Cellular Odd and Ends

BIO 201Kelly Trainor, PhD

Membrane Junctions Three types:

Tight junction Desmosome Gap junction

Membrane Junctions: Tight Junctions Impermeable junctions prevent molecules from passing through the

intercellular space Found in epidermal and endodermal tissues and linings

Membrane Junctions: Desmosomes Anchoring junctions bind adjacent cells together and help form an

internal tension-reducing network of fibers “Rivets” or “spot-welds” that anchor cells together

Found in tissues that move and expand such as the bladder

Membrane Junctions: Gap Junctions Transmembrane proteins form pores that allow ions and small

molecules to pass from one cell to the next for intercellular communication Found in cardiac or smooth muscle cells

Roles of Cell Adhesion Molecules Anchor cells to extracellular matrix or to each other Assist in movement of cells past one another CAMs of blood vessel lining attract white blood cells to injured or

infected areas Stimulate synthesis or degradation of adhesive membrane junctions Transmit intracellular signals to direct cell migration, proliferation,

and specialization

Roles of Membrane Receptors Contact signaling—touching and recognition of cells; e.g., in normal

development and immunity Chemical signaling—interaction between receptors and ligands

(neurotransmitters, hormones and paracrines) to alter activity of cell proteins (e.g., enzymes or chemically gated ion channels)

G protein–linked receptors—ligand binding activates a G protein, affecting an ion channel or enzyme or causing the release of an internal second messenger, such as cyclic AMP

Motor Molecules Protein complexes that function

in movement of organelles and contraction

Powered by ATP Examples include:

Myosin - responsible for muscle contraction

Kinesin - moves cargo inside cells away from the nucleus along microtubules

Dynein - produces the beating of cilia and flagella and also transports cargo along microtubules towards the cell nucleus