)

Sig

nal A

mpl

ifica

tion

(Cas

cade

)

Note how, via catalysis, one ligand molecule binding gives rise to many new intracellullar molecules

Sig

nal A

mpl

ifica

tion

(Cas

cade

)

Sig

nal-T

rans

duct

ion

Cas

cade

Seek to understand the concept, rather

than memorize the specific protein

Nuc

lear

Res

pons

e

Var

ious

Res

pons

es Note that more than one

response can result from the reception of a single ligand

Var

ious

Res

pons

es Same ligand

gives rise to different responses

(here same receptor, different relay)

Cells differ in terms of their proteins

Different proteins respond differently to the same environmental signals

The End