Lecture 4 Outline (Ch. 9)

I. Cell Signaling Overview

II. Signal Transduction

III. General Cell Responses

IV. Reception in Detail

V. Transduction in Detail

VI. Exam Review

Cell Signaling = Signal Transduction

Signal Transduction – receiving a signal & relaying the response

Reception Transduction Response

Receptor

Relay molecules

Signalingmolecule

Activationof cellularresponse

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Signal Transduction

Cell phone rings You listen to your friend

You drive somewhere

Response variable

Sending the Signal

Reception – receptors for hydrophilic molecules

Signal called a ligand

Reception – receptors for hydrophobic molecules

Transduction – relay the signal

• Phosphorylation: adding a phosphate group

• Used to activate proteins already in the cell

Signaling molecule

ReceptorActivated relaymolecule

Inactiveprotein kinase

1 Activeproteinkinase

1

Inactiveprotein kinase

2

ATPADP Active

proteinkinase

2

P

PPP

Inactiveprotein kinase

3

ATPADP Active

proteinkinase

3

P

PPP

i

ATPADP P

ActiveproteinPP

P i

Inactiveprotein

Cellularresponse

Phosphorylation cascadei

• hydrophilic signals

Receptor alerts molecules inside the cell = phosphorylation

Transduction – relay the signal

First messenger

G proteinAdenylylcyclase

GTP

ATPcAMP

Secondmessenger

Proteinkinase A

G protein-coupledreceptor

Cellular responses

Transduction – relay the signal

• Or use second messengers

= small molecules inside cell

• examples: cAMP, ATP, Ca++

Interdigital tissue

1 mm

Response – cell does something

protein (active)Inhibits activity

Mitochondrion

Receptorfor death-signalingmolecule

Inactive proteins

(a) No death signal

Response – ex. No death signal, cell lives

(b) Death signal

Death-signalingmolecule

(inactive)Cellformsblebs

Active Active

Activationcascade

Otherproteases

Nucleases

Response – ex. Death signal, cell undergoes apoptosis

Growth factor

Receptor

Phosphorylationcascade

Reception

Transduction

Activetranscriptionfactor

ResponseP

Inactivetranscriptionfactor

CYTOPLASM

DNA

NUCLEUS mRNA

Gene

Signal transduction = reception, transduction, response

Lecture 4 Summary

1. Cell Signaling Overview (Ch. 9)- Reception- Transduction- Response

2. Sending the signal (Ch. 9)- Contact, paracrine, endocrine, synaptic- Hydrophilic vs. hydrophobic ligands

3. Signal Reception (Ch. 9)

4. Transduction (Ch. 9)- Phosphorylation/dephosphorylation- Cascades/amplification- Second messengers

5. Cellular Response (Ch. 9)

Exam I Review

Actually write down info – I may collect some of this….

For each of the following images, discuss with your partner briefly and agree what the image is showing.

THEN, each person write their own question about this topic – avoid simple questions such as “what is this image” in favor of concepts about the image.

THEN, exchange questions with your neighbor and solve/answer.

Discuss your answers and grade each other.

I may call on specific teams to provide examples of their questions (remember, if I like them, they may appear on the test!)

Photosynthesis:(Endergonic)

Activeproteinkinase

1

Inactiveprotein kinase

2ATP

ADP

Activeproteinkinase

2

P

P

PP

i

1 2 3