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.