Cell communication is vital to unicellular and multicellular organisms

Transcription

1 Cell Communication

2 Cell communication is vital to unicellular and multicellular organisms Bacteria can sense their environment (nutrient availability) and communicate with other bacteria Multicellular organisms communicate with their surroundings And within their bodies To coordinate activities

3 When cell communication goes wrong? LOSING THE SIGNAL Type 1 Diabetes Pancreas insulin producing cells are lost WHEN THE SIGNAL DOESN T REACH ITS TARGET Multiple sclerosis Nerve cells are damage and cant Transmit a signal

4 When cell communication goes wrong? WHEN TARGET CELLS IGNORE SIGNAL Type 2 Diabetes Insulin cells produce insulin but Target cells don t respond to it MULTIPLE BREAKDOWNS Cancerous cells don t respond to many signals or start producing abnormal Signals

5 Types of cell communication Local signaling - gap junctions and plasmodesmata allow molecules to pass between cells - cells can communicate via molecules that protrude from their surfaces immunity and embryo - secreting signals paracrine synaptic Long distance endocrine

6 Overview of the three stages of Cell signaling 1. Reception: Target cells detects the signal, by signal-receptor binding (this receptor molecule can be located on the plasma membrane or inside the cell) 2. Transduction: this binging changes the shape of the receptor protein, starting a signal transduction pathway via relay molecules 3. Response: the transduction pathway finally triggers a specific cellular response (like catalysis by an enzyme, activation of specific genes)

7 Types of reception: intracellular receptors or cell surface receptors Binding between the signal molecule (ligand) and receptor is highly specific Cell surface receptor: receptor protein located on the plasma membrane ligand is a hydrophilic molecule proteins (growth factors) amino acids, peptides (neurotransmitters) Intracellular receptors: receptor protein located in cytoplasm or nucleus ligand is hydrophobic molecules (steroids) or small enough (NO, nitric oxide gas)

8 Example of Intracellular signaling

9 Types of cell surface receptors A) Ligand-gated ion channels: open and close in response to a signal regulating the flow of ions (nerve impulse) B) G protein-coupled receptors (GPCRs): ligand activates receptor which activates a cytoplasmic G protein (protein with a GDP) Widespread in function: embryo development, sensory reception. Bacteria make people ill by producing toxins that interfere with G protein s function 60% of medicines influence G protein related pathways C) Enzyme-linked receptors: receptor has an enzymatic activity Example: Receptor tyrosine kinases (RTK) abnormal functioning of RTK are associated with cancer

10 G protein-coupled receptors

11 Receptor Tyrosine Kinases

12 Tyrosine-kinase receptors and G protein-coupled receptors are involved in the cell cycle How are the two similar? How are they different?

13 Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell In a signal transduction pathway: The message is passed on from one molecule to the next by a change in shape. May involve Phosphorylation cascades: a series of protein kinases (via phosphorylation or dephosphorylation) Second messengers: Small molecules like cyclic AMP Or calcium ions Diffuse readily through cytosol and Broadcast signals quickly

14 Phosphorylation cascades Many pathways involve phosphorylation cascades: Protein kinases add a phosphate group to the next kinase/protein activating it Other enzymes called protein Phosphatase remove phosphate groups The balance of between phosphorylation and dephosphorylation regulates the proteins in the signal transduction pathway

15 Second messengers: relay messages but also amplify the strength of the signal Many G proteins activate Adenylyl cyclase, catalyzing ATP camp - camp activates a protein kinase - Glucagon produced by pancreas increases blood glucose levels In some G protein receptor and receptor tyrosine kinases the signal opens a calcium gated channel - Muscle contraction

16 Can both secondary messengers operate in the same signal transduction pathway? How are they different?

17 Response: cell signaling leads to regulation of transcription or cytoplasmic activities Some pathways lead to a nuclear response: specific genes are turned on or off Via transcription factors In others, the response involves cytoplasmic regulation

18 Response: depends on the signal and the target cell Compare liver cell and heart muscle cell, Are they both in contact with the signals (hormones) that flow in the blood stream? Do both react to all the different signals flowing in the blood stream? Both cells have receptors for the same signal, will they respond equally? Why?

19 Apoptosis: integrates multiple cell signaling pathways Apoptosis is a programmed cell death mechanism characterized by depolymerization of cytoskeleton, cell shrinkage, chromatin condensation, nuclear fragmentation

20 Multiple signaling pathways by Activation of death receptors or Internal proteins Will lead to a caspase cascade activation (caspases are enzymes that breakdown proteins) and eventually cell death. Apoptosis prevents damaged cells from consuming essential nutrients and spreading infection. Application Increases in apoptotic activity are hallmarks of several disease states including AIDS, Parkinsons and alzheimers, Type 1 diabetes Cancer cells can result from Decrease in apoptotic activity

21 Effect of apoptosis during development

22 Yeast used in meisois and cell replication C. elegans used in apoptosis