ap biology i think she meant a different kind of cellular communication… chapter 11 cellular...

AP Biology

I think she meanta different kind of

cellular communication…

Chapter 11

Cellular Communication

Don’t you get it? It’s what I meant to say, not

what I really said!…

AP Biology

External signals are converted to responses within the cell

© 2011 Pearson Education, Inc.

Exchange of mating

factors

Receptor

factor

factor

Yeast cell,mating type a

Yeast cell,mating type

Mating

New a/ cell

1

2

3

a

a

a/

Yeast has two mating types,

a and Cells locate each other via

secreted factors

Signal Transduction Pathway

series of steps that convert a

signal on a cell’s surface into

a specific cellular response.

a factor

AP Biology

Pathway similarities suggest ancestral signaling molecules evolved in prokaryotes and later modified in eukaryotes.

Signal molecule concentration allows bacteria to sense population density.


Common trait, common ancestry…

AP Biology

Individualrod-shaped

cells

Spore-formingstructure

(fruiting body)

Aggregation in progress

Fruiting bodies

1

2

3

0.5 mm

2.5 mm

Figure 11.3

AP Biology

Long-Distance and Local Signaling Cells in a multicellular organism

communicate by chemical messengers. Animal and plant cells use

cell junctions directly

connect cytoplasm of adjacent

cells

And

Local signaling communication by direct contact,

or by cell-cell recognition


Plasma membranes

Gap junctionsbetween animal cells

Plasmodesmatabetween plant cells

(a) Cell junctions

(b) Cell-cell recognition

AP Biology

Long-Distance Signaling

plants and animals use chemicals called hormones

The ability of a cell to respond to a signal depends on presence of the receptor specific to that signal


Long-distance signaling

Endocrine cell Bloodvessel

Hormone travelsin bloodstream.

Target cellspecifically

binds hormone.

(c) Endocrine (hormonal) signaling

AP Biology

Local Signaling messenger molecules that travel only short distances


Target cell

Secretingcell

Secretoryvesicle

Local regulatordiffuses through

extracellular fluid.

(a) Paracrine signaling (b) Synaptic signaling

Electrical signalalong nerve cell

triggers release ofneurotransmitter.

Neurotransmitter diffuses across

synapse.

Target cellis stimulated.

AP Biology

Three Stages of Cell Signaling:

Earl W. Sutherland discovered how the hormone epinephrine acts on cells

Sutherland suggested that cells receiving signals went through three processes

Reception Transduction Response


AP Biology© 2011 Pearson Education, Inc.

Animation: Overview of Cell Signaling Right-click slide / select “Play”

AP Biology

Figure 11.6-1

Plasma membrane

EXTRACELLULARFLUID

CYTOPLASM

Reception

Receptor

Signalingmolecule

1

Plasma membrane

EXTRACELLULARFLUID

CYTOPLASM

Reception Transduction

Receptor

Signalingmolecule

Relay molecules in a signal transductionpathway

21

Plasma membrane

EXTRACELLULARFLUID

CYTOPLASM

Reception Transduction Response

Receptor

Signalingmolecule

Activationof cellularresponse

Relay molecules in a signal transductionpathway

321

Reception: signaling molecule binds to receptor protein, causing conformation change. 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

AP Biology

Types of Receptors in the Plasma Membrane

Water-soluble signal molecules bind to specific sites on receptor proteins that span the plasma membrane

There are three main types of membrane receptors

G protein-coupled receptorsReceptor tyrosine kinasesIon channel receptors



G protein-coupled receptors (GPCRs)

• Largest family of cell-surface receptors.

• Works with the help of a G protein (Guanine nucleotide-

binding proteins) - acts as an on/off switch.

“off” when bound to GDP (Guanine diphosphate)

“on” when bound to GTP (Guanine triphosphate)

You know what turns me on!

…and off!

AP Biology

Figure 11.7a

G protein-coupled receptor

Signaling molecule binding site

Segment thatinteracts with

G proteins

AP Biology

Figure 11.7b

G protein-coupledreceptor

21

3 4

Plasmamembrane

G protein(inactive)

CYTOPLASMEnzyme

Activatedreceptor

Signalingmolecule

Inactiveenzyme

Activatedenzyme

Cellular response

GDPGTP

GDPGTP

GTP

P i

GDP

GDP

http://www.youtube.com/watch?

v=4dUJ5GNpfrA&feature=endscreen&NR=1

AP Biology

Receptor tyrosine kinases (RTKs) receptors that attach phosphates to tyrosines

A receptor tyrosine kinase can trigger

multiple signal transduction pathways at once Abnormal functioning of RTKs is associated

with many types of cancers


AP Biology

Figure 11.7c

Signalingmolecule (ligand)

21

3 4

Ligand-binding site

helix in themembrane

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 tyrosinekinase regions

(unphosphorylateddimer)

Fully activatedreceptor tyrosine

kinase(phosphorylated

dimer)

Activated relayproteins

Cellularresponse 1

Cellularresponse 2

Inactiverelay proteins

6 ATP 6 ADP

AP Biology

Ligand-gated ion channel receptors acts as gates when the receptors change shape.

