BIOL1610 W25 Lipids & membranes

Molecular Interactions with Water

  • Question posed: Do the given molecules interact with water?

  • Molecules represented: A combination of hydrocarbon and functional groups, such as H3C and CH3, suggesting variances in hydrophobic and hydrophilic properties.

Types of Lipids

Three Main Types

  • Fats

  • Phospholipids

  • Steroids

  • Described as largely non-polar, which influences their interactions with water.

Fats (Triacylglycerols)

Structure and Composition

  • Composed of glycerol and three fatty acids.

  • Example given: Palmitic acid as a fatty acid component.

Synthesis

  • Formation involves dehydration reactions, leading to the formation of ester linkages.

Functions

  • Energy storage

  • Insulation and protection

Steroids

Characteristics

  • Amphipathic: Containing both polar/hydrophilic and nonpolar/hydrophobic elements.

  • Formula details: Include a mix of hydrophilic (HO) and hydrophobic (C-CH3) regions.

Functions

  • Hormonal functions

  • Components of cell membranes.

Phospholipids

Structure

  • Composed of a hydrophilic head (containing phosphate and choline) and two hydrophobic tails (fatty acids).

  • Self-organizing behavior when placed in water leading to bilayer formation.

Arrangement in Water

Micelles vs. Bilayers

  • Lipid Micelles

    • Formed when phospholipids aggregate.

  • Lipid Bilayers

    • Result from hydrophilic heads interacting with water while hydrophobic tails interact among themselves.

Phospholipid Bilayer

Fluidity Properties

  • Fluid nature allows lateral motion and rare flipping of phospholipids.

  • Fluidity increases with temperature.

Fatty Acids Variation

Impact on Membrane Structure

  • Differences in:

    • Length of carbon chains

    • Number and placement of C-C double bonds

  • Saturated fatty acids: increase stacking interactions, reducing fluidity.

  • Unsaturated fatty acids: introduce kinks, increasing fluidity.

Membrane Composition Effects

Saturated vs. Unsaturated Fatty Acids

  • Increased degree of unsaturation enhances membrane permeability.

  • Comparisons include effects on permeability found in substances like safflower oil and butter.

Role of Cholesterol in Fluidity

  • At higher temperatures, cholesterol fills spaces between phospholipids, limiting movement.

  • At lower temperatures, it prevents fatty acid chain stacking, aiding fluidity.

Membrane Functionality

Selective Permeability

  • Mechanism facilitates controlled entry and exit of materials.

  • Substance classes impacting permeability include presence of saturated vs. unsaturated fatty acids and cholesterol concentration.

Molecular Movement

Concepts of Diffusion and Osmosis

  • Concentration Gradient: Difference in concentration of a molecule across a distance.

  • Net Directional Movement: Overall population trend despite individual randomness.

  • Diffusion: Spontaneous net movement from high to low concentration until equilibrium.

  • Osmosis: Specific diffusion of water across a permeable membrane.

Tonicity and Osmosis

Definitions

  • Hyper-osmotic: Higher solute concentration outside cell.

  • Hypo-osmotic: Lower solute concentration outside cell.

  • Iso-osmotic: Equal solute concentration.

Effects on Cells

  • Hypotonic solutions cause water influx, swelling cells.

Membrane Proteins

Types and Functions

  • Categories include integral and peripheral proteins involved in transport across the membrane.

Transport Mechanisms

Types of Transport Proteins

  1. Channels: Allow passive movement of molecules along gradients.

  2. Carriers/Transporters: Bind molecules and change shape to facilitate crossing.

  3. Pumps: Active transport mechanisms requiring energy.

Channels vs. Carriers

  • Channel: Allows passage through size and charge selectivity.

  • Carrier: Utilizes conformational changes to transport specific molecules.

Active Transport and Sodium-Potassium Pump

Functionality

  • Na+/K+-ATPase mechanism:

    • 3 Na+ ions out, 2 K+ ions in.

    • Uses ATP to maintain ion gradients across the membrane.

Overview of Active Transport Mechanism

  • Generates concentration gradients, thereby creating potential energy used in cell processes.

Endocytosis

Import Mechanisms

  • Processes include phagocytosis, pinocytosis, and receptor-mediated endocytosis, allowing cells to import various materials.