Membrane Structure and Function

Vocabulary flashcards covering cellular membrane structure, the fluid mosaic model, membrane fluidity, transport mechanisms (passive, active, osmosis, bulk transport), and electrochemical gradients based on Chapter 7 BIO-151.

Davson-Danielli Model

A sandwich model of cell membrane structure proposed in $1935$ by Hugh Davson and James Danielli, stating that the phospholipid bilayer is positioned between two outer layers of globular proteins.

Fluid Mosaic Model

A model of membrane structure proposed in $1972$ by J. Singer and G. Nicolson, describing the membrane as a fluid phospholipid bilayer embedded and attached with a mosaic of proteins, with only hydrophilic regions exposed to water.

Amphipathic Molecule

A molecule that contains both hydrophobic (water-repelling) and hydrophilic (water-attracting) regions, characteristic of phospholipids and membrane proteins.

Membrane Fluidity

The ability of membrane lipids and proteins to shift laterally; phospholipids move laterally approximately $10^7$ times per second and flip-flop about once per month, with fluidity enhanced by unsaturated hydrocarbon tails with kinks and modulated by cholesterol.

Glycoprotein

A membrane surface component consisting of a carbohydrate (sugar) covalently bonded to a protein, varying between species and individual cells to facilitate cell recognition.

Glycolipid

A membrane surface molecule formed by a carbohydrate (sugar) covalently bonded directly to a lipid.

Integral Proteins

Amphipathic transmembrane proteins that penetrate into and often span the hydrophobic core of the lipid bilayer.

Peripheral Proteins

Proteins that are not embedded in the lipid bilayer but are loosely bound to the exterior or interior surface of the membrane.

Selective Permeability

A vital property of the plasma membrane allowing non-polar, small molecules (such as hydrocarbons, $O_2$, and $CO_2$) to pass easily, while restricting the passage of ions and polar molecules.

Aquaporins

Channel proteins that facilitate the rapid passage and diffusion of water ($H_2O$) molecules through the plasma membrane.

Passive Transport

The net diffusion of a substance across a biological membrane down its concentration gradient (from high to low concentration) without any expenditure of cellular energy.

Channel Proteins

Transport proteins with a hydrophilic interior tunnel that specific molecules or ions use as a passage through the membrane.

Carrier Proteins

Transport proteins that bind to specific passenger molecules and undergo a change in shape to shuttle them across the membrane.

Osmosis

The passive transport of water across a selectively permeable membrane from an area of lower solute concentration (hypotonic) to an area of higher solute concentration (hypertonic) until concentrations equalize.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water ($H_2O$).

Isotonic Solution

A solution whose solute concentration is equal to that inside the cell, resulting in no net movement of water across the membrane.

Hypertonic Solution

A solution with a higher solute concentration than the inside of the cell, causing water to leave the cell and leading to shriveling in animal cells and plasmolysis in plant cells.

Hypotonic Solution

A solution with a lower solute concentration than the inside of the cell, causing water to enter the cell and leading to lysis in animal cells or normal turgidity in plant cells.

Osmoregulation

The biological control of water balance in organisms, exemplified by the contractile vacuole in pond-dwelling Paramecium.

Active Transport

The energy-requiring ($\text{ATP}$) movement of a solute across a cellular membrane against its concentration gradient (from low to high concentration) utilizing specific carrier proteins.

Sodium-Potassium Pump

The major electrogenic active transport pump in animal cells that hydrolyzes $\text{ATP}$ to pump $Na^+$ out of the cell and $K^+$ into the cell against their respective concentration gradients.

Membrane Potential

The voltage difference across a cell membrane created by the differential distribution of positive and negative ions between the cytoplasm and extracellular fluid.

Electrochemical Gradient

The dual driving force for ion diffusion across a membrane, composed of a chemical force (the ion's concentration gradient) and an electrical force (the effect of the membrane potential).

Electrogenic Pump

A transport protein that generates voltage across a membrane, such as the sodium-potassium pump in animals or the proton pump in plants, fungi, and bacteria.

Proton Pump

The primary electrogenic pump in plants, fungi, and bacteria that uses $\text{ATP}$ to actively transport hydrogen ions ($H^+$) out of the cell.

Cotransport

A transport mechanism in which the active pumping of $1$ substance creates a gradient that drives the simultaneous transport of a second substance against its own concentration gradient as the first diffuses back in.

Exocytosis

The cellular process of exporting large molecules or secretions out of the cell through the fusion of intracellular vesicles with the plasma membrane.

Endocytosis

The cellular uptake of biological matter and fluid by pinching in the plasma membrane to form new intracellular vesicles.

Phagocytosis

A type of endocytosis referred to as 'cellular eating,' where a cell uses pseudopodia to engulf large particles or microbes into a membrane-bound sac called a food vacuole or phagosome.

Pinocytosis

A type of endocytosis referred to as 'cellular drinking,' in which the cell invaginates its membrane to take in non-specific droplets of extracellular fluid into small vesicles.

Receptor-Mediated Endocytosis

A specialized, highly selective form of endocytosis triggered when extracellular ligands bind specifically to receptor proteins located in coated pits of the plasma membrane.

Ligand

Any molecule that binds specifically and reversibly to a receptor site on another molecule.