Cell Membrane Structure and Transport

Vocabulary flashcards covering chapter topics on plasma membrane structure, fluid mosaic model, permeability, solution chemistry, and cellular transport mechanisms.

Plasma membrane

The outer boundary of all cells that manages what enters and exits, receives chemical signals, and allows adherence to neighboring cells and the extracellular matrix.

Fluid mosaic model

A model describing the plasma membrane as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that move laterally along the membrane without changing sides.

Amphipathic

Refers to a molecule that possesses both a hydrophilic (water-attracting) region and a hydrophobic (water-repelling) region on the same molecule.

Phospholipids

The main structural component of the cell membrane, consisting of a hydrophilic head made of glycerol and phosphate and two hydrophobic fatty acid tails.

Integral membrane protein

A protein integrated into the inner hydrophobic portion of the phospholipid bilayer, possessing both hydrophobic and hydrophilic regions.

Transmembrane protein

A type of integral protein that passes completely through the phospholipid bilayer from one side to the other.

Peripheral protein

A membrane protein located only on the outer or inner surface of the phospholipid bilayer that does not cross the entire layer.

Glycoprotein

A carbohydrate bound to a protein situated exclusively on the exterior surface of the plasma membrane, involved in cell-to-cell recognition and binding.

Glycolipid

A carbohydrate bound to a lipid located exclusively on the exterior surface of the plasma membrane.

Cholesterol (in membrane)

A lipid located within the fatty acid layer of the membrane that acts as a fluidity buffer, keeping the membrane fluid in cold temperatures and preventing it from becoming too fluid in hot temperatures.

Selectively permeable

A property of the plasma membrane that allows certain substances to pass through while preventing others from crossing.

Permeate

Refers to molecules that are capable of crossing the phospholipid bilayer directly, such as gases ($N_2$, $O_2$, $CO_2$) and small polar molecules.

Impermeable

Refers to molecules that cannot cross the phospholipid bilayer directly, such as large polar molecules (glucose) and electrically charged ions (sodium, potassium, calcium, hydrogen).

Solute

A dissolved substance in a solution, such as sodium chloride.

Solvent

A liquid capable of dissolving a solute, such as water.

Molarity ($M$)

A measure of concentration defined as the number of moles of solute contained in $1\,\text{liter}$ of solution.

Avogadro's number

The standard number of molecules in one mole of a substance, defined as $6.02 \times 10^{23}$ molecules.

Passive transport

The movement of substances across a cell membrane along a concentration gradient without requiring cellular energy.

Active transport

The movement of substances across a cell membrane that requires the expenditure of cellular energy, usually supplied by ATP.

Adenosine triphosphate (ATP)

The primary energy storage molecule in cells used to supply energy for active cellular transport and other energetic processes.

Simple diffusion

The unassisted movement of a substance from an area of higher concentration to an area of lower concentration directly across a lipid bilayer until equilibrium is reached.