The Cell
Cell Tour
Membrane Structure & Function
Microscopy
Light Microscopy
Electron Microscope: focuses a beam of electrons through the specimen or onto its surface
Scanning Electron Microscopy: useful for detailed study of topography; scans the surface that is usually covered with thin film of gold
Transmission Electron Microscopy: used to study the internal structure of cells; specimen has been stained with atoms of heavy metal
Fluorescence: locations of specific molecules in cell can be revealed by labeling the molecules with fluorescent dyes or antibodies
Differential interference contrast: used to exaggerate differences in density
Phase-contrast: variations in density within the specimen are amplified to enhance contrast in unstained cells
Brightfield (stained specimen): staining with various dyes enhances contrast
Brightfield (unstained specimen): light passes directly through the specimen
Cell Fractionation: used for studying the cell being able to separate cell components based on size and density
Surface area vs. Volume ratio
-gets smaller as the cell gets larger
-if cells grows to certain limit then materials would not be able to travel across the surface
Organelles
Prokaryotic vs. Eukaryotic
Membrane Proteins
Integral proteins: penetrate the hydrophobic interior of the lipid bilayer
Peripheral proteins: not embedded in bilayer; are loosely bound to the surface of membrane
Membrane Functions
Enzymatic: protein built into membrane may be an enzyme with its active site exposed to substances in adjacent solutions
Signal: membrane protein receptor may have a binding site with specific shape that fits the shape of a chemical messenger
Transport: may provide a hydrophilic channel across the membrane that is slective
Cell-cell Recognition: glyco-proteins serve as identification tags that are specifically recognized by membrane proteins of other cells
Intercellular Joining: proteins of adjacent cells may hook together in various kinds of junctions
Attachment to Cytoskeleton: microfilaments or other elements of the cytoskeleton may noncovalently bound to membrane proteins; helpms maintain cell shape
Membrane Structure
Diffusion Relationships: Osmosis and tonicity are larger water molecules that move across the membrane by simple diffusion
Active Transport: the pumping of solute across a membrane against its gradient which requires work; the cell must expand energy
Types of Active Transport
Exocytosis
Endocytosis
Sodium-potassium pump