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Membrane Structure and Function - Coggle Diagram
Membrane Structure and Function
Cellular Membranes are Fluid Mosaics
Structure of the Plasma Membrane
The membrane that separates the cell from its surroundings.
Lipids, proteins, carbohydrates.
Fluid Mosaic Model --> membrane is a mosaic of proteins bobbing in a fluid bilayer of phospholipids.
Fluidity of Membranes
Phospholipid Movement: Lateral movement (common), flip-flop (rare).
Temperature Effect:
Decreases --> membrane solidifies.
Increases --> membrane becomes more fluid.
Saturated vs. Unsaturated Fatty Acids:
Saturated --> less fluid.
Unsaturated --> more fluid.
Cholesterol's Role:
At moderate temp --> reduces fluidity.
At low temp --> prevents solidification.
Carbohydrates in the Membrane
Glycolipids / Glycoproteins: Carbohydrates covalently bonded to lipids or proteins.
Function: Cell-cell recognition ( Ex: immune response).
Differences in Membrane Lipid Composition
Definition: The lipid composition of cell membranes varies among species, and even among cell types within the same organism.
The lipid composition of the cell membrane appears to be adapted to environmental conditions in many species.
Ex: cell membranes have a high proportion of unsaturated hydrocarbon tails in fish that live in extreme cold.
Organisms living in variable temperature conditions are able to change lipid composition in response to changing temperature.
Ex: in winter wheat, the percentage of unsaturated phospholipids increase in autumn to prevent membrane solidification during winter.
Sidedness of Membranes:
Asymmetrical: Inner and outer layers differ in composition.
Built by the ER and Golgi apparatus.
Membrane Proteins and Their Function
1- Integral Proteins: penetrate the hydrophobic core. ( ex: Transmembrane proteins).
2- Peripheral proteins: are bound to the surface of the
membrane.
Cell-surface membrane proteins can carry out
several functions:
Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
Membranes in Selective Permeability
Definition: The property that allows some substances to cross more easily than others.
Permeable Substances:
Hydrophobic (nonpolar) molecules: CO2, O2, lipids: easily pass through.
Small uncharged polar molecules: H2O can pass slowly.
Ions and large polar molecules molecules: Glucose, Na+: need transport proteins.
Transport Proteins:
Channel Proteins: Provides corridors for specific molecules or ions. Ex: Aquaprorins for water.
Carrier Proteins: Bind to molecules and change shape to shuttle them.
Diffusion:
Definition: Movement of molecules from high to low concentration.
Passive process: No energy required.
Concentration Gradient: Driving force for diffusion.
Passive Transport
Definition:
Transport across membrane without energy input.
Types of Passive Transport:
Simple Diffusion: Movement directly through lipid bilayer.
Facilitated Diffusion: Movement via transport proteins.
Facilitated Diffusion Details:
Provide hydrophilic pathways (ex: ion channels)
Under shape change when transporting.
Aquaporins: Specialized water channels.
Osmosis:
Definition: Diffusion of water through a selectively permeable membrane.
Tonicity:
Isotonic: Equal solute concentration
Hypertonic: Solute concentration higher outside --> cell shrinks.
Hypotonic: Solute concentration lower outside --> cell swells.
Osmoregulation:
Definition:Control of solute concentrations and water balance.
Ex: Paramecium uses contractile vacuole.
Active Transport
Definition: Movement of solutes against concentration gradient.
Requires energy (ATP) and carrier proteins.
Types of Active Transport Proteins:
Pumps:
Sodium-Potassium pump: 3 Na+ out, 2 K+ in.
Proton Pump: Moves H+; creates membrane potential.
Membrane Potential:
Definition: Voltage across membrane.
Created by unequal of ions.
Electrochemical Gradient --> Combination of chemical and electrical forces.
Contransport:
Definition:Coupled transport using gradient of one solute to drive another.
Ex: Sucrose-H+ contransporter in plant.
Bulk Transport
Definition:Transport of large molecules or particles across membrane via vesicles.
Endocytosis (into the cell):
Phagocytosis: "Cell eating": engulfing large particles.
Pinocytosis: "Cell drinking": taking in extracellular fluid.
Receptor-mediated Endocytosis: Specific uptake using receptor proteins.
Exocytosis (out of the cell):
Definition:Vesicles fuse with membrane to release contents outside.
Ex: Secretion of neurotransmitters, hormones, or proteins.
Example Application:
Neurons: Release neurotransmitters via exocytosis.
Immune cells: Engulf pathogens via phagocytosis.