Cell Communication

How would you handle the following:

• You would like to tell your friend across the room about a party that is happening tonight, but you don’t want to disrupt your teacher or let anyone else in class know about it.– How could you get this message to them before

class is over?

This would be considered short/local distance, specific communication

EX: pass a note with your friend’s name on it

• A teacher wants to remind everyone in the class that they have a test on Friday.– What would be the most efficient way to contact

every student?

This would be considered short/local distance, broadcast communication

EX: write a reminder on the board

• You are a college counselor at a high school and you need to give an application to all the seniors who are applying for early admission. – How can you notify each of these people?

This would be considered long distance, specific communication

EX: make an announcement during an assembly, asking all the seniors applying for early admission to stay after for a quick meeting.

• You are on the yearbook committee and would like to organize a fundraising car wash event. – How could you get the word out to the

community, so that there is a good turnout?

This would be considered long distance, broadcast communication

EX: put an advertisement in the local paper

What are some ways that organisms use specific communication (long distance and

short distance)?

pheromones

soundscolors

How might cells communicate?

Evolution of Cell Signaling• Began in ancient prokaryotes & single celled

eukaryotes.• Critical in the microbial world:

– Bacteria will secrete chemicals signals to share information about nutrient availability.

• Starving cells secrete a chemical that will stimulate neighboring cells to aggregate. The cells form thick-walled spores allowing the cells to survive until the environment improves.

• Quorum sensing: allows bacterial populations to coordinate their behaviors so they can carry out activities that are only productive when performed by a given number of cells in synchrony.

Quorum Sensing: How bacteria communicate

Watch Bonnie Bassler-TEDTALK

• Animal and plant cells– Have cell junctions that directly connect the

cytoplasm of adjacent cells

Plasma membranes

Plasmodesmatabetween plant cells

Gap junctionsbetween animal cells

Figure 11.3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes.

(b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces.

• In local signaling, animal cells– May communicate via direct contact

–EX: immune system & embryonic development

Cell to Cell Communication- (no distance; passing a note)Immune system

I got the message, now I know the shape of the invader & will pass this on

Cell to Cell Communication (no distance; passing a note)

Cell to Cell Communication (short distance…on the board message)

Local regulator = neurotransmitters

Neurons

• Yeast cells– Identify their mates by cell signaling

factorReceptor

Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type.

1

Mating. Binding of the factors to     receptors induces changes      in the cells that     lead to their     fusion.

New a/ cell. The nucleus of the fused cell includes all the genes from the a and a cells.

2

3

factorYeast cell,mating type a

Yeast cell,mating type

a/

a

a

Figure 11.2

• In other cases, animal cells– Communicate using local regulators

(a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.

(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.

Local regulator diffuses through extracellular fluid

Target cell

Secretoryvesicle

Electrical signalalong nerve celltriggers release ofneurotransmitter

Neurotransmitter diffuses across

synapse

Target cellis stimulated

Local signaling

Growth factors Neurotransmitters

Cell to Cell Communication (long distance; hit a lot of cells…advertisement in local paper)

Message gets sent to a lot of different cells. Some will act on it and some won’t.

The ones that do act may not all act in the same way.

• In long-distance signaling– Both plants and animals use hormones

Hormone travelsin bloodstreamto target cells

(c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells.

Long-distance signaling

Bloodvessel

Targetcell

Endocrine cell

Hormonal signaling AKA: endocrine signaling

Plant hormones

• Sometimes travel through vessels but more often travel through the air as gas (ethylene).

Paracrine signaling

Synaptic signaling

Hormonal signaling

What are theses types of signals? Are they short/local or long distance? Are they specific

or general?

Short/local & general Short/local and specific

Long distance and general or specific

The Stages of Cell Signaling: A Preview• Earl W. Sutherland

– Established that epinephrine causes glycogen breakdown without passing through the membrane.

– Discovered how the hormone epinephrine acts on cells

•Sutherland suggested that cells receiving signals went through three processes

–Reception–Transduction–Response

Reception- target cells detection of a signaling molecule (ligand) that binds to a receptor protein, causing it to change shape

Transduction-several steps where each molecule brings about a change in the next molecule

Response occurs with the last molecule in the transduction pathway & triggers the cell’s response.

ReceptorsAre the binding sites for the initial signal and is responsible for transmitting the signaling into or throughout the cell.

-can be intracellular or extracellular-change shape when a ligand attaches

EX: G-protein

Like a light switch: in the “on” position, a connection is made with the energy source; in the “off” position, there is no driving energy.

• A ligand-gated Ion channel receptors

Cellularresponse

Gate open

Gate close

Ligand-gatedion channel receptor

Plasma Membrane

Signalmolecule(ligand)

Gate closed Ions

Like automatic double doors through which large crowds can flow or not flow, depending on if the doors are open or closed.

Disrupting the Communication

Dopamine is a chemical in your brain that affects your emotions, movements and your sensations

of pleasure and pain.

Drugs, such as amphetamines and cocaine, cause buildup of dopamine, which leads to drug-induced psychosis or schizophrenia.

