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Warm-Up

Warm-Up. Why do you communicate? How do you communicate? How do you think cells communicate? Do you think bacteria can communicate? Explain. Warm-Up. Compare the structure & function of these receptor proteins: GPCR, tyrosine kinase and ligand-gated ion channels.

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Warm-Up

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  1. Warm-Up • Why do you communicate? • How do you communicate? • How do you think cells communicate? • Do you think bacteria can communicate? Explain.

  2. Warm-Up • Compare the structure & function of these receptor proteins: GPCR, tyrosine kinase and ligand-gated ion channels. • What is a second messenger? What are some examples of these molecules? • What are the possible responses to signal transduction in a cell?

  3. Cell Communication CHAPTER 11

  4. Do bacteria communicate? Bonnie Bassler on How Bacteria “Talk”

  5. Video Questions: • Why are scientists studying how bacteria (and not just human cells) communicate? • What is quorum sensing? • Describe how Vibrio fischeri use quorum sensing in squid. • According to Bonnie Bassler (Princeton University), what are scientists hoping to use as the next class of antibiotics?

  6. Cell Signaling Animal cells communicate by: • Direct contact (gap junctions)-passing between adjacent cells • Secreting local regulators—interactions between molecules protuding from surfaces. • Long distance (hormones)-Endocrine glands

  7. Paracrine---secreting cells act on a nearby target cell by secreting molecules of regulation (growth factor) • Synaptic—a nerve cell releasing neurotransmitters into a synapse to stimulate a muscle or another nerve cell • Endocrine– specialized endocrine cells secrete hormones into body fluids

  8. 3 Stages of Cell Signaling: • Reception: Detection of a signal molecule (ligand) coming from outside the cell. • Transduction: Convert signal to a form that can bring about a cellular response • Response: Cellular response to the signal molecule

  9. Reception A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell’s surface or (inside the cell).

  10. 1. Reception • Binding between signal molecule (ligand) + receptor is highly specific. • Types of Receptors: • Plasma membrane receptor • water-soluble ligands • Intracellular receptors(cytoplasm, nucleus) • hydrophobic or small ligands • Eg. testosterone or nitric oxide (NO) • Ligand binds to receptor protein  protein changes SHAPE  initiates transduction signal

  11. 3Types of Plasma Membrane Receptors

  12. G-Protein-Coupled Receptor

  13. Receptor Tyrosine Kinase

  14. Ligand-Gated Ion Channel

  15. 2. Transduction • Cascades of molecular interactions relay signals from receptors  target molecules • Protein kinase: enzyme that phosphorylates and activates proteins at next level • Phosphorylation cascade: enhance and amplify signal

  16. Transduction • The signaling molecule changes the receptor protein that will result in a specific cellular response. • Can be a single step or a series of steps called a signal transduction pathway

  17. Response The transduced signal triggers a specific cellular response. Signaling ensure the right cells get the right signal at the right time and in proper coordination with activities of other cells.

  18. Second Messengers • small, nonprotein molecules/ions that can relay signal inside cell • Eg. cyclic AMP (cAMP), calcium ions (Ca2+), inositol triphosphate (IP3)

  19. cAMP • cAMP = cyclic adenosine monophosphate • GPCR  adenylyl cyclase (convert ATP  cAMP)  activate protein kinase A

  20. 3. Response • Regulate protein synthesis by turning on/off genes in nucleus (gene expression) • Regulate activity of proteins in cytoplasm

  21. An Example of Cell Communication http://learn.genetics.utah.edu/content/cells/cellcom/

  22. Signal Transduction Pathway Problems/Defects: Examples: • Diabetes • Cholera • Autoimmune disease • Cancer • Neurotoxins, poisons, pesticides • Drugs (anesthetics, antihistamines, blood pressure meds)

  23. Cholera • Disease acquired by drinking contaminated water (w/human feces) • Bacteria (Vibrio cholerae) colonizes lining of small intestine and produces toxin • Toxin modifies G-protein involved in regulating salt & water secretion • G protein stuck in active form  intestinal cells secrete salts, water • Infected person develops profuse diarrhea and could die from loss of water and salts

  24. Viagra • Used as treatment for erectile dysfunction • Inhibits hydrolysis of cGMP  GMP • Prolongs signal to relax smooth muscle in artery walls; increase blood flow to penis

  25. Viagra inhibits cGMP breakdown

  26. Apoptosis = cell suicide • Cell is dismantled and digested • Triggered by signals that activate cascade of “suicide” proteins (caspase) • Why? • Protect neighboring cells from damage • Animal development & maintenance • May be involved in some diseases (Parkinson’s, Alzheimer’s)

  27. Apoptosis of a human white blood cell Left: Normal WBC Right: WBC undergoing apoptosis – shrinking and forming lobes (“blebs”)

  28. Effect of apoptosis during paw development in the mouse

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