Cell communication

1. Cell communication Premedical Biology

2. The plasma membrane • is fluid mosaics of lipids and proteins, it consists of double layer of phospholipids and other lipids with attached proteins. • controls traffic into and out of the cell it surrounds • is selectively permeable, it allows sufficient passage of oxygen a nutrients and elimination of wastes

3. Lipids and proteins Phospholipids are amphipatic molecules Proteins are embeded or attached to surface.

5. Is due to the presence of unsaturated hydrocarbons, which increase fluidity and cholesterol (animal cells), which reduces fluidity; helps stabilize the membrane The fluidity

6. Proteinsin membrane determine many of the membrane‘s specific functions Integral proteins – transmembrane proteins Peripheral proteins – are not embeded in the lipid bilayer

7. Transport

8. Active transport is the pumping of solutes against concentration gradients „uphill“ It is the major mechanism of ability of cell to maintain internal concentrations of small molecules that differ from concentrations in environment.

9. Cell communication – function of proteins Direct contact between membranes by cell-surface molecules = cell junctions = intracellular joining = cell-cell recognition (glycolipids and glycoproteins)

10. Intracellular junctions(joining) Cell walls of plant cells perforated with channels called plasmodesma. In animals are intracellular junctions. Tight junction Desmosomes Gap junctions Adhere, interact and communicate

11. Cell-cell recognition is done also by carbohydrates(linked to proteins and lipids), which helps to sort cell into tissues and organs in embryo and helps to recognize and reject the foreign cells in the immune system Carbohydrates are usually short branched oligosaccharides.

12. Attachment with ECM Plant cells (some Protists, prokaryotes, fungi) encased by cell walls Animal extracellular matrix – ECM with glycoproteins : Collagen fibers are embedded in network of proteoglycans. Fibronectins bind to receptor protein called integrins in plasma membrane. Integrins bind to microfilaments (cytoskeletal pr.) on cytoplasmatic side.

13. Signal transduction pathways

14. Cell communication: Local and long-distance signaling

15. Cell communication and signal transduction function of protein Cell responds to external signals. A signaling molecule (ligand/first messenger) binds to a receptor protein in membrane and causes a change of his shape (enzyme). On internal side is the signal transformed in the cascade of molecular interactions with origin of second messengers. In nucleus signal leads to regulation of transcription or other cytoplasmatic activities.

16. Cell signaling • Reception: target cell detects a signaling molecule coming from outside • Transduction: change of the receptor protein initiating process of cellular response (enzymatic) • Response: cellular activity: catalysis, rearrangement of the cytoskeleton, activation of genes

18. Reception Signaling molecule + Receptor Receptor or protein associated with get activated and it is able to transfer the signal inside the cell. G protein coupled receptors / inhibitory or activity Receptor tyrosine kinases have enzymatic activity and catalyze transfer of phosphate groups Ion channel receptors withgate open or close

19. Intracellular receptors for steroid and thyroid hormones, nitric oxide

20. Transduction Multistep pathway (cascade) of activation of proteins by addition or removal of phosphate groups or it starts by the origin of small molecules or ions that act as seconder messengers. Phosphorylation and dephosphorylation of proteins acts as a molecular switch. Protein kinases transfer phosphate groups from ATP to protein.

21. A phosphorylation cascade

22. Multiple steps of signal transduction greatlyamplify the signal. In each step the number of activated products is much greater than one step before. Multiple steps also provide different points, at which the response can be regulated and also provide a specifity of cell signaling and coordination.

23. Small molecules and ions as second messengers Nonprotein molecule, which can be spreaded by diffusion – cAMP and calcium ions Protein are sensitive to the cytosolic concentration of one or other.

24. Second messengers: calcium ions and Inositol Triphosphate Neurotransmitters, growth factors, hormones induce cell’s responses via signal transduction pathways that increase the concentration of calcium ions. Responses: muscle contraction, secretion of substances, cell division Second messengers: inositol triphosphate and diacylglycerol

25. Responses: The end of pathway may occur in the nucleus or in the cytoplasm = the change of transcription or cytoplasmic activities. Response in nucleus is the regulation the activity and synthesis - transcription factors

26. Nuclear response to a signal

27. Cytoplasmic response to the signal

28. Thank you for your attention Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson, Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings Publishing Company, 1996 –2010.