Cell-Cell Interactions

Chapter 7

Receptor Proteins

•Cell Surface Receptors – fits specific signal molecule.

–Binding changes shape = response in cell.

Receptor Proteins

Cell Signaling

•Mechanisms of communication:

–Direct Contact

–Paracrine Signaling

–Endocrine Signaling

–Synaptic Signaling

•Autocrine Signaling - bind to specific receptors on own plasma membrane.

Cell Signaling

Intercellular Receptors

•Gene Regulators

–regulate transcription.

•binding site for DNA.

–signal molecule binds receptor, inhibitor released, DNA binding site exposed.

»specific nucleotide sequence = activates specific gene.

Cell Surface Receptors

•Cell Surface Receptors convert extracellular signal to intracellular signal.

–Chemically Gated Ion Channels

•opens when signal binds to it.

–Enzymic Receptors

•signal activates enzyme

Cell Surface Receptors

–G-Protein-Linked Receptors

•GTP binding system.

•Initiate signal in cytoplasm.

Cell Surface Receptors

Initiating the Intracellular Signal

•Many receptors carry signal’s message into the target cell using intracellular mediators.

–cAMP - Used by all animal cells.

–Calcium (Ca++) - Widely used (muscular contraction)

Amplifying the Intracellular Signal

•Most signaling molecules exist in such low concentrations that diffusion across cytoplasm would take great deal of time without amplifying the signal.

–Chain of protein messengers amplify the signal.

Expression of Cell Identity

•During development, each animal cell type acquires a unique set of cell surface molecules.

–Glycolipids

•Blood type

–MHC Proteins

• (Major Histocompatibility Complex)

•Cause immune response in transplants

Intercellular Adhesion

•Cell clusters long-lasting connections with each other (cell junctions).

–connections determine tissue properties

Tight Junctions

•Tight junctions connect plasma membranes of adjacent cells in a sheet.

–Prevent small molecules from leaking between cells and through the sheet.

Anchoring Junctions

•Anchoring junctions mechanically attach cytoskeleton of one cell to cytoskeleton of other cells, or to the extracellular matrix.

Communicating Junctions

•Communication junctions pass chemical signals directly from one cell to adjacent cells.

–Establish direct physical connections.