General Biology/Cells/Cell-Cell Interactions

Cell-cell interactions Cells interact with the environment and with each other. Cell signaling Signaling requires Signal Cell receptor (usually on the surface of a membrane) Signaling is important in: Response to environmental stimuli Sex Development Major area of research in biology today Types of signaling Direct contact (e.g., gap junctions between cells) Paracrine: Diffusion of signal molecules in extracellular fluid; highly local Endocrine: Signal (hormone) molecule travels through circulatory system Synaptic: neurotransmitters Types of signal molecules Hormones: chemically diverse Steroid Polypeptide Vitamin/amino acid derived Cell surface proteins/glycoproteins Ca2+, NO Neurotransmitter Several hundred types Some are also hormones e.g. Estrogen, progesterone Receptor molecules Intracellular Protein that binds signal molecule in cytoplasm Bound receptor may act as: Gene regulator Enzyme Cell surface Gated ion channels (neurotransmitter receptor) Enzymic receptors G protein-linked receptors Cell surface protein Tissue identity glycolipids MHC proteins Immune systems distinguish self from not-self Intercellular adhesion permanent contact help form sheets of cells, tissues may permit signaling Example: G proteins Transmembrane surface receptor binds signal molecule Conformational change allows binding of G protein on cytoplasmic side G protein binds GTP, becomes activated G protein activates intracellular signal cascade Change in gene expression Secrection Many other possible consequences Communicating junctions Gap junctions animals small molecules and ions may pass Plasmodesmata plants lined with plasma membrane permit passage of water, sugars, etc. Gap junctions This text is based on notes very generously donated by Dr. Paul Doerder, Ph.D., of the Cleveland State University.