Biological Membranes Flashcards

Flashcards about biological membranes, their structure, function, and related processes.

Plasma Membrane

The outer boundary of a cell that controls the movement of substances in and out.

Organelles

Inner compartments within cells, also bounded by membranes.

Selective Permeability

The property of membranes that allows them to control which substances can pass through.

Membrane Components

The three major components of biological membranes: lipids, proteins, and sugars.

Lipids

Biologically important substances insoluble in water but soluble in organic solvents.

Phospholipids

A type of lipid containing glycerol linked to two fatty acid chains, phosphate, and choline.

Glycolipids

Lipids containing either glycerol or sphingosine linked to fatty acid chains and a sugar.

Cholesterol

A type of membrane lipid with a four-ring steroid structure, a short hydrocarbon side-chain, and a hydroxy group.

Amphipathic

A characteristic of membrane lipids, meaning they have both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region.

Liposomes

Sealed compartments formed by lipid bilayers in water, useful as model membranes and drug delivery systems.

Transmembrane Proteins

Membrane proteins that extend across the lipid bilayer, with hydrophobic regions embedded within the bilayer.

Integral Membrane Proteins

Proteins firmly attached to the membrane that can only be removed by treatments which disrupt the membrane.

Peripheral Membrane Proteins

Proteins weakly bound to the surface of the membrane by non-covalent interactions.

Glycoproteins

Proteins of the plasma membrane that have covalently linked sugars.

Lateral Diffusion

The rapid movement of phospholipids and proteins past each other along the membrane.

Transverse Diffusion (Flip-Flop)

The rare movement of a lipid molecule from one monolayer to the opposite one.

Phospholipid Translocators (Flippases)

Proteins that catalyze the rapid flip-flop of particular lipids across the bilayer in the endoplasmic reticulum.

Transition Temperature

The temperature at which a lipid bilayer melts from an ordered arrangement (gel state) to a disordered arrangement (liquid state).

Fluid Mosaic Model

A model depicting the membrane as a seething mass of lipids and proteins in which movements of molecules take place in two dimensions.

SDS/Polyacrylamide-Gel Electrophoresis

A technique used to visualize and measure the molecular mass of membrane proteins.

Cell Fusion

A technique to show the mobility of membrane proteins, where cells are fused and labeled with fluorescent dyes.

Fluorescence Photobleaching Recovery

A technique to measure the mobility of lipids and proteins in membranes by monitoring the recovery of fluorescence in a bleached area.

Lectins

Carbohydrate-binding proteins used to show that carbohydrates are located on only the outer surface of plasma membranes.

Endoplasmic Reticulum (ER)

The site in eukaryotic cells where membrane components are synthesized.

Flippase Enzymes

Enzymes in the ER membrane that transfer newly formed phospholipids to the opposite monolayer.

Phospholipid-Exchange Proteins

Water-soluble carrier proteins that remove phospholipids from the ER membrane and deposit them in the membranes of organelles.

Signal Recognition Particle (SRP)

A complex of protein with RNA that brings the growing protein chain and attached ribosome to the ER.

Stop-Transfer Signals

Sequences of hydrophobic amino acids within a protein chain that arrest the passage of the protein through the ER membrane.

Simple Diffusion

The process by which small hydrophobic molecules can readily cross phospholipid bilayers.

Fick's Law

Describes the rate of diffusion; proportional to the concentration difference, membrane area, and permeability coefficient.

Mediated Transport

The transport of ions, sugars, and amino acids across membranes via integral membrane proteins.

Channels

Transport proteins that form water-filled pores across the bilayer, through which inorganic ions move.

Ligand-Gated Channels

Channels that are opened by the binding of a signal molecule.

Voltage-Gated Channels

Channels that are opened by a change in membrane potential.

Carriers (Transporters)

Transport proteins that bind specific molecules or ions and transfer them across the membrane.

Uniports

Carrier proteins that transport only one solute across the membrane.

Co-transporters

Carrier proteins that transport two solutes at the same time.

Symport

A type of co-transport where two solutes are transported in the same direction.

Antiport

A type of co-transport where two solutes are transported in opposite directions.

Passive Transport (Facilitated Diffusion)

Transfer of molecules or ions across the membrane downhill, without requiring energy input.

Active Transport

Transfer of solutes across the membrane uphill, against their electrochemical gradient, requiring energy input.

ATP-Driven Pumps

Active transport processes driven by the hydrolysis of ATP.

Na+/K+-Exchanging ATPase (Sodium Pump)

An enzyme that actively pumps Na+ ions out and K+ ions into animal cells.

Secondary Active Transport

Active transport driven by ion gradients generated by another active transport system.

Exocytosis

The process by which cells secrete macromolecules by fusion of vesicles with the plasma membrane.

Endocytosis

The process by which cells take in macromolecules by enclosing them in vesicles formed from the plasma membrane.

Pinocytosis (Cell Drinking)

A type of endocytosis where fluid or small particles are taken into small vesicles.

Phagocytosis (Cell Eating)

A type of endocytosis where large particles, such as micro-organisms and cell debris, are taken into large vesicles.

Receptor-Mediated Endocytosis

A process by which specific macromolecules are taken into cells via receptors clustered in coated pits.

Clathrin

A protein that forms a lattice around coated pits, causing the formation of coated vesicles.

Low-Density Lipoproteins (LDLs)

Spherical particles that carry cholesterol in the blood.

Fat-Soluble Messengers

Hormones that are soluble in lipids and can diffuse across the plasma membrane (e.g., steroids, vitamins A and D, thyroxine).

Water-Soluble Messengers

Hormones that are soluble in water and cannot cross the plasma membrane (e.g., adrenaline, glucagon, and insulin).

GTP-Binding Proteins (G-Proteins)

Proteins that bind GTP and are involved in signal transduction across the plasma membrane.

Second Messengers

Small molecules produced in response to hormone binding that trigger a series of enzyme-catalyzed reactions (e.g., cyclic AMP).

Adenylate Cyclase

An enzyme that produces cyclic AMP from ATP.

Nerve Impulse (Action Potential)

A change in membrane potential that carries information along the axon of a nerve cell.

Synapse

The gap between the end of an axon and the next nerve cell or muscle cell.

Neurotransmitter

Molecules released into the synaptic gap by exocytosis to transmit a message to the next cell.