Study Guide: Lipids, Membranes, and the First Cells

Chapter 7: Structure and Function of Plasma Membranes

Lipids

• Commonality: All lipids are hydrophobic.
• Reason for Hydrophobic Nature: Lipids are hydrophobic due to their long hydrocarbon chains which do not interact well with water molecules.
• Types of Lipids:
  • Fats
  • Phospholipids
  • Steroids

Biological Function of Fats

• Fats serve as energy storage molecules in biological organisms.

Composition of Fats

• Components: Made of glycerol and fatty acids.
• Hydrophobic Component: Fatty acids are hydrophobic.

Glycerol and Fatty Acids

• Glycerol: A three-carbon alcohol that forms the backbone of fat molecules.
• Fatty Acid: Long hydrocarbon chains with a carboxyl group.

Saturated vs. Unsaturated Fats

• State at Room Temperature: Butter (solid) vs. oil (liquid).
• Saturation:
  • Saturated Fats: No double bonds, more densely packed.
  • Unsaturated Fats: One or more double bonds.
• Breakdown: Saturated fats are harder to break down due to tighter packing.

Types of Unsaturated Fats

• Monounsaturated vs. Polyunsaturated: Single vs. multiple double bonds.
• Cis vs. Trans Fats:
  • Cis Fats: Naturally occurring, easier to break down.
  • Trans Fats: Artificially produced, harder to break down.

Phospholipids

• Structure: Hydrophilic head and hydrophobic tail.
• Hydrophobic Tail: Due to the presence of long hydrocarbon chains.
• Hydrophilic Head: Contains a phosphate group.
• In Water: Form structures such as micelles, liposomes, and bilayers.

Steroids

• Structure: Share a four-ring carbon structure and vary by side groups.
• Precursor Steroid: Cholesterol.
• Importance: Vital for growth and development in animals.

Cell Membrane

• Selective Permeability: Only certain molecules can pass through.
• Composition: Made of lipids and proteins.
• Phospholipid Interaction with Water: Hydrophilic heads face water.

Transport Mechanisms

• Passive vs. Active Transport:
  • Passive Transport: Does not require energy.
  • Active Transport: Requires ATP, moves substances from low to high concentration.
• Types of Transport: Simple diffusion, facilitated diffusion, cotransport, exocytosis, endocytosis.

Osmosis

• Movement of water molecules across a permeable membrane.
• Tonicity:
  • Hypertonic: Higher solute concentration outside.
  • Isotonic: Equal solute concentration.
  • Hypotonic: Lower solute concentration outside.

Diffusion

• Simple Diffusion: Movement of small, nonpolar molecules directly through lipid bilayer.
• Facilitated Diffusion: Utilizes membrane proteins.

Endocytosis

• Pinocytosis vs. Receptor-mediated: Pinocytosis is less specific.

Origin of First Cells

• First Cell Timeline: Best guess for emergence.
• Theories: Various hypotheses about origin.
• First Self-replicating Molecule: RNA is a likely candidate.

Autotrophs vs. Heterotrophs

• Autotrophs: Produce their own food.
• Heterotrophs: Consume other organisms for energy.
• First Cells: Likely heterotrophs.

Minimum Components of First Cells

• Needed a membrane and genetic material for replication.