Cells: The Living Units - Cellular Structure and Membrane Transport

Vocabulary flashcards covering cellular structure, generalized cell components, plasma membrane structure and proteins, cell junctions, and passive transport mechanisms including diffusion and osmosis.

Cell Theory

The foundational principle stating that the cell is the structural and functional unit of life, organismal function depends on combined cellular activities, continuity of life has a cellular basis, and biochemical functions are dictated by cell shape and subcellular structures.

Plasma Membrane

A flexible outer boundary separating intracellular fluid (ICF) from extracellular fluid (ECF) that regulates the entry and exit of substances.

Cytoplasm

The region between the plasma membrane and nucleus containing intracellular fluid and cellular organelles.

Nucleus

The cellular control center containing genetic material (DNA).

Interstitial Fluid

An extracellular body fluid in which human cells are submersed or bathed.

Extracellular Matrix

A substance found outside of cells that acts as glue to hold cells together.

Fluid Mosaic Model

A structural model depicting the plasma membrane as a flexible lipid bilayer with floating specialized membrane proteins that create constantly changing patterns.

Glycocalyx

A carbohydrate-rich layer on the outer surface of the plasma membrane composed of glycoproteins and glycolipids that functions in cell-to-cell recognition and immune identification.

Phospholipids

Membrane lipids that form $75BA$ of the lipid bilayer, consisting of polar hydrophilic phosphate heads and nonpolar hydrophobic fatty acid tails.

Glycolipids

Lipids with attached sugar groups located on the outer membrane surface, accounting for $5\%$ of membrane lipids.

Cholesterol

A membrane steroid lipid tucked between hydrophobic phospholipid tails, making up $20\%$ of membrane lipids to increase stability and stiffen the membrane.

Integral Proteins

Proteins firmly inserted into the lipid bilayer, most of which are transmembrane proteins possessing hydrophobic regions that interact with lipid tails and hydrophilic regions that interact with water.

Peripheral Proteins

Proteins loosely attached to integral proteins on the inner or outer surface of the phospholipid bilayer, functioning as enzymes, motor proteins, or cell-to-cell connections.

Tight Junctions

Impermeable cell junctions formed by the fusion of integral proteins on adjacent cells, encircling cells to prevent fluids and molecules from passing between them.

Desmosomes

Anchoring cell junctions formed by interlocking cadherin linker proteins attached to membrane plaques and reinforced by intercellular keratin filaments to prevent cell separation under mechanical tension.

Gap Junctions

Communicating cell junctions formed by transmembrane channel proteins called connexons that allow ions, simple sugars, and small molecules to pass directly from cell to cell.

Passive Transport

Membrane transport mechanisms that move substances down their concentration gradient without requiring cellular energy (ATP).

Active Transport

Membrane transport processes that require energy in the form of ATP to move substances across the plasma membrane.

Simple Diffusion

The passive movement of nonpolar, lipid-soluble substances directly through the phospholipid bilayer down their concentration gradient.

Facilitated Diffusion

The passive transport of lipid-insoluble or polar molecules across the plasma membrane with the assistance of carrier or channel proteins.

Carrier-Mediated Facilitated Diffusion

A type of passive transport in which specific polar molecules bind to transmembrane protein carriers, triggering a shape change that transports the molecule across the membrane.

Channel-Mediated Facilitated Diffusion

Passive transport through aqueous-filled transmembrane channels, allowing specific ions or water to move down their concentration gradients.

Aquaporins

Transmembrane channel proteins that facilitate the rapid transport of water molecules across the plasma membrane.

Osmosis

The diffusion of a solvent (usually water) across a selectively permeable membrane from an area of higher solvent concentration to an area of lower solvent concentration.

Osmolarity

A measure of the total concentration of solute particles in a solvent, expressed in units of $\text{osmol/L}$.

Hydrostatic Pressure

The outward pressure exerted on the cell side of a membrane caused by increased fluid volume inside the cell due to osmosis.

Osmotic Pressure

The inward pressure created by the tendency of water to be pulled into a cell containing a higher solute concentration.

Tonicity

The ability of an extracellular solution to alter a cell's internal water volume, thereby changing its shape or tone.

Isotonic Solution

A solution with the same solute and water concentration as the cell interior, maintaining normal cell shape and volume.

Hypertonic Solution

A solution with a higher concentration of nonpenetrating solutes than the cell interior, causing water to leave the cell by osmosis and resulting in cell shrinkage.

Hypotonic Solution

A solution with a lower concentration of nonpenetrating solutes than the cell interior, causing water to enter the cell by osmosis and resulting in swelling and possible bursting.

Crenation

The shrinking of cells caused by the loss of water when placed in a hypertonic solution.

Lysing

The bursting of cells caused by excessive water entry when placed in a hypotonic solution.