Cell Signaling

Figure 11.6-3

Plasma membraneEXTRACELLULAR FLUID

CYTOPLASM

Reception Transduction Response

Receptor

Signalingmolecule

Activationof cellular response

Relay molecules in a signal transductionpathway

321

Signal Transduction Pathway

1. Reception = target cell detects signal from outside; signal molecule binds to receptor protein

2. Transduction = binding of signal molecule changes receptor protein; may be single step or pathway

3. Response = transduced signal causes cellular activity

Figure 11.6-3

Plasma membraneEXTRACELLULAR FLUID

CYTOPLASM

Reception Transduction Response

Receptor

Signalingmolecule

Activationof cellular response

Relay molecules in a signal transductionpathway

321

Figure 11.2

Exchange of mating factors

Receptor α factor

a factorYeast cell,

mating type aYeast cell,

mating type α

Mating

New a/α cell

1

2

3

a

a

a/α

α

α

Advantages of the new a/α cell?

Example: Mating in Yeast

Types of Cell Signaling

Local v. Long-Distance Signaling

Local Signaling

direct contact = cell to cell recognition, cell junctions

messenger molecules = paracrine signaling, synaptic signaling, quorum sensing

Figure 11.4Plasma membranes

Gap junctions between animal cells

Plasmodesmatabetween plant cells

(a) Cell junctions

(b) Cell-cell recognition

Figure 11.5

Local signaling

Target cell

Secretingcell

Secretoryvesicle

Local regulator diffuses throughextracellular fluid.

(a) Paracrine signaling (b) Synaptic signaling

Electrical signalalong nerve celltriggers release ofneurotransmitter.

Neurotransmitter diffuses across synapse.

Target cellis stimulated.

*Growth factors* *Nervous system*

Local Signaling- Quorum Sensing

Accumulating signal molecule allows bacteria to determine density; coordinates behavior

Local v. Long-Distance Signaling (cont.)

Long-Distance Signaling

hormones = endocrine signaling

molecules travel through circulatory system to target cells; molecular structures vary

ex: insulin & glucagon (more on this later!)

Signals and Receptors

Cell-Surface Transmembrane Receptors

1. G-protein coupled receptors

2. Receptor tyrosine kinases

3. Ion channel receptors

Figure 11.7a

G protein-coupled receptor

Signaling molecule binding site

Segment thatinteracts with G proteins

G Protein-Coupled Receptor

Figure 11.7b

G protein-coupled receptor

21

3 4

Plasma membrane

G protein(inactive)

CYTOPLASM Enzyme

Activatedreceptor

Signalingmolecule

Inactive enzyme

Activatedenzyme

Cellular response

GDPGTP

GDPGTP

GTP

P i

GDP

GDP

G protein-coupled receptor

Figure 11.7c

Signaling molecule (ligand)

21

3 4

Ligand-binding site

α helix in the membrane

Tyrosines

CYTOPLASM Receptor tyrosine kinase proteins (inactive monomers)

Signalingmolecule

Dimer

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

P

P

P

P

P

P

P

P

P

P

P

P

Activated tyrosine kinase regions(unphosphorylateddimer)

Fully activatedreceptor tyrosine kinase(phosphorylateddimer)

Activated relayproteins

Cellularresponse 1

Cellularresponse 2

Inactive relay proteins

6 ATP 6 ADP

Receptor Tyrosine Kinase

Insulinreleased by pancreas; hormone

causes cells to pull glucose out of blood when blood glucose level rises too high

1. reception = liver cells receive insulin (signal) released by pancreas - enzymes/dimers are activated; phosphorylated

2. transduction = activated enzymes begin relay to proteins

3. response = liver takes in glucose and stores as glycogen

Glucagon

released by pancreas; hormone

causes glucose to be released from liver when blood glucose level gets too low

functions with a g protein receptor

Glucagon/Insulin Feedback Loop

Figure 11.7d

Signaling molecule (ligand)

21 3

Gate closed Ions

Ligand-gatedion channel receptor

Plasma membrane

Gate open

Cellularresponse

Gate closed

Ion Gated Channel Receptors

Ex. Neurotransmission

Why all the steps?! • Many steps amplify the signal (cascade)

• Well coordinated; do not affect outside cells

• Different types of cells —> Different genes expressed —> Different types of responses!

Figure 11.10

Receptor

Signaling molecule

Activated relaymolecule

Phosphorylation cascade

Inactive protein kinase

1 Active protein kinase

1

Active protein kinase

2

Active protein kinase

3

Inactive protein kinase

2

Inactive protein kinase

3

Inactive protein

Active protein

Cellularresponse

ATPADP

ATPADP

ATPADP

PP

PP

PP

P

P

P

P i

P i

P i

Figure 11.16

Reception

Transduction

Response

Binding of epinephrine to G protein-coupled receptor (1 molecule)

Inactive G protein

Active G protein (102 molecules)

Inactive adenylyl cyclaseActive adenylyl cyclase (102)

ATPCyclic AMP (104)

Inactive protein kinase AActive protein kinase A (104)

Inactive phosphorylase kinaseActive phosphorylase kinase (105)

Inactive glycogen phosphorylaseActive glycogen phosphorylase (106)

GlycogenGlucose 1-phosphate

(108 molecules)

Ex. Epinephrine

Secondary Messenger

(cAMP)

Figure 11.12

G protein

First messenger(signaling molecule such as epinephrine)

G protein-coupled receptor

Adenylylcyclase

Second messenger

Cellular responses

Proteinkinase A

GTP

ATPcAMP

Cholera

caused by Vibrio cholerae from human feces in drinking water

produce toxins that modify G protein to remain stuck in active form

high concentration of cAMP = large secretions of salt into intestines = profuse diarrhea = dehydration

Cholera Pathway

Apoptosis=programmed cell death

DNA is “chopped,” organelles are split

cell shrinks & forms lobes (blebbing)

vesicles package up blebs, then are engulfed

process often begins with signal from outside cell

Figure 11.20

2 µm

Figure 11.21

Mitochondrion

Ced-9 protein (active)inhibits Ced-4 activity

Receptor for death- signalingmolecule

Ced-4 Ced-3

Inactive proteins

(a) No death signal

Death-signalingmolecule

Ced-9 (inactive)

Cellforms blebs

Active Ced-4

Active Ced-3 Other

proteases

NucleasesActivationcascade

(b) Death signal

Anatomy of

Taste

Synaptic Signaling!

Taste Transduction

PTC Paper Taste Transduction

Tongue Anatomy

The pink bumps are fungiform papillae. - Each is made of dozens

of taste receptors - More papillae =

“Better” at tasting diff. flavors

Procedures

• Determine if you express the TAS2R38 gene • Determine if you are a super, normal, or non-

taster • Eat jolly rancher, focusing on dying the end

of the tongue. • Place a binder circle to create a counting

field • Count # of papillae

Suggestion: Photograph tongue

Super Taster= >30 fungiform papillae

Normal Tasters= 15-30 fungiform papillae

Non-Tasters= <15 fungiform papillae

Task: Does a certain level of “taster” relate to expressing the PTC tasting gene?

Collect data and decide!

Super Taster= >30 fungiform papillae

Normal Tasters= 15-30 fungiform papillae

Non-Tasters= <15 fungiform papillae