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:

  1. Why do molecules cross membranes?

  2. 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

1. Analyze and explain Fig. 6.15.

2. Propose an experiment with liposomes regarding membrane permeability.