C. Organelles
➢ Each organelle has its own special task
➢ Plasma Membrane
- Outer envelope
- Complex
- Phospholipid bilayer
- Encloses vacuole
- Regulates movement in/out of cell
- Flexible due to weak bonds holding it together
■ Higher fluidity when more phospholipids have double bonds (causing a bend in the tail) since the molecules aren’t as packed
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- Semipermeable
■ Only small hydrophobic molecules can pass through unaided
■ Anything large/hydrophilic must pass through active/passive transport
■ Water can’t move through easily due to its polarity - Fluid-mosaic model
■ Peripheral proteins are loosely associated with the lipid bilayer
● Located on inner/outer surface of membrane
■ Integral proteins are firmly bound into the plasma membrane
● Amphipathic to allow anchoring
● Some extend all the way through the membrane
■ Membrane peppered with different proteins/carb chains - Adhesion proteins
■ membrane proteins form junctions between adjacent cells - Receptor proteins
■ Serve as docking sites for arrivals at the cell
■ Ex. hormones - Transport proteins
■ Form pumps that use ATP to actively transport solutes across the membrane
■ Hydrophilic channel that certain molecules/ions can use as a tunnel
■ Specific for substance it moves - Carrier Proteins
■ Bind to molecules and change shape to shuttle them across the membrane
○ Channel proteins
■ Selectively allow the passage of ions/molecules
○ Cell surface marker
■ Exposed on cellular surface
■ Play a role in cell recognition/adhesion
■ Ex. glycoproteins - Carbohydrate side chains
■ Attached to surface of some proteins
■ Found only on outer surface - Cholesterol
■ Maintain fluidity (see pg. 11)
■ Unsaturated fats also lend membrane fluidity by increasing space between phospholipids due to bend
- Semipermeable
