Lecture 2: Cell Membrane and Cell Transport

Vocabulary practice flashcards generated from the Anatomy & Physiology lecture on cell membrane structure and cellular transport mechanisms.

Cell Theory

The foundational biological concept stating that the cell is the smallest unit of life, all organisms are comprised of at least one cell, and cells arise only from pre-existing cells.

Plasma Membrane

A flexible outer boundary that acts as a selectively permeable barrier separating intracellular fluid (ICF) from extracellular fluid (ECF).

Interstitial Fluid

An extracellular fluid that bathes most cells in the body.

Blood Plasma

The intravascular extracellular fluid component of the circulatory system.

Extracellular Matrix

A substance external to cells that acts as glue to hold cells together.

Fluid Mosaic Model

A model describing the plasma membrane as a thin dynamic fluid structure composed of a phospholipid bilayer, cholesterol, floating embedded proteins, and carbohydrates.

Phospholipid

The primary lipid component of the plasma membrane, containing a polar, hydrophilic phosphate head and two nonpolar, hydrophobic fatty acid tails.

Cholesterol

A membrane lipid making up $20\%$ of membrane lipid content that is embedded between phospholipid tails to increase stiffness and lower fluidity.

Integral Proteins

Proteins inserted into the lipid bilayer (mostly transmembrane) with hydrophobic regions interacting with lipid tails and hydrophilic regions interacting with intracellular or extracellular fluids.

Peripheral Proteins

Proteins loosely attached to integral proteins or membrane surfaces that function as enzymes, motor proteins, or cell-to-cell connections.

Glycocalyx

A carbohydrate coating on the cell surface consisting of glycolipids and glycoproteins that acts as specific biological identification tags.

Passive Transport

Membrane transport processes that require no cellular energy ($\text{ATP}$) input, driven by intrinsic kinetic energy down a concentration gradient.

Diffusion

The natural movement of molecules from an area of higher concentration to an area of lower concentration down a concentration gradient.

Simple Diffusion

Unassisted movement of nonpolar, lipid-soluble (hydrophobic) substances directly through the phospholipid bilayer.

Facilitated Diffusion

Passive membrane transport of hydrophobic or polar molecules using carrier or channel proteins down their concentration gradient.

Leakage Channels

Transmembrane protein channels involved in channel-mediated facilitated diffusion that remain open continuously.

Gated Channels

Transmembrane protein channels controlled by chemical or electrical signals.

Osmosis

The passive movement of water across a selectively permeable membrane through the lipid bilayer or aquaporins.

Aquaporins

Transmembrane protein channels that specifically facilitate the passage of water molecules across the cell membrane.

Osmolarity

The total concentration of all solute particles in a solution, expressed in osmoles per liter ($\text{osmol/L}$).

Hydrostatic Pressure

The back pressure exerted by water against the cell wall or membrane.

Osmotic Pressure

The tendency of water to move into a cell by osmosis.

Tonicity

The ability of a solution to change the shape or plasma membrane tension of cells by altering internal water volume.

Isotonic Solution

A solution having the same osmolarity as inside the cell, resulting in unchanged cell volume.

Hypertonic Solution

A solution having a higher osmolarity than inside the cell, causing net water outflow and cell shrinking.

Crenation

The shrinking of a cell resulting from placement in a hypertonic solution.

Hypotonic Solution

A solution having a lower osmolarity than inside the cell, causing net water inflow and cell swelling.

Lysing

The bursting of a cell caused by excessive water entry in a hypotonic solution.

Active Transport

Membrane transport requiring energy ($\text{ATP}$) to move solutes across a plasma membrane against their concentration gradient.

Primary Active Transport

Active transport process where energy comes directly from the hydrolysis of $\text{ATP}$ by transport pump proteins.

Sodium-Potassium Pump

A primary active transport enzyme ($\text{Na}^+\text{-K}^+\text{ ATPase}$) that pumps $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell per $\text{ATP}$ molecule used.

Secondary Active Transport

Active transport process (cotransport) driven indirectly by energy stored in ion concentration gradients established by primary active transport.

Symporters

Cotransport proteins that transport two different substances across the membrane in the same direction.

Antiporters

Cotransport proteins that transport one substance into the cell while transporting a different substance out.

Vesicular Transport

The transport of large substances or bulk materials across cellular membranes in bubble-like membranous sacs called vesicles.

Transcytosis

A vesicular transport process moving substances into, across, and then out of the cell.

Phagocytosis

A form of endocytosis ('cell eating') where pseudopods form and engulf solid particles into a phagosome.

Pinocytosis

A non-specific form of endocytosis ('cell drinking' or fluid-phase endocytosis) where the membrane infolds to sample extracellular fluid and solutes.

Receptor-Mediated Endocytosis

A selective endocytosis process where extracellular target molecules bind to specific membrane receptors before internalization.

Exocytosis

A vesicular transport process where secretory vesicles fuse with the plasma membrane to eject contents out of the cell.

v-SNARE

A vesicle surface protein that recognizes and binds to target t-SNARE proteins on the plasma membrane to trigger exocytosis.

t-SNARE

A plasma membrane target protein that binds with v-SNAREs on secretory vesicles to facilitate membrane fusion.