B2.1 Membranes and Membrane Transport Vocabulary

A set of 50 vocabulary flashcards covering cell membrane structure, passive and active transport, membrane fluidity, and cellular junctions based on lecture notes.

Davson-Danielli Model

An early membrane model, also known as the sandwich model, proposing that membranes consist of a phospholipid bilayer covered on both the interior and exterior surfaces by thin layers of proteins.

Singer-Nicolson Model

A cell membrane model proposed in 1972 stating that proteins are inserted into the phospholipid bilayer, forming a mosaic floating within a fluid lipid bilayer.

Fluid Mosaic Model

The currently accepted model of cellular membrane structure, describing a flexible phospholipid bilayer containing a dynamic mosaic of embedded and peripheral proteins.

Phospholipid Bilayer

The structural foundation of cell membranes composed of two layers of phospholipids, arranged with hydrophobic fatty acid tails facing inward and polar hydrophilic phosphate heads facing the exterior aqueous environment.

Amphipathic Molecules

Molecules containing both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions, such as phospholipids.

Simple Diffusion

The passive movement of small, uncharged, or non-polar molecules directly through the phospholipid bilayer from a region of higher concentration to a region of lower concentration.

Integral Proteins

Membrane proteins that are embedded directly within the hydrophobic core of the phospholipid bilayer.

Peripheral Proteins

Membrane proteins attached to the inner or outer surface of the cell membrane and not embedded within the hydrophobic region of the lipid bilayer.

Hormone-Binding Proteins

Membrane proteins with specific exterior binding sites that fit designated hormones, undergoing shape changes upon binding to relay signals to the cell interior.

Immobilized Membrane Enzymes

Membrane proteins located on the interior or exterior membrane surfaces that catalyze specific chemical reactions, often organized sequentially into metabolic pathways.

Cell Adhesion Proteins

Membrane proteins that form temporary or permanent structural connections, known as cell junctions, between neighboring cells.

Cell-to-Cell Communication Proteins

Membrane proteins, frequently conjugated with carbohydrate molecules, that function as identification labels for recognizing self versus non-self cells and transmitting extracellular signals.

Channel Proteins

Integral membrane proteins containing hydrophilic pores that provide passageways for specific water-soluble substances to pass passively across the membrane.

Protein Pumps

Specialized integral membrane proteins in active transport that move substances across the cell membrane against a concentration gradient by changing shape using energy from $\text{ATP}$.

Passive Transport

The cellular transport of substances along or down a concentration gradient (from high to low concentration) without requiring cellular energy ($\text{ATP}$).

Active Transport

The cellular movement of substances against or up a concentration gradient (from low to high concentration) requiring energy expenditure in the form of $\text{ATP}$.

Osmosis

The passive movement of water molecules across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Hypertonic Solution

A solution with a higher solute concentration relative to another solution, causing net water movement out of cells placed within it.

Hypotonic Solution

A solution with a lower solute concentration relative to another solution, causing net water movement into cells placed within it.

Isotonic Solution

A solution having an equal solute concentration relative to the cell interior, resulting in no net movement of water across the plasma membrane.

Aquaporins

Specialized integral membrane protein channels that allow water molecules to pass rapidly across the lipid bilayer.

Facilitated Diffusion

The passive transport of specific polar or charged molecules across a membrane down their concentration gradient via carrier or channel proteins without energy expenditure.

Carrier Proteins

Integral membrane proteins that bind specific molecules or ions and undergo conformational changes to transport them across the lipid bilayer.

Gated Ion Channels

Pore-forming channel proteins that open or close in response to specific chemical, electrical, or mechanical stimuli.

Selectively Permeable Membrane

A property of biological membranes allowing only specific substances to pass across based on factors like size, charge, and the availability of transport proteins.

Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ Pump)

An exchange transporter protein that uses energy from one $\text{ATP}$ molecule to actively transport three $\text{Na}^+$ ions out of the cell and two $\text{K}^+$ ions into the cell.

