Chapter 3: The Plasma Membrane and Membrane Potential

Flashcards covering the structure, protein functions, and transport mechanisms of the plasma membrane, as well as the principles of membrane potential as discussed in Chapter 3.

Plasma Membrane

An extremely thin layer of lipids and protein that forms the outer boundary of every cell, serving as a mechanical barrier and controlling the movement of molecules between the cell and its environment.

Fluid Mosaic Model

A description of the membrane structure referring to the fluid movement of the lipid bilayer and the addition of a protein mosaic.

Cholesterol

Molecules tucked between phospholipid molecules that contribute to the stability of the cell membrane.

Integral Proteins

Membrane proteins that are firmly inserted into and extend across the lipid bilayer.

Peripheral Proteins

Membrane proteins that lie loosely on the inner and outer surfaces of the cell membrane.

Channels

Integral proteins that span the membrane and allow the passage of small, water-soluble molecules such as ions.

Carrier Proteins

Integral proteins involved in carrier-mediated transport that are specific for larger molecules.

Docking Proteins

Proteins located on the inner surface of the membrane where secretory vesicles bind prior to exocytosis.

Receptors

Proteins that bind with specific molecules in the cell's environment, such as hormones, triggering responses in specific cells.

Cell Adhesion Molecules (CAMs)

Proteins that act as "velcro" connections between adjacent cells.

Glycoproteins

Peripheral proteins attached to carbohydrates used for cell recognition, including "self" recognition for the immune response.

Extracellular Matrix

A biological "glue" holding cells together, composed of protein fibers such as collagen, elastin, and fibronectin.

Desmosomes

Specialized cell junctions that act like "spot rivets" to anchor adjacent nontouching cells; they are abundant in tissues subject to stretching.

Tight Junctions

Impermeable junctions that firmly bond adjacent cells and seal off the passageway between them, primarily found in epithelial tissue.

Gap Junctions

Communicating junctions formed by small connecting tunnels called connexons that link the cytosol of adjacent cells.

Diffusion

The passive movement of molecules from an area of higher concentration to an area of lower concentration.

Fick’s Law of Diffusion

The law stating that the rate of diffusion is influenced by the magnitude of the concentration gradient, membrane permeability, surface area, molecular weight, and distance.

Osmosis

The net diffusion of water down its own concentration gradient.

Isotonic Solution

A solution with a concentration of nonpenetrating solutes equal to that of normal body cells ($0.9\%\,NaCl$), resulting in no change in cell volume.

Hypotonic Solution

A solution with a lower concentration of nonpenetrating solutes than normal body cells, causing cells to gain water and swell.

Hypertonic Solution

A solution with a higher concentration of nonpenetrating solutes than normal body cells, causing cells to lose water and shrink.

Filtration

The process where water and solutes are forced through a membrane by hydrostatic pressure, such as blood being filtered through the kidney capillaries.

Facilitated Diffusion

A passive transport process that uses a carrier molecule to move substances from higher to lower concentration, used by glucose to enter cells.

Active Transport

The movement of a substance against its concentration gradient requiring a carrier molecule and the direct use of energy in the form of $ATP$.

$Na^+/K^+$ ATPase Pump

A primary active transport mechanism that pumps $3\,Na^+$ out of the cell for every $2\,K^+$ pumped in, maintaining the resting membrane potential.

Secondary Active Transport

Transport driven by an ion gradient (usually $Na^+$) established by an $ATP$-requiring primary pump, rather than using $ATP$ directly.

Endocytosis

The process of bringing large substances into the cell; categories include phagocytosis ("cell eating") and pinocytosis ("cell drinking").

Exocytosis

The process of expelling substances, such as proteins or waste, from the cell into the extracellular fluid.

Resting Membrane Potential

The electrical polarization of a cell membrane at rest, typically measured at $-70\,mV$, resulting from the distribution of ions like $Na^+$, $K^+$, and intracellular anions ($A^-$).

Electrogenic Pump

A term for the $Na^+/K^+$ pump because it contributes to the membrane potential by pumping more positive charges out than in (ratio of $3\text{:}2$).