Cell Membranes and Bilayers

Flashcards covering key vocabulary related to cell membrane structure, lipid bilayer properties, membrane fluidity, and substance movement across membranes, including diffusion and osmosis.

Cell Membrane

An asymmetrical lipid bilayer that contains proteins and may have glycolipids on its outer surface.

Asymmetrical (Cell Membrane)

Refers to the cell membrane structure where glycolipids are only present on the side facing the outside environment, not the cytoplasm.

Glycolipids

Sugar molecules located exclusively on the outside of the cell membrane, facing the external environment.

Lipid Bilayer

A selective, permeable barrier formed spontaneously by amphipathic membrane lipids, limiting movement of hydrophilic molecules and ions, and lacking proteins compared to a cell membrane.

Leaflet

Each individual row of phospholipids within a lipid bilayer.

Amphipathic

A characteristic of membrane lipids possessing both a hydrophilic (water-loving) and a hydrophobic (water-repelling) portion.

Hydrophilic

The water-interacting portion of an amphipathic molecule.

Hydrophobic

The water-repelling portion of an amphipathic molecule that tends to stick together.

Van der Waals Interaction

The attraction by which hydrophobic molecules tend to stick together, significant in lipid bilayer formation and stability.

Spontaneous Reaction

A reaction that does not require energy input to occur, often releasing energy.

Exergonic Reaction

A reaction that releases energy, often in the form of heat or light, characteristic of spontaneous processes like lipid bilayer formation, diffusion, and osmosis.

Entropy

A measure of disorder; an increase in entropy, particularly of water molecules around the lipid bilayer, contributes to spontaneous reactions.

Selective Permeability

The property of the lipid bilayer that limits the passage of certain molecules, especially hydrophilic molecules and charged ions, while allowing others to pass.

Passive Transport

The movement of small, nonpolar molecules (like oxygen, CO2, nitrogen) across a membrane without any assistance or energy input.

Flexion (Phospholipids)

The movement or bending of the fatty acid tails within an individual phospholipid molecule.

Rotation (Phospholipids)

The spinning movement of an individual phospholipid molecule around its own axis within the membrane.

Lateral Diffusion (Phospholipids)

The movement of phospholipids past each other within the same leaflet (row) of the lipid bilayer.

Transverse Diffusion (Flip-flop)

A rare movement where a phospholipid flips from one leaflet of the bilayer to the other, requiring significant energy.

Membrane Fluidity

The dynamic characteristic of the cell membrane, influenced by phospholipid movements and environmental factors, affecting its permeability.

Heat

Introducing kinetic energy into the lipid bilayer, which increases membrane fluidity and permeability.

Unsaturated Lipids

Fatty acids or lipids containing at least one carbon-carbon double bond, which creates kinks, increasing membrane fluidity and permeability by reducing Van der Waals interactions between tails.

Saturated Lipids

Fatty acids or lipids containing only carbon-carbon single bonds, resulting in straight tails that pack closely, decreasing membrane fluidity and permeability by increasing Van der Waals interactions.

Cholesterol

A chunky molecule that, when added to a membrane, reduces its permeability by filling gaps and packing lipid tails closer together.

Gradient

A difference in concentrations or a physical entity (e.g., temperature) across two sides of something.

Concentration Gradient

A difference in the concentration of solutes between two regions, often separated by a membrane.

Diffusion

The net movement of a solute from a region of high concentration to a region of low concentration, occurring spontaneously and exergonically to spread substances evenly.

Down the Gradient

Movement of a substance from a region of high concentration to a region of low concentration.

Equilibrium (Diffusion)

The state where concentrations of solutes are equal on both sides of a membrane, resulting in no net movement across it.

Osmosis

The movement of water across a selectively permeable membrane (impermeable to solutes) from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration), occurring spontaneously and exergonically.