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Biological Membranes

Enclose cytoplasm and organelles in cells.

Cystic Fibrosis

Genetic disease affecting chloride ion transport.

Phospholipid Bilayer

Framework of membranes with hydrophobic and hydrophilic regions.

Amphipathic Molecules

Molecules with both hydrophobic and hydrophilic parts.

Fluid-Mosaic Model

Membrane structure with lipids and proteins in motion.

Transmembrane Proteins

Proteins embedded within the phospholipid bilayer.

Lipid-Anchored Proteins

Proteins covalently attached to lipid molecules.

Peripheral Membrane Proteins

Proteins bound to membrane surfaces noncovalently.

Membrane Fluidity

Ability of molecules to move within the membrane.

Semifluid Membranes

Membranes where lipids can move laterally.

Flippase

Enzyme that transports lipids between membrane leaflets.

Alpha-Helices

Common structure in transmembrane protein segments.

Gene Encoding Transmembrane Proteins

20-30% of genes encode these proteins.

Asymmetrical Leaflets

Different compositions in the two membrane bilayer halves.

Hydrophobic Region

Part of phospholipid facing inward, away from water.

Hydrophilic Region

Part of phospholipid facing outward, towards water.

Membrane Proteins

Proteins that perform various functions in membranes.

Lateral Movement

Movement of lipids within the same membrane leaflet.

Flip-Flop Movement

Rare lipid movement between membrane leaflets.

Chloride Ion Transport

Process disrupted in cystic fibrosis patients.

Dynamic Structures

Membranes involved in vital cellular activities.

Medical Importance of Membranes

Membranes are crucial for understanding diseases.

Lipid rafts

Groups of lipids floating together in membranes.

Cholesterol concentration

High levels found in lipid rafts.

Fluidity factors

Length of phospholipid tails and double bonds.

Phospholipid tail length

Ranges from 14 to 24 carbons.

Unsaturated lipids

Contain double bonds, increasing membrane fluidity.

Temperature effects

Fluidity varies with temperature changes.

Optimal fluidity

Essential for cell function, growth, and division.

Membrane protein movement

Proteins can rotate and move laterally.

Flip-flop movement

Transmembrane proteins do not flip-flop.

Frye and Edidin experiment

Demonstrated lateral movement of membrane proteins.

Mouse-human cell fusion

Used to study protein movement at different temperatures.

Label movement at 37°C

Fluorescent label spreads across fused cells.

Integral membrane protein movement

10 to 70% may be restricted.

Cytoskeleton attachment

Restricts lateral movement of membrane proteins.

Extracellular matrix

Proteins outside the cell may restrict protein movement.

Lipid synthesis location

Occurs in the smooth endoplasmic reticulum.

Fatty acid building blocks

Made from enzymes in cytosol or food.

Lipid transfer mechanisms

Lipids diffuse or are transported via vesicles.

Lipid exchange proteins

Extract lipids for insertion into other membranes.

Transmembrane protein synthesis

Directed to ER membrane via signal sequence.

Hydrophobic amino acids

Form alpha helices in transmembrane segments.

Vesicle transport

Transfers proteins to Golgi, lysosomes, or plasma membrane.

Glycosylation

Covalent attachment of carbohydrates to proteins/lipids.

Glycolipid

Carbohydrate attached to a lipid molecule.

Glycoprotein

Carbohydrate attached to a protein molecule.

Recognition signals

Molecules that identify cells to other proteins.

N-linked Glycosylation

Carbohydrate attachment to asparagine nitrogen.

O-linked Glycosylation

Carbohydrate attachment to serine or threonine oxygen.

Golgi apparatus

Organelle where O-linked glycosylation occurs.

Membrane transport

Movement of ions/molecules across biological membranes.

Selectively permeable

Membrane allows some substances to pass, not others.

Passive transport

Movement without energy, down the concentration gradient.

Simple diffusion

Substance moves directly through phospholipid bilayer.

Facilitated diffusion

Transport protein aids solute diffusion across membrane.

Active transport

Movement against concentration gradient, requires energy.

Phospholipid bilayer

Barrier to hydrophilic molecules due to hydrophobic interior.

Solutes

Ions/molecules dissolved in a solvent like water.

Relative permeability

Ability of substances to pass through membranes.

Isotonic solution

Equal solute concentrations on both membrane sides.

Hypertonic solution

Higher solute concentration on one membrane side.

Hypotonic solution

Lower solute concentration on one membrane side.

Osmosis

Water movement from high to low concentration.

Crenation

Cell shrinkage in a hypertonic solution.

Osmotic lysis

Cell swelling and bursting in a hypotonic solution.

Plasmolysis

Plasma membrane detaches from cell wall.

Osmosis

Movement of water across a semipermeable membrane.

Hypotonic environment

Lower solute concentration outside the cell.

Contractile vacuoles

Organelles that expel excess water from cells.

Transport proteins

Proteins facilitating ion and molecule movement across membranes.

Channels

Open passageways for facilitated diffusion of substances.

Gated channels

Channels that open or close in response to ligands.

Ligands

Small molecules that bind to gated channels.

Aquaporin

Channel protein allowing rapid water transport in cells.

CHIP28

Original name for aquaporin, identified by Peter Agre.

Transporters

Proteins that change shape to move solutes across membranes.

Uniporter

Transporter for a single molecule or ion.

Symporter

Transports two or more molecules in the same direction.

Antiporter

Transports two or more molecules in opposite directions.

Active transport

Movement against concentration gradient requiring energy.

Primary active transport

Direct use of energy to move solutes.

Secondary active transport

Uses existing gradients to drive solute transport.

Electrogenic pump

Exports net positive charge, maintaining electrochemical gradients.

Ion pumps

Transport ions against gradients using ATP energy.

Exocytosis

Process of expelling materials from a cell via vesicles.

Endocytosis

Process of engulfing materials into a cell via vesicles.

Vesicles

Membrane-bound sacs used for transporting substances.

Electrochemical gradients

Differences in ion concentration and charge across membranes.

Endocytosis

Process where cells internalize substances via vesicles.

Receptor-mediated endocytosis

Specific receptors bind cargo for internalization.

Pinocytosis

Internalization of extracellular fluid via vesicles.

Phagocytosis

Engulfing large particles like bacteria by cells.

Plasma membrane

Phospholipid bilayer surrounding the cell.

Vesicle

Membrane-bound sac transporting substances within cells.

Glycoprotein

Protein with carbohydrate chains attached.

Glycolipid

Lipid with carbohydrate chains attached.

Peripheral membrane proteins

Proteins loosely attached to the membrane surface.

Transmembrane proteins

Proteins spanning the entire membrane structure.

Phospholipid bilayer

Two-layered structure forming cell membranes.