• Signal molecules that are small or hydrophobic– And can readily cross the

plasma membrane use these receptors

Other Type of Intracellular Receptors• Intracellular receptors

– Are cytoplasmic or nuclear proteins

Like undercover cops hidden in a crowd

• Receptor tyrosine kinases (insulin uses these)

Signalmolecule

Signal-binding sitea

CYTOPLASM

Tyrosines

Signal moleculeHelix in the

Membrane

Tyr

Tyr

Tyr

Tyr

Tyr

TyrTyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

TyrTyr

Tyr

Tyr

Tyr Tyr

Tyr

TyrTyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

Tyr

DimerReceptor tyrosinekinase proteins(inactive monomers)

PP

PP

P

P Tyr

TyrTyr

Tyr

Tyr

TyrP

P

P

P

P

PCellularresponse 1

Inactiverelay proteins

Activatedrelay proteins

Cellularresponse 2

Activated tyrosine-kinase regions(unphosphorylateddimer)

Fully activated receptortyrosine-kinase(phosphorylateddimer)

6 ATP 6 ADP

Figure 11.7

Can trigger more than 1 signal transduction pathway

-coordinates many aspects of cell growth & reproduction

-abnormal tyrosine receptors (function w/o signal molecules) may contribute to some cancers.

Kinase is an enzyme that catalyzes the transfer of phosphate groups

Like a friend who brings together 2 people who otherwise don’t hang out (unless it’s with this friend); the 3 have a greater time whenever they are together.

Signal molecule

Activeproteinkinase

1

Activeproteinkinase

2

Activeproteinkinase

3

Inactiveprotein kinase

1

Inactiveprotein kinase

2

Inactiveprotein kinase

3

Inactiveprotein

Activeprotein

Cellularresponse

Receptor

P

P

P

ATPADP

ADP

ADP

ATP

ATP

PP

PP

PP

Activated relaymolecule

i

Phosphorylation cascade

P 

P

i

i

P

• A phosphorylation cascade

A relay moleculeactivates protein kinase 1.

1

2 Active protein kinase 1transfers a phosphate from ATPto an inactive molecule ofprotein kinase 2, thus activatingthis second kinase.

Active protein kinase 2then catalyzes the phos-phorylation (and activation) ofprotein kinase 3.

3

Finally, active proteinkinase 3 phosphorylates aprotein (pink) that brings about the cell’s response tothe signal.

4 Enzymes called proteinphosphatases (PP)catalyze the removal ofthe phosphate groupsfrom the proteins, making them inactiveand available for reuse.

5

SIGNAL TRANSDUCTION PATHWAYS

Like flipping the switch of a mechanical toy which goes full speed when it is turned on and is completely still when turned off.

Inactive until g-protein attaches

Converts ATP into cAMP

Has regulatory factors and catalytic factors

cAMP attaches & breaks regulatory factors away & catalytic factors become energized with the help of ATP (phosphorylation)

Activate phosphorylase to breakdown glycogen into glucose in liver cells & muscle cells.

TransductionChanging the chemical message outside the cell to a

message inside the cell.

Res

po

nse

How long does it last?• The cAMP boost does not last without another

surge of epinephrine.• If there is no epinephrine another enzyme,

phosphodiesterase, converts cAMP to AMP.

Like the trigger on a water gun, each time the trigger is pulled the reaction is immediate and temporary; cAMP is produced each time there is a cell signal stimulant (such as epinephrine) but the cAMP does not stay present long.

Microbes causing disease: Cholera: Vibrio cholerae

Toxin is a protein that modifies a G-protein so it remains stuck in active stimulating the adenylyl cyclase.

Adenylyl cyclase is continuously making cAMP

High amounts of cAMP causes intenstinal cells to secrete large amounts of salts into intestines

Water flows out by osmosis

The G-protein regulates salt & water secretion

Causing profuse diarrhea & eventually death if untreated

Bacteria colonize the lining of the small intestine & produce a toxin

Calcium Ions• Many signal molecules in animals induce responses by

increasing the cytosolic concentration of the calcium ions (Ca2+).

• Calcium is used as a second messenger– Even more often than cAMP

Like drinking caffeinated drinks, if you sip the caffeinated drink over a long period all day, it will not cause a stimulant response, but if you increase the level of caffeine in the body quickly, it causes activity to increase.

Cellular Responses can be either short-term or long-term

• Short-term:– Changes in cell shape

• EX: lymphocyte pursuit of a bacterium

– Movement of vesicles to the membrane• EX: glucose transport

• Long-term:– Activation of transcription

• EX: cause cell to start dividing, to secrete a signal for other local cells, to initiate apoptosis

“Programmed cell death”= Apoptosis

Maintaining blood glucose levels.

Feedback inhibition (negative)WHAT INSULIN DOES…

If you wanted to design a drug to maintain low blood sugar what are

some approaches?

• Design a compound– That blocks epinephrine receptor activation– That inhibits cAMP production in liver cells– To block G-protein activity in liver cells– That inhibits phosphorylase activity.

It’s time for Interactive Lessons In Biology

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