When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor


AP Biology

Figure 11.7d

Signalingmolecule (ligand)

21 3

Gate closed Ions

Ligand-gatedion channel receptor

Plasmamembrane

Gate open

Cellularresponse

Gate closed

AP Biology

Intracellular Receptors Intracellular receptor proteins are found in

the cytosol or nucleus of target cells

Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors

Examples of hydrophobic messengers are the steroid and thyroid hormones of animals

An activated hormone-receptor complex can act as a transcription factor, turning on specific genes


AP Biology

Figure 11.9-1

Hormone(testosterone)

Receptorprotein

Plasmamembrane

DNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID


Receptorprotein

Plasmamembrane

Hormone-receptorcomplex

DNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID


Receptorprotein

Plasmamembrane


DNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID


Receptorprotein

Plasmamembrane


DNA

mRNA

NUCLEUS

CYTOPLASM

EXTRACELLULARFLUID


Receptorprotein

Plasmamembrane

EXTRACELLULARFLUID


DNA

mRNA

NUCLEUS

CYTOPLASM

New protein

I like this Testosterone

stuff!

AP Biology

Figure 11.9-5


Receptorprotein

Plasmamembrane

EXTRACELLULARFLUID


DNA

mRNA

NUCLEUS

CYTOPLASM

New protein

1.

2.

3.

4.

5.

6.

AP Biology

Transduction:

Cascades of molecular interactions relay signals from receptors to target molecules in the cell Signal transduction usually involves multiple

steps Can amplify a signal: A few molecules can

produce a large cellular response provide more opportunities for coordination

and regulation of the cellular response


AP Biology

Signal Transduction Pathways

The molecules that relay a signal from receptor to response are mostly proteins.

Like falling dominoes, the receptor activates another protein, which activates another, and so on, until the protein producing the response is activated.

At each step, the signal is transduced into a different form, usually a conformational change in a protein.


AP Biology

Protein Phosphorylation and Dephosphorylation

In many pathways, the signal is transmitted by a cascade of protein phosphorylations.

Protein kinases transfer phosphates from ATP to protein, a process called phosphorylation.


AP Biology

Protein phosphatases remove the phosphates from proteins, a process called dephosphorylation.

This phosphorylation and dephosphorylation system acts as a molecular switch, turning activities on and off or up or down, as required.


AP Biology

Activated relaymolecule

Phosphorylation cascade

Inactiveprotein kinase

1 Activeprotein kinase

1

Activeprotein kinase

2

Activeprotein kinase

3


2


3

Inactiveprotein

Activeprotein

ATPADP

ATPADP

ATPADP

PP

PP

PP

P

P

P i

P i

P i

P

Figure 11.10aSignaling molecule

Cellularresponse

AP Biology

Small Molecules and Ions as Second Messengers

“First messenger” - extracellular signal

molecule (ligand) binds to the receptor. Second messengers are small, nonprotein,

water-soluble molecules or ions that spread throughout a cell by diffusion.

ex. - Cyclic AMP and calcium ions Second messengers participate in pathways

initiated by GPCRs and RTKs


AP Biology

Cyclic AMP• Cyclic AMP (cAMP) - widely used second

messenger.

• Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal.


Adenylyl cyclase Phosphodiesterase

Pyrophosphate

AMP

H2O

ATP

P iP

cAMP

AP Biology

Many signal molecules trigger formation of cAMP.

Components of cAMP pathways: a) G proteins

b) G protein-coupled receptors

c) protein kinases

cAMP usually activates protein kinase A, which phosphorylates various other proteins.

Further regulation of cell metabolism is provided by G-protein systems that inhibit adenylyl cyclase (which shuts down cAMP production).


