bio - module 3

Plasma Membrane

The boundary that separates the living cell from its nonliving surroundings.

Selective Permeability

The property of the plasma membrane that allows some substances to cross it more easily than others.

Fluid Mosaic Model

The concept that cellular membranes are fluid mosaics of lipids and proteins.

Phospholipids

The most abundant lipid in the plasma membrane, forming a phospholipid layer.

Amphipathic Molecules

Molecules, such as phospholipids, that have both hydrophobic and hydrophilic regions.

Fluidity of Membranes

The ability of phospholipids in the plasma membrane to move within the bilayer.

Transmembrane Proteins

Integral proteins that span the membrane.

Membrane Proteins and Their Functions

Proteins embedded in the lipid bilayer that determine most of the membrane's specific functions.

Passive Transport

Movement of substances across a membrane with no energy investment.

Diffusion

The tendency for molecules to spread out evenly into the available space.

Osmosis

The diffusion of water across a selectively permeable membrane.

Water diffuses across a membrane from the region of lower solute to the region of higher solute concentration

Tonicity

The ability of a solution to cause a cell to gain or lose water.

Facilitated Diffusion

Passive transport aided by proteins that speed the movement of molecules across the plasma membrane.

Active Transport

The movement of substances against their concentration gradient, requiring energy.

Sodium-Potassium Pump

One of the most important active transport systems in animal cells.

Cotransport

Coupled transport by a membrane protein, where the active transport of a solute indirectly drives the transport of another solute.

Primary Active Transport

Active transport that directly derives energy from the breakdown of ATP.

Secondary Active Transport

Active transport that uses an electrochemical gradient created by primary active transport.

Exocytosis

The active process of moving materials from within a cell to the exterior of the cell.

Endocytosis

The active cellular process in which substances are brought into the cell.

isotonic solution

solute concentration is the same as the inside of the cell; no net water movement across the plasma membrane

hypertonic solution

solute concentration is greater than that inside the cell; cell loses water

hypotonic solution

solute concentration is less than that inside the cell; cell gains water

uniport

movement of one molecule independent of the other molecules

symport

movement of two molecules in the same direction through a protein channel

antiport

movement of two molecules in the opposite direction through a protein channel

three types of endocytosis

• phagocytosis

• pinocytosis

• receptor-mediated endocytosis

phagocytosis (cell eating)

cell engulfs particle in a vacuole

pinocytosis (cell drinking)

cell creates vesicle around fluid

receptor-mediated endocytosis

binding of ligands to receptors triggers vesicle formation

membrane proteins functions

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and ECM