Structure and Permeability of the Plasma Membrane

Vocabulary flashcards covering the components, structure, and transport properties of the plasma membrane according to the fluid mosaic model.

Plasma Membrane

The semi-permeable boundary of a cell that regulates the movement of substances into and out of the cell to maintain living processes.

Fluid Mosaic Model

The structural model of the plasma membrane consisting of protein molecules floating within a phospholipid bilayer, forming a mosaic pattern that changes frequently.

Phospholipid Molecule

A primary membrane component consisting of a polar hydrophilic head and a nonpolar hydrophobic tail.

Hydrophilic Head

The polar, water-attracted portion of a phospholipid molecule; the outer layer heads face the extracellular fluid, while the inner layer heads face the cytoplasm.

Hydrophobic Tail

The nonpolar, water-repelling portion of a phospholipid molecule; the tails of the two bilayer layers face toward each other.

Channel Proteins

Protein molecules embedded within the plasma membrane that contain channels or canals to allow substances to cross.

Carrier Proteins

Membrane proteins that function as carriers to transport large molecules, such as glucose, amino acids, and vitamin C, across the plasma membrane.

Pore Protein

A membrane protein that allows small and water-soluble molecules, such as ions, to pass across the plasma membrane through passive transport.

Glycoprotein

A membrane molecule formed by a combination of proteins and carbohydrate chains (polysaccharides) that acts as hormone receptors (such as for insulin), stabilizes the membrane via hydrogen bonds with water, and acts as antigens for cell-cell recognition.

Glycolipid

A membrane molecule formed by a combination of lipids and carbohydrate chains (polysaccharides) that serves in cell-cell recognition, acts as hormone receptors, and helps stabilize the membrane with water.

Cholesterol

Molecules dispersed between phospholipid molecules that strengthen the bilayer, making it more flexible and less permeable to water-soluble substances such as ions.

Semi-Permeable Membrane

A membrane characteristic of the plasma membrane that allows only certain molecules or ions to pass through it by simple diffusion.

Factors Determining Membrane Passage

The three common factors that determine whether a molecule can cross the plasma membrane: molecule size, polar molecule properties, and ionic charge.

Lipid-Soluble Substances

Non-polar molecules that can dissolve in the lipid bilayer to cross the membrane, including vitamins A, D, E, K, steroid compounds, fatty acids, and glycerol.

Lipid-Insoluble Substances

Substances that cannot dissolve in the lipid bilayer, categorized into small molecules/ions (water, oxygen, carbon dioxide, $K^+$, $Na^+$, $Ca^{2+}$, $Mg^{2+}$) and large molecules (glucose and amino acids).

Simple Diffusion

A type of passive transport involving the movement of molecules or ions from an area of high concentration down their gradient across the plasma membrane.