Cell CommunicationAP BIO

Hey! • As mentioned in the email: College

Board is only testing on units 1-6. This ppt covers more than half of unit 4. This ppt stops at “Feedback”. On Wednesday I will release the PPT for the Cell Cycle and errors in the cell cycle.

• Read over the ppt carefully, and complete POGIL on the website.

• Also: go to USA testprep. • Join class: Mr. Smith (not Marcel

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Methods used by Cells to Communicate• Cell-Cell communication• Cell Signaling using chemical messengers

1. Local signaling over short distances• Cell-Cell Recognition• Local regulators

– Paracrine (growth factors)– Synaptic (neurotransmitters)

2. Long distance signaling• Hormones

Cell-Cell Communication• Animal and plant cells– Have cell junctions that directly connect the cytoplasm of

adjacent cellsPlasma membranes

Plasmodesmatabetween plant cells

Gap junctionsbetween animal cells

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

Gap junctionsbetween animal cells

Cell-Cell Communication

• Animal cells use gap junctions to send signals• Cells must be in direct contact• Protein channels connecting two adjoining cells

Figure 11.3(b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces.

Local Signaling: Cell-Cell Recognition• In local signaling, animal cells may communicate via direct contact

• Membrane bound cell surface molecules• Glycoproteins• Glycolipids

Local Signaling: Local Regulators• In other cases, animal cells– Communicate using local regulators – Only work over a short distance

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

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

Local regulator diffuses through extracellular fluid

Target cell

Secretoryvesicle

Electrical signalalong nerve celltriggers release ofneurotransmitter

Neurotransmitterdiffuses across

synapse

Target cellis stimulated

Local signaling

Long-distance Signaling: Hormones• 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

Figure 11.4 C

Long-Distance Signaling§ Nervous System in Animals

u Electrical signals through neurons§ Endocrine System in Animals

u Uses hormones to transmit messages over long distances

§ Plants also use hormonesu Some transported through vascular

systemu Others are released into the air

The Three Stages of Cell Signaling• Cells receiving signals through three processes

• Reception• Transduction• Response

• Called Signal transduction pathways• Convert signals on a cell’s surface into cellular responses• Are similar in microbes and mammals, suggesting an early

origin

EXTRACELLULARFLUID

Receptor

Signal molecule

Relay molecules in a signal transduction pathway

Plasma membraneCYTOPLASM

Activationof cellularresponse

Figure 11.5

Overview of cell signaling

Reception1 Transduction2 Response3

Reception1

EXTRACELLULARFLUID

Receptor

Signalingmolecule

Plasma membraneCYTOPLASM

1

Three Stages of Cell Signaling

• Signaling molecule binds to the receptor protein• This is called a ligand• The ligand will start the reaction inside the cell

The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!)

Three Stages of Cell Signaling

Reception1

EXTRACELLULARFLUID

Receptor

Signalingmolecule

Plasma membraneCYTOPLASM

1

Relay molecules in a signal transduction pathway

Transduction2

§ The signal is converted into a form that can produce a cellular response

2ndMessenger!

EXTRACELLULARFLUID

Plasma membraneCYTOPLASM

Receptor

Signalingmolecule

Relay molecules in a signal transduction pathway

Activationof cellularresponse

Reception Transduction Response1 2 3

Three Stages of Cell Signaling

§ The transduced signal triggers a cellular response

Can be catalysis, activation of a gene, triggering apoptosis, almost anything!

1. Reception• A signal molecule, a ligand, binds to a receptor

protein in a lock and key fashion, causing the receptor to change shape.

Most receptor proteins are in the cell

membrane but some are inside the cell.

The G-protein is a common membrane

receptor.

Signalingmolecule(ligand)

Gateclosed Ions

Ligand-gatedion channel receptor

Plasmamembrane

Gate open

Cellularresponse

Gate closed

1

2

3

Ion Channel Receptors• Very important in the

nervous system• Signal triggers the

opening of an ion channel• depolarization• Triggered by

neurotransmitters

2. Transduction• Transduction: Sends signals from receptors to target

molecules in the cell• Multistep pathways– Can amplify a signal – Provide more opportunities for coordination and regulation

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

*Remember – conformational change means the shape changes.

Fig. 11-9

Signaling molecule

ReceptorActivated relaymolecule

Inactiveprotein kinase

1 Activeproteinkinase

1

Inactiveprotein kinase

2ATP

ADP Activeproteinkinase

2

P

PPP

Inactiveprotein kinase

3ATP

ADP Activeproteinkinase

3

P

PPP

i

ATPADP P

ActiveproteinPP

Pi

Inactiveprotein

Cellularresponse

Phosphorylation cascadei

Transduction:A Phosphorylation

Cascade

3. Response• Many possible outcomes• This example shows a

transcription response

• Remember – transcription is the process of converting DNA into RNA

• If DNA is ATT • RNA will be UAA

Growth factor

Receptor

Phosphorylationcascade

Reception

Transduction

Activetranscriptionfactor Response

P

Inactivetranscriptionfactor

CYTOPLASM

DNA

NUCLEUSmRNA

Gene

Response- cell signaling leads to regulation of transcription (turn genes on or off) or cytoplasmic

activities.

Long-distance SignalingIntracellular signaling includes hormones that are

hydrophobic and can cross the cell membrane.

Once inside the cell, the hormone attaches to a protein that takes it into the nucleus where transcription can be

stimulated.

Testosterone acts as a transcription factor.

Termination of the Signal• Signal response is terminated quickly– By the reversal of ligand binding

The three stage of cellular signaling: Reception, Transduction, and Response.

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