CH 7 - Membrane Structure and Function

Flashcards covering key vocabulary related to membrane structure and function based on lecture notes CH 7.

Fluid Mosaic Model

Cellular membranes are fluid mosaics of lipids and proteins.

Phospholipids

The most abundant lipids in most membranes, characterized by being amphipathic with a hydrophilic head and hydrophobic tails.

Amphipathic

Having both a hydrophilic ('water loving') region and a hydrophobic ('water fearing') region.

Hydrophilic region (head)

The 'water loving' part of a phospholipid, exposed to the aqueous environment on both sides of the membrane.

Hydrophobic region (tails)

The 'water fearing' part of a phospholipid, creating the inside of the membrane and protected from aqueous solution.

Membrane Fluidity

The property of a membrane where lipids and some proteins can shift around within its plane, held together by weaker hydrophobic interactions.

Cholesterol

A steroid found in the plasma membranes of animal cells that acts as a fluidity buffer.

Fluidity Buffer

A component, like cholesterol, that helps maintain membrane fluidity across a range of temperatures; prevents membrane from becoming too fluid or too solid.

Integral Proteins

Membrane proteins that penetrate the hydrophobic interior of the lipid bilayer.

Transmembrane Proteins

Integral proteins that span the entire membrane, fully embedded and having access to both the inside and outside of the cell.

Peripheral Proteins

Membrane proteins that are not embedded in the lipid bilayer at all, but are loosely bound to the surface of the membrane.

Transport Proteins

Membrane proteins that facilitate the movement of specific molecules or ions across the membrane.

Enzymatic Activity (membrane proteins)

A function of membrane proteins where a protein built into the membrane acts as an enzyme with an exposed active site to react with substrates.

Signal Transduction (membrane proteins)

A function where a membrane protein (receptor) binds to a chemical messenger (ligand), changes shape, and relays a message into the cell.

Cell to Cell Recognition

A function where some glycoproteins on the membrane serve as identification tags recognized by other cell's membrane proteins, often involving short-lived binding.

Intercellular Joining

A function where membrane-bound proteins of adjacent cells bind together via junctions, creating longer-lasting connections than cell-cell recognition.

Attachment to the Cytoskeleton and ECM

A function where membrane proteins are noncovalently bonded to cytoskeleton components or bound to the extracellular matrix (ECM) to coordinate cellular changes.

Ligand

A chemical messenger or signaling molecule that specifically binds to a receptor protein on the membrane.

Receptor (membrane protein)

A membrane protein with a specific binding site for a chemical messenger (ligand), involved in signal transduction.

Glycoproteins

Carbohydrates covalently bonded to proteins on the outer surface of the plasma membrane, serving as cell identification tags.

Glycolipids

Carbohydrates covalently bonded to lipids on the outer surface of the plasma membrane, serving as cell markers for cell-cell recognition.

Cell Markers

Glycolipids and glycoproteins that serve as identification tags for cell-cell recognition.

Selective Permeability

The property of a membrane that allows some substances to cross through more easily than others.

Channel Proteins

Transport proteins that provide a hydrophilic channel through the membrane for specific molecules or ions to pass.

Aquaporins

Specific channel proteins that facilitate the rapid transport of water across the membrane.

Carrier Proteins

Transport proteins that bind to specific molecules, change shape, and then release the molecule on the other side of the membrane.

Passive Transport

The diffusion of a substance across a membrane with no energy investment, driven by the concentration gradient.

Diffusion

The movement of particles in which they spread out from an area of higher concentration to an area of lower concentration to achieve equilibrium.

Concentration Gradient

A difference in the concentration of a substance across a distance or membrane, driving diffusion.

Osmosis

The diffusion of water across a selectively permeable membrane, moving from a region of higher water concentration to lower water concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water, depending on the solute concentration.

Isotonic Solution

A solution with the same solute concentration as the inside of 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 move out of the cell, leading to shriveling.

Hypotonic Solution

A solution with a lower solute concentration than the inside of the cell, causing water to move into the cell, potentially leading to swelling and lysis.

Osmoregulation

The control of solute concentrations and water balance within a cell or organism.

Turgid (cell)

A very firm cell structure in cells with cell walls, due to significant water uptake.

Flaccid (cell)

A limp cell structure in cells with cell walls, due to a lack of significant net water uptake or loss.

Plasmolysis

The process in cells with cell walls where the plasma membrane pulls away from the cell wall due to water leaving the cells, causing wilting and potential death.

Facilitated Diffusion

Passive transport aided by proteins, allowing ions and polar molecules, normally blocked by the lipid bilayer, to pass through the membrane.

Ion Channels

Channel proteins that facilitate the transport of specific ions across the membrane.

Gated Channels

Ion channels that open or close in response to a specific stimulus.

Active Transport

Movement of solutes across a membrane against their concentration gradients, requiring the input of energy, typically from ATP.

Sodium-Potassium Pump (Na+/K+ pump)

An active transport protein that pumps three Na+ ions out of the cell and two K+ ions into the cell for every ATP molecule hydrolyzed, maintaining electrochemical gradients.

Membrane Potential

A voltage difference across the plasma membrane, serving as an energy source that directs the traffic of charged substances (ions).

Electrochemical Gradient

The combined effect of an ion's chemical concentration gradient and the electrical force (membrane potential) that influences its movement across a membrane.

Proton Pump (H+)

The main electrochemical pump of plants, fungi, and bacteria, which actively transports hydrogen ions (protons) out of the cell.

Cotransport

A type of coupled transport where a membrane protein couples the 'downhill' diffusion of one solute with the 'uphill' transport of a second substance against its concentration gradient.

Exocytosis

The process of secreting molecules from the cell via the fusion of vesicles with the plasma membrane.

Endocytosis

The process of taking in molecules into the cell via the formation of new vesicles from the plasma membrane.

Phagocytosis

A type of endocytosis where a cell engulfs large particles by extending pseudopodia and packaging them into a food vacuole.

Pinocytosis

A type of endocytosis where a cell continuously takes in droplets of extracellular fluid into tiny vesicles formed by infoldings of the plasma membrane.

Receptor-Mediated Endocytosis

A type of endocytosis that takes in bulk quantities of specific solutes, which bind to receptor proteins that then cluster together and form vesicles containing the bound solutes.