CELLULAR TRANSPORT SBI 3C SEPTEMBER 2010

PASSIVE TRANSPORT:  Transport that does not require energy.  Important Terms:  Dynamic equilibrium:  A state of balance where particles move in all directions at equal rates.  Selectively Permeable:  Allows only certain substances to pass through it.  Concentration gradient:  A difference in concentration between two areas  Transmembrane Protein:  A protein molecule in a membrane that spans the thickness of the phospholipid bilayer (goes all the way across the membrane)  Carrier Protein:  A transmembrane protein that facilitates the diffusion of certain substances through the membrane.

SIMPLE DIFFUSION  A movement of particles from an area of high concentration to low concentration  Process continues until dynamic equilibrium is reached and particles are spread out evenly  Examples:  Small, uncharged molecules, such as water, oxygen, carbon dioxide  Ions (small, charged molecules) and large molecules (amino acids, carbohydrates, nucleic acids, large lipids) cannot pass through easily

SIMPLE DIFFUSION

FACILITATED DIFFUSION:  Just like simple diffusion except particles are helped across the membrane by a carrier protein  Used for larger molecules that can’t fit through the membrane  Continues until dynamic equilibrium is reached  Examples:  Ions (small, charged molecules)  Large molecules (amino acids, carbohydrates, nucleic acids, large lipids)

FACILITATED DIFFUSION:

OSMOSIS  Movement of water across a selectively permeable membrane from high water concentration (low solute concentration) to low water concentration (high solute concentration)  Note: only the water molecules (open circles) move not the solute molecules (closed circles)

ISOTONIC SOLUTION  Equal concentration of solute and water inside and outside  Everything is balanced and nothing moves

HYPOTONIC SOLUTION  Lower concentration of solute outside the cell  Higher concentration of water outside the cell  Water enters the cell  Cell swells and bursts

HYPERTONIC SOLUTION  Higher concentration of solute outside of cell  Lower concentration of water outside of cell  Water leaves the cell  Cell shrivels up

ACTIVE TRANSPORT  Special carriers use energy (ATP) to move chemicals across a membrane  Goes against the concentration gradient  Keeps going even after dynamic equilibrium is reached

SODIUM-POTASSIUM PUMP  An active transport mechanisms that pumps sodium and potassium ions into and out of the cell  Required so that nerve and muscle cells function properly

BULK TRANSPORT  The movement of large quantities of materials into or out of a cell  Endocytosis:  A form of bulk transport used to bring large amounts of materials into the cell from the outside  Two forms:  Phagocytosis  Pinocytosis

PHAGOCYTOSIS:  Also known as cell eating  The bulk transport of solids into the cell

PINOCYTOSIS:  Also known as cell drinking  The bulk transport of liquid into the cell

EXOCYTOSIS:  The movement of large amounts of material out of a cell

FACTORS AFFECTING RATE OF DIFFUSION:  Rate of diffusion depends on temperature and concentration of solute molecules in solution