1.5 - Plasma Membrane

Phospholipid Bi-layer

Two-layered arrangement of phosphate and lipid molecules that form a cell membrane, the hydrophobic lipid ends facing inward and the hydrophilic phosphate ends facing outward.

Also contain proteins and cholesterol throughout the structure.

Fluid Mosaic Model vs Sandwich Model

Fluid Mosaic Model (better) - Shows that the proteins are embedded within the phospholipid bilayer

Sandwich Model - Shows that the proteins are on top of the bilayers with only the phospholipids inside

How can substances move in and out of a cell?

Osmosis - Passive movement of water through as semipermeable membrane

Diffusion - Passive movement of any substance from an area of high concentration to a low concentration

Facilitated Diffusion - Proteins in the membrane that allow the passage of otherwise restricted molecules

Active Transport (bulk flow) - Using energy (ATP) to 'pump' molecules across the membrane against the concentration gradient

Endocytosis - Cells take in substances from outside of the cell by engulfing them in a vesicle

Exocytosis - Release of molecules from the cell

What are the '-tonic' solutions?

Isotonic - The water and solute concentration are the same outside and inside the cell. Water enters and exits at the same rate

Hypertonic (shrink) - The water concentration is greater inside the cell and the solute concentration is then greater outside the cell. Water flows out of the cell

Hypotonic (explode) - The water concentration is greater outside of the cell; the solute concentration is greater inside the cell. Water flows into the cell

Diffusion

Passive (no energy required)

Moves from a higher concentration to a lower concentration

Facilitated Diffusion

Passive (no energy required)

Moves from high to low concentration via a protein channel

Speeds up diffusion

Moves along concentration gradient

Active Transport

Active (requires energy) (ATP?)

Requires energy that allows for the carrier protein to take in the molecule at one end and expel it through the other (on the opposing side of the cell)

Moves substance against concentration gradient

Endocytosis + Exocytosis

Phagocytosis and Pinocytosis

Phago - Solid material enclosed in vesicle (e.g. apoptotic bodies)

Pino - Liquid droplets enclosed in vesicle (e.g. oil droplets)

Endocytosis (bulk flow)

Part of the plasma membrane forms around a particle to form a vesicle, which moves into the cytosol

Exocytosis (bulk flow)

Vesicles within the cytosol fuse with the plasma membrane and vesicle contents are released from the cell