Cellular Odd and Ends

1. Cellular Odd and Ends BIO 201 Kelly Trainor, PhD

2. Membrane Junctions • Three types: • Tight junction • Desmosome • Gap junction

3. Membrane Junctions: Tight Junctions • Impermeable junctions prevent molecules from passing through the intercellular space • Found in epidermal and endodermal tissues and linings

4. 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

5. 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

6. 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

7. 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

8. G-Protein Secondary Messengers

9. 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