AP Biology

Figure 11.12

G protein

First messenger(signaling molecule

such as epinephrine)


Adenylylcyclase

Second messenger

Cellular responses

Proteinkinase A

GTP

ATP

cAMP

AP Biology

Calcium Ions and Inositol Triphosphate (IP3)

Calcium ions (Ca2+) act as a second messenger in many pathways

Calcium is an important second messenger because cells can regulate its concentration


Mitochondrion

EXTRACELLULARFLUID

Plasmamembrane

Ca2

pump

Nucleus

CYTOSOL

Ca2

pump

Ca2

pump

Endoplasmicreticulum

(ER)

ATP

ATP

Low [Ca2 ]High [Ca2 ]Key

AP Biology

Figure 11.13

Mitochondrion

EXTRACELLULARFLUID

Plasmamembrane

Ca2

pump

Nucleus

CYTOSOL

Ca2

pump

Ca2

pump

Endoplasmicreticulum

(ER)

ATP

ATP

Low [Ca2 ]High [Ca2 ]Key

AP Biology

A signal relayed by a signal transduction pathway may trigger an increase in calcium in the cytosol

Pathways leading to the release of calcium involve inositol triphosphate (IP3) and diacylglycerol (DAG) as additional second messengers



Animation: Signal Transduction Pathways Right-click slide / select “Play”

AP Biology

Figure 11.14-3

G protein

EXTRA-CELLULAR

FLUID

Signaling molecule(first messenger)


Phospholipase C

DAG

PIP2

IP3

(second messenger)

IP3-gatedcalcium channel

Endoplasmicreticulum (ER)

CYTOSOL

Variousproteinsactivated

Cellularresponses

Ca2

(secondmessenger)

Ca2

GTP

AP Biology

Nuclear and Cytoplasmic Responses

Signal transduction pathway leads to regulation of one or more cellular activities

Response may occur in the cytoplasm or in the nucleus

Many signaling pathways regulate the synthesis of enzymes or other proteins, usually by turning genes on or off in the nucleus

The final activated molecule in the signaling pathway may function as a transcription factor.


AP Biology

Figure 11.15

Growth factor

Receptor

Reception

Transduction

CYTOPLASM

Response

Inactivetranscription

factor

Activetranscription

factor

DNA

NUCLEUS mRNA

Gene

Phosphorylationcascade

P

AP Biology

Other pathways regulate the activity of enzymes rather than their synthesis


Signaling pathways can also affect the overall behavior of a cell, for example, changes in cell shape

AP Biology

Fine-Tuning of the Response

There are four aspects of fine-tuning to consider

Amplification of the signal Specificity of the response Overall efficiency of response, enhanced

by scaffolding proteins Termination of the signal


AP Biology

Signal Amplification

Enzyme cascades amplify the cell’s response.

At each step, the number of activated products is much greater than in the preceding step.


AP Biology

The Specificity of Cell Signaling and Coordination of the Response

Different kinds of cells have different collections of proteins

These different proteins allow cells to detect and respond to different signals

Even the same signal can have different effects in cells with different proteins and pathways

Pathway branching and “cross-talk” further help the cell coordinate incoming signals


AP Biology

Figure 11.18

Signalingmolecule

Receptor

Relay molecules

Response 1

Cell A. Pathway leadsto a single response.

Response 2 Response 3 Response 4 Response 5

Activationor inhibition

Cell B. Pathway branches,leading to two responses.

Cell C. Cross-talk occursbetween two pathways.

Cell D. Different receptorleads to a different

response.

AP Biology

Signaling Efficiency: Scaffolding Proteins and

Signaling Complexes Scaffolding proteins are large relay proteins

to which other relay proteins are attached Increase the signal transduction efficiency

by grouping together proteins involved in the same pathway

May also help activate some of the relay proteins


AP Biology

Figure 11.19

Signalingmolecule

Receptor

Plasmamembrane

Scaffoldingprotein

Threedifferentproteinkinases

AP Biology

Termination of the Signal

Inactivation mechanisms are an essential aspect of cell signaling.

If ligand concentration falls, fewer receptors will be bound.

Unbound receptors revert to an inactive state.


AP Biology

Apoptosis integrates multiple cell-signaling pathways

Apoptosis is programmed or controlled cell suicide

Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells

Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells


AP Biology

Apoptotic Pathways and the Signals That Trigger Them

Caspases -the main proteases (enzymes that cut up proteins) that carry out apoptosis

Apoptosis can be triggered by An extracellular death-signaling ligand DNA damage in the nucleus Protein misfolding in the endoplasmic

reticulum


AP Biology

Apoptosis evolved early in animal evolution and is essential for the development and maintenance of all animals

Apoptosis may be involved in some diseases (for example, Parkinson’s and Alzheimer’s); interference with apoptosis may contribute to some cancers


Interdigital tissueCells undergoing

apoptosisSpace between

digits1 mm

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