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Membrane Structure & Function - Coggle Diagram
Membrane Structure & Function
Fluid Mosaic Model
Definition: Plasma membrane is fluid and made of a mosaic of proteins and lipids
Phospholipid Bilayer
Amphipathic
Fluid
Flo Flop between layers is rare
Double layer forms the basic structure
Example: Animal Cell Membrane
Mosaic of Proteins
Integral
Float like “icebergs” in a lipid “ocean”
Arrangement allows for flexibility
Cholesterol
Acts as a fluidity buffer
Hot temperatures
Stabilizes/ slows movement
Cold temperatures
Prevent tight packing
Plants use steroid lipids instead
Membrane Proteins
Definition: Functional proteins attached to and apart to the bilayer
Types:
Peripheral
Loosely bound to the surface
Integral
Embedded in hydrophobic core
Transmembrane
Spans the entire bilayer
Functons
Transport
Channel Proteins
Allows passing of ions/ water
Carrier Proteins
shape change to transport molecules
Example: Aquaporins for water
Enzymatic Activity
Catalyze reactions at membrane
Signal Transduction
Receptors for hormones and signals
Example: Insulin Receptor
Cell to Cell Recognition
Glycoproteins and glycolipids act as ID tags
Example: Blood type antigens
Intercellular Joining
Tight junctions, desmosomes, gap junctions
Attachment to Cytoskeleton and ECM
Provides structure and stability
Example: Integrins
Membrane Sidedness/ Vesicle Transport
Inner and outer faces are distinct
Orientation of proteins and lipids are preserved
ER
Golgi
Vesicle
Plasma Membrane
Membrane Composition determined during vesicle formation
Example: Inserting of insulin receptor
Selective Permeability
Definition: Membrane lets specific molecules or pass while restricting others
Free crosses
Nonpolar Molecules
O₂
CO₂
hydrocarbons
Small uncharged molecules
Requires Transport
Polar Molecules
Glucose
Water
Ions
Na⁺
K⁺
Cl⁻
Hydrophobic interior blocks polar/charged molecules
Example: CO₂ diffusion vs glucose needing transporters
Passive Transport
Definition: Movement down concentration gradient, no ATP required.
Simple Diffusion
Direct passage through bilayer
Example: O₂ entering cells
Facilitated Diffusion
Uses channel or carrier proteins
Specific and saturable
Example: Glucose proteins
Osmosis
Water movement across membrane
Through aquaporins or through bilayer
Example: Water balance in red blood cells
Tonicity
Definition: Ability of solution or cause water movement in or out of a cell
Animal Cells
Isotonic
Stable volume
Hypotonic
Swell, lysis
Hypertonic
shrink, crenation
Plant Cells
Isotonic
Flaccid
Hypotonic
Turgid
Hypertonic
Plasmolysis
Examples:
Red blood cells in pure water burst
Plant cells in salt water shrink away from cell wall
Active Transport
Definition: Moves substances against concentration gradient, needs ATP
Features
Uses carrier proteins
Keeps gradients across membrane
Sodium Potassium Pump
3 Na⁺ out, 2 K⁺ in
Maintains a negative membrane potential
Example: Nerve impulse transmissoin
Membrane Potential
Definition: Voltage difference across membrane because of ion gradients
The inside is usually negative compared to outside
Created by active transport
Example: Na⁺/K⁺ pump, proton pump
Initiates passive transport of ions
Example: Proton pumps in plant cells
Co-Transport
Definition: Active transport of one molecule results in the passive transport of another
Proton gradient drives uptake of sugars
Example: H⁺/Sucrose co-transporter in plant cells
Coupling mechanisms makes it more effiicent
Bulk Transport
Definition: Movement of large molecules through vesicles
Exocytosis
Vesicles fuse with plasma membrane
Release molecules to outside
Example: Insulin secretion
Endocytosis
Phagocytosis
Cell eating
Example: WBC engulfing bacteria
Pinocytosis
Cell drinking
Receptor mediated endocytosis
specific molecules uptake