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Cell Communication Chapter 11 - Abridged.

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1 Cell Communication Chapter 11 - Abridged

2 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

3 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

4 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”

5 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

6 1st form of signaling  Yeast (fungi) mating Process: Release mating factor Receive complementary factor ???? Response: grow toward opp. Type Nuclei fuse = genetic recombination

7 Overview of Cell Signaling

8 View Animation 11_06 SignalingOverview_A.swf

9 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

10 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

11 View Animation 11_13SignalTransduction_A.swf

12 G Protein-Coupled Receptor

13 Receptor Tyrosine Kinase (RTK)
Amplification Kinase = enzyme for transfer of phosphate group

14 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

15 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

16 Transduction Multistep Pathway Transduction = shape change
Signal amplification Signal Transduction Pathways often involve a phosphorylation cascade Molecule is phosphorylated = activated Phosphate removed = deactivation

17 Protein Kinases (PK) -- enzymes that transfer phosphate groups Protein Phosphatases (PP) -- enzymes that remove phosphate groups

18 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

19 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)

20 Transcription Factors

21 GF = Growth factor RTK = Receptor Tyrosine Kinase Ras = G Protein Associated with tumor growth Rho = G protein

22 RTK = Receptor Tyrosine Kinase
GPCR – G-protein coupled receptor PDK1 = Protein dehydrogenase kinase Akt = Protein kinase -- Involved in apoptosis Apoptosis = Programmed cell death

23 Day 1 Complete


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