Chapter 15 Baboon text Cell Signaling and Communication

15.1 What Are Signals, and How Do Cells Respond to Them?

Cells receive signals from

1. Physical environment

Ex: light, temperature, touch, sound and chemicals

2. Other cells- primarily in the form of chemicals and touch.

15.1 What Are Signals, and How Do Cells Respond to Them?

Autocrine signals affect the cells that made them.

Paracrine signals affect nearby cells.

Hormones travel to distant cells, usually via the circulatory system.

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e.g., Histamine released from damaged cells in inflammation

e.g., Interferon release by viral-infected cells

Receptor proteins have very specific binding sites for chemical signal molecules, or ligands.

Binding the ligand causes receptor protein to change shape.

The binding is reversible.

LIGANDS

LIGANDS• Ligands can bind to

– Cytoplasmic receptor- located in the cytoplasm or nucleus. Ligand must be small and non-polar (lipid soluble)• Cytoplasmic- causes change in protein regulation

– Ex: glycogen breakdown• Nuclear- stimulates or inhibits transcription

– Membrane receptor- located within the membrane. Ligand is large and/or polar (water soluble)• Leads to stimulation or inhibition of transcription;

either stopping, starting, increasing or decreasing production of particular activity

e.g., nitric oxide andsteroid hormone

Intracellular ReceptionExtracellular Reception

Ligands

e.g., insulin and epinephrine

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Three Stages of Signal Transduction

1. Reception of extracellular signal by cell

2. Transduction of signal from outside of cell to inside of cell—often multi-stepped

Note not necessarily transduction of ligand

3. Cellular Response

Response is inititiated and/or occurs entirely within receiving cell

Three Stages of Signal Transduction

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2a. Transduction

2b. Transduction

1. Reception

3. Response

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2b. Transduction

2c. Transduction

2d. Transduction

1. Reception

3. Response

Responses usually involve increasing or decreasing some Protein’s Function

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Note that more than one response can result from the reception of a single ligand

A signal transduction pathway:

A signal transduction pathway:

• The signal causes receptor protein to change conformation.

• Conformation change gives it protein kinase activity.

• Phosphorylation alters function of a responder protein.V

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15.2 How Do Signal Receptors Initiate a Cellular Response?

Types of plasma membrane receptors:

• Ion channels

• Protein kinases (Tyrosine-kinase receptors)

• G protein-linked receptors

15.2 How Do Signal Receptors Initiate a Cellular Response?

Ion channel receptors: channel proteins that allow ions to enter or leave a cell.

Example: acetylcholine binds which allows Na+ into cell. This causes a muscle to contract

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Figure 15.5 A Gated Ion Channel

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15.2 How Do Signal Receptors Initiate a Cellular Response?

G protein-linked receptors: the seven-transmembrane-spanning G protein-linked receptors.

G proteins: mobile membrane proteins with three subunits.

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15.2 How Do Signal Receptors Initiate a Cellular Response?

Signal outside cell activates G protein linked receptor which activates G protein inside cell.

This then activates the protein and it moves through plasma membrane until it encounters an effector protein.

Binding activates the effector which causes a change in cell function (activation/inhibition).

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Figure 15.7 A G Protein-Linked Receptor (Part 1)

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Effector protein can cause amplification

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the more ligand binding, the more K+

in cytoplasm

note how activation is reversible

15.3 How Is a Response to a Signal Transduced through the Cell?

Protein kinase receptors—catalyze the transfer phosphate from ATP to a target protein causing conformation and activity.

Ex: Insulin (ligand) binds to receptor which phosphorylates and activates glucose transporters.

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Figure 15.10 A Protein Kinase Cascade•

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15.3 How Is a Response to a Signal Transduced through the Cell?

Direct transduction- the receptor causes the change and occurs at membrane.

Signal Amplification (Indirect Cascade)

15.3 How Is a Response to a Signal Transduced through the Cell?

Indirect transduction- involves a second messenger.

15.3 How Is a Response to a Signal Transduced through the Cell?

Second messengers were discovered in research on the liver enzyme glycogen phosphorylase, and how it is activated by epinephrine. (Read up on Sutherland’s investigations with epinephrine p. 340-41)

Binding of the hormone to the membrane receptor caused production of a small molecule (cyclic AMP, or cAMP) that diffused into the cytoplasm to activate the enzyme.

15.3 How Is a Response to a Signal Transduced through the Cell?

The signal is the first messenger.The second messenger is released into the

cytoplasm after signal binds to receptor.Second messengers affect many processes in

the cell.Also amplify the signal—one epinephrine

molecule leads to production of many cAMP.

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1. Note how same ligand gives rise to different responses

2. Cells differ in terms of their proteins3. Different proteins respond differently to the same

environmental signals4. (note, though, same receptors, different relay)5. Different cells behave differently because some,

but not all proteins can differ between cell types

Chemical Signaling Between Cells

15.4 How Do Cells Change in Response to Signals?

• In your trifold book add the following information:

• Include details on the front and examples for each on the back.

Reception Transduction Response

Ion channels

G-Protein Linked

Protein Kinase

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biology.ucf.edu/courses/bsc2010/08-2010C-02.PPTwww.aw.com/bc/ppt/marieb_ap/chap03c.ppthttp://zeus.uwindsor.ca/courses/biology/zielinski/204/comm1.ppthttp://vaccine.chonbuk.ac.kr/images/cell/Chapter%2015%20Cell.ppthttp://faculty.uca.edu/~jmurray/BIOL1440/lec/lec15.ppt\http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/7-signal.ppthttp://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/9-glycogen.ppthttp://homepage.smc.edu/chen_thomas/Bio21/Chpt%2011%20Cell%20Comm.ppt

Putting the information to work

Cell Cycle Control System

• How is the cell cycle controlled• Restriction Checkpoints- sites where cell division

are either prevented or stopped• Locations

– G1- commits the cell to division– G2– M– Ex: At the G1 checkpoint, if the cycle is stopped, cell

will enter G0

• Checkpoints are controlled by protein activity– 2 main proteins

• Cyclins- proteins continually produced in cells

• Kinase-proteins that activate or inactivate target proteins by phosphorylating them

– Phosphorylation: breaking down ATP and adding a phosphate group

» This changes the shape of the target protein

Target proteins –directly regulate the cell cycle

Cell Cycle Control System

• Ex: G1 checkpoint• Proteins involved

– Cyclin– Cyclin dependent kinase (Cdk)– Rb (target protein) normally inhibits the cell cycle at G1 checkpoint

How it worksWhen Cdk binds with a cyclin, it becomes activatedCdk/cyclin complex phosphorylates RBRb becomes inactive and can no longer inhibit the cell cycleCell proceeds to stage SynthesisNOTE: RB and other target proteins in the cell cycle control system act as

tumor suppressors by stopping uncontrolled cell division.LOOK AT FIGURE 9.6 IN YOUR BABOON TEXT

Cell Cycle Control System

• LOOK AT FIGURE 9.6 IN YOUR BABOON TEXT