Resting Membrane Potential (RMP)

The electrical potential difference across the plasma membrane of a cell at rest, established and maintained primarily by the active transport of the $\text{Na}^+/\text{K}^+$ pump.

Glycolipids

Phospholipids in the plasma membrane attached to carbohydrate chains facing the extracellular space, contributing to cell recognition and adhesion.

Glycoproteins

Membrane proteins attached to carbohydrate chains on the extracellular surface, involved in cell-to-cell recognition, adhesion, and signal reception.

Glycocalyx

A thin sugar coat on the extracellular surface of animal, bacterial, fungal, or plant cells formed by the carbohydrate chains of membrane glycoproteins and glycolipids.

Cholesterol

A steroid lipid found in animal cell membranes that regulates membrane fluidity across temperature variations by interacting with phospholipid hydrocarbon tails.

Unsaturated Fatty Acids

Fatty acid tails containing double carbon bonds that create kinks, preventing tight molecular packing and maintaining membrane fluidity at lower temperatures.

Saturated Fatty Acids

Fatty acid tails without double carbon bonds that pack densely together, increasing membrane stability and density at higher temperatures.

Fatty Acid Desaturases

Bacterial enzymes that introduce double bonds into fatty acid hydrocarbon tails to preserve membrane fluidity during cold temperature exposure.

Endocytosis

An active vesicular transport process in which a portion of the plasma membrane invaginates and pinches off to enclose extracellular materials inside a vesicle.

Exocytosis

An active vesicular transport process in which intracellular vesicles fuse with the plasma membrane to release their contents into the extracellular space.

Pinocytosis

A form of endocytosis involving the non-specific internalization of extracellular liquids into small intracellular vesicles.

Phagocytosis

A form of endocytosis involving the engulfment of large solid particles, cellular debris, or foreign organisms into a food vacuole.

Receptor-Mediated Endocytosis

A selective form of endocytosis in which target molecules bind to specific membrane receptors before the membrane pinches inward to form a coated vesicle.

Endomembrane System

A cellular membrane network including the rough endoplasmic reticulum and Golgi apparatus that synthesizes, modifies, packages, and transports proteins for exocytosis.

Ligand-Gated Channels

Gated ion channels that open or close in response to the binding of a specific chemical signal molecule, such as a neurotransmitter.

Voltage-Gated Channels

Gated ion channels that open or close in response to changes in the electrical membrane potential across the plasma membrane.

Nicotinic Acetylcholine Receptors

Neurotransmitter-gated ion channels that open upon binding acetylcholine, allowing cations such as $\text{Na}^+$, $\text{K}^+$, and $\text{Ca}^{2+}$ to pass through and alter membrane potential.

Myasthenia Gravis

An autoimmune disorder in which auto-antibodies target and destroy nicotinic acetylcholine receptors at neuromuscular junctions, causing impaired muscle contraction.

Depolarization

A change in membrane potential toward a less negative value caused by a rapid inward movement of positive ions, such as $\text{Na}^+$, through open voltage-gated channels.

Repolarization

The restoration of resting membrane potential following depolarization, driven by the efflux of positive ions such as $\text{K}^+$ through open channels.

Indirect Active Transport

A transport process (co-transport) that uses the energy released by one substance moving down its concentration gradient to drive another substance against its gradient.

Sodium-Dependent Glucose Transporter (SGLT)

A co-transporter protein (such as SGLT1 in intestines or SGLT2 in kidney nephrons) that uses the favorable $\text{Na}^+$ influx gradient to move glucose into cells against its concentration gradient.

Cell-Adhesion Molecules (CAMs)

Specialized surface proteins that facilitate binding between adjacent cells or between cells and the extracellular matrix.

Desmosomes

Anchoring cell junctions formed by linker proteins and intermediate filaments that bind adjacent cells into strong, flexible sheets in tissues subjected to mechanical stress.