LS14+160+Membrane+S2025
Page 1: Lipids
Mostly made of carbon and hydrogen
Hydrophobic Fatty Acid
Carboxyl group: Hydrophilic tail, hydrophobic
Can be saturated or unsaturated
Phospholipid
Always two tails
Main ingredient of membranes
Triacylglycerol
Composed of phosphate
Hydrophilic part
Steroid
Example: Cholesterol
Function: Energy storage molecules
Page 2: Composition of Bacterial Cell
Importance of macromolecules
Bacterial cell composition: 30% chemicals, 4% ions/small molecules, 2% phospholipids, 1% DNA, 6% RNA, 15% proteins, 70% H₂O, 2% polysaccharides
Page 3: Comparison of Macromolecules
Comparison of E. coli dry mass vs Human cell dry mass:
Inorganic
Other organic
Polysaccharides
Lipids
DNA
RNA
Proteins
Page 4: Membranes and Transport
Generalized animal cell components:
Golgi apparatus
Nuclear envelope
Nucleus
Rough/Smooth endoplasmic reticulum
Peroxisome
Lysosome
Mitochondrion
Plasma membrane
Page 5: Plasma Membrane Functions
Forms boundary with selective permeability
Allows entry of needed compounds, excludes damaging compounds
Enables distinct internal environment compared to external
Other cellular membranes facilitate compartmentalization for efficiency
Page 6: Lipid Bilayer Structure
Membranes made of lipid bilayers:
Hydrophilic heads face water
Hydrophobic tails are shielded from water
Page 7: Concentration Gradient
Definition: Difference in solute concentrations across a barrier
Membranes lead to formation and maintenance of concentration gradients
Key questions:
Why do molecules cross membranes?
How do molecules cross membranes?
Page 8: Molecular Movement
Molecules and ions move randomly (diffusion)
Net movement from high to low concentration regions
Spontaneous process (requires no energy)
Page 9: Artificial Membranes Experiments
Artificial membranes can be used to study phospholipid bilayer permeability
Investigate whether molecules can cross the bilayer
Page 10: Movement Across Lipid Bilayer
Molecules/ions separate by lipid bilayer
Spontaneous diffusion occurs from high to low concentration
Page 11: Equilibrium in Molecule Movement
Achieved when molecules/ions are uniformly distributed
No net movement despite continued random movement
Page 12: Water Movement
Water can move across lipid bilayers
Net movement from high water concentration (low solute) to low water concentration (high solute)
Page 13: Definition of Osmosis
Special case of diffusion for water across selectively permeable membranes
Page 14: Passive Transport
Movement of O2, CO2, and some water via passive diffusion
Cross membranes along concentration gradients
Page 15: Factors Affecting Membrane Permeability
Structure of fatty acid tails affects permeability (double bonds = higher permeability)
Cholesterol content (increases = lower permeability) and temperature (higher = higher permeability)
Page 16: Factors Influencing Speed of Movement
Quickness of molecules' movement influenced by:
Temperature
Structure of hydrocarbon tails
Cholesterol amount in bilayer
Page 17: Osmosis Example with Blood Cells
Comparison of blood cells in hypertonic, isotonic, and hypotonic solutions.
Page 18: Solution Comparisons
Key terms: Hypertonic (excessive), Isotonic (equal), Hypotonic (under)
Comparing solutions with varying solute amounts.
Page 19: Water Flow in Solutions
Net water flow can lead to swelling or shrinking of vesicles depending on outside solutions.
Page 20: IV Therapy
Blood cells in plasma; isotonic solutions in IV therapy.
Page 21: Hypotonic Solutions
Effects of hypotonic solutions on cells (e.g., swelling).
Page 22: Cell Walls Function
Cell walls prevent bursting and define shape; contractile vacuoles pump water out of freshwater protozoa.
Page 23: Membrane Models
Sandwich model vs. Fluid-mosaic model described in terms of cell architecture.
Membrane proteins in relation to phospholipid bilayer.
Page 24: Freeze-Fracture Preparations
Technique to view membrane proteins and structures.
Page 25: Protein Types
Integral (transmembrane) proteins span the membrane; peripheral proteins attach only to one side.
Page 26: Amphipathic Proteins
Properties of amphipathic proteins that aid in membrane integration.
Page 27: Molecule Permeability
Different molecules have varying abilities to cross the phospholipid bilayer.
Page 28: Integral Proteins and Transport
Integral proteins facilitate transport of molecules across membranes.
Page 29: Aquaporin Example
Example of facilitated diffusion: aquaporin as a selective water channel.
Page 30: Membrane Transport Mechanisms
Two mechanisms: Diffusion and Facilitated diffusion.
Page 31: Overall Learning Objectives
Importance of membranes, osmotic processes, and predicting solute/water flow.
Distinction between osmosis, diffusion, and facilitated diffusion.
Understanding phospholipid bilayer dynamics and transport rates.
Identify membrane proteins and their roles.
Page 32: Vocabulary
Key terms:
Plasma membrane
Organelles
Compartmentalization
Concentration gradient
Diffusion
Facilitated diffusion
Integral and peripheral proteins
Aquaporin
Osmosis
Hypotonic, Isotonic, Hypertonic
Page 33: Homework Assignment
Complete Mastering Biology assignment.
Review Chapter 6.4.
Page 34: Detailed Written Homework
Analyze and explain Fig. 6.15.
Propose an experiment with liposomes regarding membrane permeability.