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

Organelles

cells

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

Cell-membrane

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