Membrane surrounding the cell
Everything that’s inside the cell
Fluid inside the cell.
Solid structures in the cell
Contains DNA instructions for the cell
Characteristics of plasma membrane
- Composed of phospholipid bilayer.
- *Selectively permeable allowing transfer of substances
Functions of plasma membrane:
- *Barrier between internal and external environment of the cell.
- *Movement of substance in and out of a cell
- *Cellular communication
Arrangement of membrane proteins:
- *Integral proteins- embedded. This includes the trans membrane protein.
- *Peripheral proteins- located on the outside surface
Membrane proteins serve many functions:
- *Ion channels
- Cell identity markers.
- *MHC proteins.
- *Phospholipids are in constant motion.
- *Plasma membrane and its components can move.
- *Allows for movement of membrane during growth, maintenance, and repair
- Some molecules can cross plasma membrane and others can’t.
- *But Ion channels and transporters alter permeability.
- *Permeable to small, uncharged nonpolar molecules. Examples are oxygen and carbon dioxide.
- *Weakly permeable to small, uncharged polar molecules. Example is water.
- Impermeable to ions and large molecules.
Gradients across the membrane
*Dependent on selective permeability.
- *Concentration gradient
- *Electrical gradients (membrane potential).
- *Mostly positive (+) outside and negative (-) inside a resting membrane potential.
- Requires energy input from the cell
- *A substance is driven against its concentration or electrical gradient.
- *ECF has less solutes than ICF.
- *H2O enters cell faster than it leaves
- *Cell swells and may burst (lyse).
- ECF has more solutes than ICF.
- *Water leaves faster than it enters
- *Cell shrinks (crenation).
Mechanism of passive transport (no energy
- Simple diffusion
- *Facilitated diffusion