1. Cell Communication
Keri Muma
Bio 6

2. Types of Cellular Communication
Direct contact between cells
Gap junctions – cells are connected by tunnels formed by connexons
Allows ions and small water soluble chemicals to pass between cells
Cardiac and smooth muscle

3. Types of Cellular Communication
Direct contact between cells
Cell to cell recognition – interaction of cell-surface molecules
Immune cells – recognize self vs. non-self

4. Types of Cell Communication
Through extracellular chemical messengers
Cells release ligands that bind to receptors on target cells to initiate a desired cellular response

5. Types of Cell Communication
Local Regulators
Paracrine – through diffusion, ligands affect cells in the local vicinity
Autocrine – chemicals act on the cell that produced it
Examples: histamine, cytokines, prostaglandins

6. Local Regulators Neurotransmitters – secreted by neurons
Diffuse across the synaptic cleft and target the adjacent cell (neuron, gland, muscle)
Short-lived

7. Types of Cellular Communication
Long-range (distant) regulators
Hormones – secreted into the blood by endocrine glands to travel to distant target cells
Neurohormones – neurons secretes hormones into the blood

8. Cellular Effects of Chemical Signals
Example of various effects chemical signals may have on the target cell
Activate or inhibit enzymes
Direct protein synthesis through activation of transcription factors
Stimulate cell division
Alter membrane permeability – membrane potential or opening/closing of ion channels

9. How do hormones work?
Hormones are chemical substances that travel through the blood to a target cell
Target cells must have specific receptors to which the hormone binds
These receptors may be intracellular or located on the plasma membrane
They trigger a change in cellular activity

10. Types of Hormones Amines – amino acid derivatives Peptides – proteins
Catecholamines (NE and E), T3, T4, serotonin, melatonin
Peptides – proteins
Vasopressin, insulin
Steroids – cholesterol based
Cortisol, aldosterone, estrogen, testosterone
Eicosanoids –derived from arachidonic acid
Prostaglandins, leukotrienes

11. Transport of Hormones
Hydrophilic (water-soluble) hormones – transported dissolved in the plasma
Peptide and catecholamines
Lipophilic (lipid-soluble) hormones – circulate bound to plasma proteins such as albumin
Steroids and thyroid hormones

12. Mechanism of Signaling Molecules
Lipid soluble hormones
Move through the plasma membrane and bind to an intracellular receptor in the nucleus
Binding of the HRC to the DNA triggers transcription of a specific gene and the synthesis of a protein that initiates a cellular response

13. Mechanisms of Signaling Molecules
Water soluble hormones- utilize a membrane bound receptor
Binding of hormone causes a conformational change in the receptor
Two affects of ligands binding to membrane bound receptors:
1.Triggers the opening or closing of ion channels

14. Mechanisms of Signaling MoleculesOR
2.Transfers the signal to a secondary messenger within the cell which triggers a cascade of biochemical events

15. Types of Receptors

16. Signal Transduction

17. Secondary Messenger Pathways
G-protein linked receptor – spans the membrane and is associated with a G protein on the cytoplasmic side
Ligand binds to the receptor
Receptor then activates a G protein
G proteins are considered relay proteins that cycle between an inactive and active form

18. Cyclic AMP Secondary Messenger Pathway
G protein activates the enzyme adenylate cyclase (the effector)
Converts ATP to cyclic AMP
Activates protein kinase A which phosphorylates other proteins
Trigger cellular responses

19. Cyclic AMP Secondary Messenger Pathway

20. Signaling Pathways Amplify the Cells Response to Signals
Molecules in second
messenger system
Total number
of molecules
Extracellular
chemical messenger
bound to membrane
receptor 1
Amplification
Activated
adenylyl cyclase
(10) 10
Amplification
Cyclic AMP
(100)
1,000
Activated
protein kinase
1,000
Phosphorylated
(activated) protein
(e.g., an enzyme)
Amplification
(100)
100,000
Amplification
Products of
activated enzyme
(100)
10,000,000

21. Calcium Secondary Messenger Pathway
1. Binding of extracellular messenger to a G protein linked receptor or a tyrosine kinase receptor
2. Activates phospholipase C which converts PIP2 to DAG and IP3

22. Calcium Secondary Messenger Pathway
3. DAG will activate protein kinase C in another signaling pathway
4. IP3 binds to calcium channels triggering the release of calcium from the ER into the cytoplasm

23. Calcium Secondary Messenger Pathway
5. Calcium binds to and activates calmodulin which can alter other proteins to bring about a cellular response

24. Calcium Secondary Messenger Pathway

25. Calcium Secondary Messenger Pathway

26. Summary of Signaling Pathways