Chapter 11 notes

Cell Communication

The Cellular Internet

Trillions of cells in a multicellular organism must communicate together to enable growth, survival, and reproduction

The same cell-signaling mechanisms tend to show up again and again

Concept 11.1

Yeast cells use cell signaling to identify mates- two sexes, type a and type a- cells secrete a chemical signal that binds to receptors on the opposite cell- causes the two cells to grow toward each other so they can fuse and mate

Concept 11.1

Signal transduction pathway: process by which a signal on a cell’s surface is converted into a specific cellular response

Concept 11.1Receptor

factor

a factor

a

a

Exchangeof matingfactors

Yeast cell,mating type a

Yeast cell,mating type

Mating

New a/cell

a/

1

2

3

Concept 11.1

Some cells communicate through direct contact- use of cell junctions- animal cells use membrane-bound cell surface molecules

Concept 11.1Plasma membranes

Gap junctionsbetween animal cells

(a) Cell junctions

Plasmodesmatabetween plant cells

(b) Cell-cell recognition

Concept 11.1

Some molecules only travel a short distance- local regulators (ex. growth factors)

Synaptic signaling is found in the nervous system- electrical signal triggers the release of neurotransmitters across a synapse

Concept 11.1

Hormones are used for long-distance signaling- specialized cells release hormones into the circulatory system to travel to other parts of the body

Concept 11.1

Local signaling

Target cell

Secretingcell

Secretoryvesicle

Local regulatordiffuses throughextracellular fluid

(a) Paracrine signaling (b) Synaptic signaling

Target cellis stimulated

Neurotransmitter diffuses across synapse

Electrical signalalong nerve celltriggers release ofneurotransmitter

Long-distance signaling

Endocrine cell Bloodvessel

Hormone travelsin bloodstreamto target cells

Targetcell

(c) Hormonal signaling

Concept 11.1

The receiving end of a signal can be organized into three stages:

Reception- a chemical signal is bound to a receptor protein at the cell’s surface

Transduction- converts the signal to a form that can produce a cellular response

Concept 11.1

Response- any cellular activity that the cell is directed to accomplish

Concept 11.1

Concept 11.1

Concept 11.1

Concept 11.2

Reception - the receptor protein on a target

cell allows the cell to “hear” the message from a signal- the signal is complementary in shape and attaches to the protein- the receptor protein changes shape, and thus is activated

Concept 11.2

Receptors can be intracellular or plasma membrane bound

To reach the intracellular receptors, messengers must be able to pass through the plasma membrane (either small or hydrophobic)- ex. steroid hormones or NO (nitric oxide)

Concept 11.2

Most water soluble molecules are going to bind to plasma membrane receptors- receptor transmits information from the outside environment to the inside of the cell

Concept 11.2

G protein-coupledreceptor

Plasmamembrane

EnzymeG protein(inactive)

GDP

CYTOPLASM

Activatedenzyme

GTP

Cellular response

GDP

P i

Activatedreceptor

GDP GTP

Signaling moleculeInactiveenzyme

1 2

3 4

Concept 11.3

Transduction- usually a multi-step process- benefit in that it greatly amplifies a signal

Protein kinase: an enzyme that transfers phosphate groups from ATP to a protein

Concept 11.3Signaling molecule

Receptor Activated relay

molecule

Inactiveprotein kinase

1Activeproteinkinase

1Inactiveprotein kinase

2

ATPADP Active

proteinkinase

2

P

PPP

Inactiveprotein kinase

3

ATPADP Active

proteinkinase

3

P

P PPi

ATPADP P

ActiveproteinPPP i

Inactiveprotein

Cellularresponse

Phosphorylation

cascade

i

Concept 11.3

Many signaling pathways also involve small, nonprotein molecules called second messengers- ex. cyclic AMP (cAMP) carries a signal initiated by epinephrine from the plasma membrane of a liver cell into the cell’s interior

Concept 11.3

- the binding of epinephrine to a liver cell activates adenlyl cyclase, which in turn can synthesize many molecules of cAMP

Concept 11.3

First messenger

G proteinAdenylylcyclase

GTP

ATPcAMP Second

messenger

Proteinkinase A

G protein-coupledreceptor

Cellular responses

Concept 11.4

ResponseIn the liver cells, the final step

activates the enzyme that catalyzes the breakdown of glycogen into glucose

Many other signaling pathways regulate the synthesis of an enzyme by turning genes on and off

Concept 11.4

Signal Amplification- at each step in the cascade, the number of activated products is much greater than the preceding steps- b/c the proteins persist in an active form long enough to process numerous molecules

Concept 11.4

Specificity of Cell Signaling- ex. heart cells vs. liver cells

- respond to some signals but ignore others

- different responses to the same signal (ex. epinephrine)