Cell communication Premedical biology

The plasma membrane fluid mosaics of lipids and proteins - consists a double layer of phospholipids and other lipids, proteins controls traffic into and out of the cell it surrounds selective permeability - allows sufficient passage of oxygen a nutrients, elimination of wastes

phospholipids are amphipatic molecule membrane proteins are embeded or attached to surface

The fluidity - drift in the plane of the membrane - switch from one phospholipid layer to the other - protein move slowly - unsaturated hydrocarbons – remain fluid - cholesterol (animal cells) reduces membrane fluidity; helps stabilize the membrane

Proteins determine most of the membrane‘s specific functions Integral proteins – transmembrane proteins Peripheral proteins – are not embeded in the lipid bilayer

Intracellular junctions Cell walls perforated with channels called plasmodesma In animals are intracellular junctions. Tight junction Desmosomes Gap junctions Adhere, interact and communicate

Carbohydrates Cell-cell recognition – sorting cell into tissues and organs in embryo - rejection of foreign cells by the immune system - usually short branched oligosaccharides - covalently bonded to proteins

Cell surfaces Plant cells (some protist, prokaryotes, fungi) encased by cell walls the extracellular matrix - ECM Glycoproteins : Colagen fibers embedded in network of proteoglycans fibronectins bind to receptor protein called integrins are built into plasma membrane and bind to microflaments on cytoplasmatic side

Cell communication Cell respond to external signals A signaling molecule binds to a receptor protein, causing to change shape transduction: cascades of molecular interactions Response: signaling lleads to regulation of transcription or cytoplasmatic activities signal transduction pathways

Signal transduction pathways

Cell communication Direct contact between membrane-bound cell-surface molecules – cell junctions - cell-cell recognition Embryo development, immune response Local regulators - paracrine signaling Synaptic signaling - animal nervous system Long distance signaling – chemicals called hormones

Local and long-distance signaling

Cell signaling 1.Reception: target cell’s detection of a signaling molecule coming from outside 2.Transduction: change of the receptor protein initiating process of cellular response 3.Response: cellular activity: catalysis, rearrangement of the cytoskeleton, activation of genes

Reception Signaling molecule - ligand Change of shape – activation and ability to transfer of signal G protein coupled receptors / inhibitory or activity Receptor tyrosine kinases enzymatic activity, catalyse transfer of phosphate groups Ion channel receptors gate open or close

Intracellular receptors for steroid and thyroid hormones, nitric oxide

Transduction Multistep pathway of activation of proteins by addition or removal of phosphate groups or other small molecules or ions that act as messegers – greatly amplifying a signal Phosphorylation and dephosphorylation of proteins system acts as a molecular switch Protein kinase / transfer phosphate groups from ATP to protein

A phosphorylation cascade

Small moleculer and ions as second messengers Nonprotein molecule, can readily spread by diffusion – cAMP and calcium ions Protein are sensitive to the cytosolic concentration of one or other

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

Response Regulation of transcrption or cytoplasmic activities The end of pathway may occur in the nucleus or in the cytoplasm Regulation of synthesis / a transcription factors Regulate the activity or synthesis

Nuclear response to a signal

Cytoplasmic response to a signal

Multiple steps of signal transduction amplify the signal, in each step the number of activated products is much greater provide different points at which response can be regulated Specifity of cell signaling and coordination

Active transport is the pumping of solutes against gradients „uphill“ Major mechanism of ability of cell to maintain internal concentration of small molecules that differ from concentrations in enviroment

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