Cell Communication Chapter 11 - Abridged. Slide 2 of 23 Cell-to-Cell Communication Critical for multicellular organisms Trillions of cells must communicate.

Cell Communication

Chapter 11 - Abridged

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Cell-to-Cell Communication

Critical for multicellular organisms Trillions of cells must communicate in order to

coordinate their activities

Recent research indicates: cancer results from corrupted communication

Unimportant for the AP Exam Crucial for understanding the breakthroughs in cancer

and genetics that are occurring almost monthly now

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Recent Nobel Prizes in Medicine

2001 – Hartwell, Hunt, & Nurse – cyclin pathways and cell cycle regulation (yeast)

2002 – Brenner, Sulston, Horvitz – used C. elegans to elucidate the mechanism of apoptosis

2006 – Fire & Mello - used C.elegans to discover the pathway of RNA interference

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Simon Sez…

Signaling is a lot like the game “Simon Says…”

The signal is received: the game players hear: “Simon says take a step forward”

The signal is transduced: players must decide whether to step forward or not

The signal elicits a response: players step forward if the command was preceded by “Simon says”

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3 Stages of Signaling

Thesis: external signals are received & converted to responses within the cell

1. Reception Signaling molecule binds to receptor protein = Shape Change

2. Transduction Cascades of molecular interactions relay signals from

receptor proteins to target molecules in the cell

3. Response Regulation of transcription or cytoplasmic activities

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1st form of signaling

Yeast (fungi) mating

Process:1.Release mating factor2.Receive complementary factor3.????4.Response: grow toward opp. Type5.Nuclei fuse = genetic recombination

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Overview of Cell Signaling

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View Animation

11_06 SignalingOverview_A.swf

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Reception

Reception involves getting the signal to the correct receiver

Only certain cells have the correct receptor = only certain cells can receive the signal

Signaling molecule usually called ligand receptor-ligand binding causes a conformational change

in the receptor molecule (remember induced fit?) Conformational change = Activation of the receptor

molecule

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2 Types of Signal Receptors

1. Plasma Membrane Receptors Hydrophilic or water-soluble ligands or signal molecules G Protein-Coupled Receptors (GPCR) Receptor Tyrosine Kinase (RTK) Ion Channel Receptors

2. Intracellular Receptors

Hydrophobic or Nonpolar ligands

Carry out transduction by themselves

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View Animation

11_13SignalTransduction_A.swf

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G Protein-Coupled Receptor

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Receptor Tyrosine Kinase (RTK)

Amplification

Kinase = enzyme for transfer of phosphate group

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Ligand-Gated Ion Channel

Membrane receptor with a region that acts as a “gate” when the receptor changes shape.

When the signal molecule binds, gate opens or closes

Important in the nervous system

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Intracellular Receptor

Hydrophobic signal molecules

Testosterone

Most intracellular receptor signals do the entire transduction on their own

Testosterone behaving as a transcription factor

-- controls which genes (DNA) are transcribed into mRNA

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Transduction

Multistep Pathway

Transduction = shape change

Signal amplification

Signal Transduction Pathways often involve a phosphorylation cascade

Molecule is phosphorylated = activated Phosphate removed = deactivation

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Protein Kinases (PK) -- enzymes that transfer phosphate groups

Protein Phosphatases (PP) -- enzymes that remove phosphate groups

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Second Messengers

1st messenger = receptor Only GPCR & RTK have 2nd messengers

Other important component of transduction pathways Most components are enzymes or proteins

Small & polar

Calcium Ions & Cyclic AMP

Initiate a phosphorylation cascade

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Response

Response may occur in the cytoplasm or nucleus

2 Types of typical response:1. Enzyme activity is regulated (turned on or off)2. Synthesis of enzymes is regulated (promoted or inhibited)

Transcription Factors – control which genes are transcribed (DNA RNA)

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Transcription Factors

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GF = Growth factor

RTK = Receptor Tyrosine Kinase

Ras = G Protein Associated with tumor growth

Rho = G protein

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RTK = Receptor Tyrosine Kinase

GPCR – G-protein coupled receptor

Apoptosis = Programmed cell death

PDK1 = Protein dehydrogenase kinase

Akt = Protein kinase -- Involved in apoptosis

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Day 1 Complete