1. Cell to Cell Communication

2. Why do cells need to communicate?
Cells must communicate to coordinate their activities!! (unicellular AND multicellular)
Cells respond to internal signals (chemical molecules/hormones) AND external signals (detection of light or temperature changes)

3. Unicellular Organism Communication
Signals are typically changes in the environment
Responses are typically changes in gene expression
Ex: Quorum Sensing, Inducible operons, Repressible Operons

4. Quorum Sensing
Ex: Results in Production of Toxins

5. Lac Operon
Responding to changes in the environment

6. Multicellular Signaling Pathways
Allow receiving of information, coordination of ALL of the cells of the organisms in responding to that information
Ex: Fight or Flight Response (Epinephrine)

7. Signal Transduction is UNIVERSAL
All organisms have signal transduction pathways
MAJOR area of evolution!
Heavily adapted by natural selection

8. What are the various ways that cells can communicate?

9. Cell-Cell Contact (Juxtacrine)
Plasmodesmata: Channels in the cell walls of plant-like cells which allow for direct passage of materials and signaling molecules

10. Immune System Cells
Communication between lymphocytes (white blood cells)

11. Paracrine Signaling
Neurotransmitters

12. Interferons in Immune System

13. Endocrine Signaling – Long-Distance
Hormones
Insulin/Glucagon

14. Human Growth Hormone

15. Sex Hormones –Menstrual Cycle
How does birth control work?

16. Sex Hormones - Testosterone

17. What are the three phases of signal transduction?
The process must involve three stages.
Reception, detection of signal
Transduction, transmission of signal
Response, cellular response to the signal

18. What is a ligand?

19. What is a ligand?
A ligand is a signaling molecule involved in the reception stage
Two major classes of ligands: polar (protein based, charged, peptide) and nonpolar (lipid based, steroid)
The chemistry of the ligand determines if it will be received by a receptor on the cell membrane or intracellularly

20. Receptor Proteins
Proteins with a diversity of structures, BUT there are general features:
Area to interact with ligand (MATCHING SHAPE!)
Area that transmits the signal to another protein
Conformational change in shape following ligand interaction

21. Ex: G-Protein-Linked Receptor
A ligand binds to G-protein linked receptor
Conformational change in receptor causes phosphorylation of a G-protein (activation)
Activated G-protein phosphorylates the next protein in the pathway

22. Ex: Ligand-gated Ion Channels
Ligand binds to the channel protein (receptor)
Conformational Change causes the channel to open
Ions move freely into the cell
Change in Ion concentration triggers intracellular responses by changing shapes of various proteins
Very important in NERVOUS SYSTEM

23. Ex: Intracellular Receptors
Can be found in the cytoplasm or the nucleus

24. How do chemical messengers reach these receptors?
Ligand must pass through the cell membrane (nonpolar, lipid based, steroid hormone ligands)

25. Is this a protein or steroid ligand?

26. Is this a protein or steroid ligand?

27. Is this a protein or steroid ligand?

28. STAGE 2: TRANSDUCTION
Transduction converts signal reception into a cellular response
Accomplished by activation of proteins through phosphorylation (kinase enzymes), or a change in intracellular conditions

30. Second Messengers
Internal signaling molecules, often activated by multiple external signals
Aid in amplification of signal
Ex: cyclic AMP (cAMP) and Ca2+.

31. Pathway involving cAMP as a secondary messenger.
Pathway using Ca2+ as a secondary messenger.

32. The Response
Cell responses involve changes in gene expression, and the activation of already synthesized, inactive proteins

33. Ex: Epinephrine

35. Ex: Testosterone: A steroid Hormone
Steroid Hormones (nonpolar ligands) bind to intracellular receptors
These activated proteins act as transcription factors and activate gene expression of male specific genes

36. Benefits of Multiple Steps
They amplify the response to a signal.
They contribute to the specificity of the response.
Allow for multiple points of regulation

37. Do all cells have the same responses to the same signals?
NO!
Different cells have different collections of proteins present and therefore cannot always have the same response

38. Alterations in Signal Transduction Pathways disrupt homeostasis
Diabetes – Type I and Type II
Parkinston’s Syndrome
Cancer
Cholera

43. Short Answer Question
The figure above represents a generalized hormone- signaling pathway. Briefly explain the role of each numbered step in regulating target gene expression.

44. (3 points maximum)
• Step 1 = hormone/ligand binding to receptor to initiate/trigger/induce signaling OR signal reception
• Step 2 = an intracellular cascade that transduces/amplifies/transfers the signal from plasma membrane to nucleus (or other cellular effectors)
• Step 3 = transcription/expression of target genes is stimulated/repressed

45. Many drugs work by altering signal transduction pathways
Antihistamines
Birth Control