Overview

Cells are the basic units of life, and organelles are specialized structures within cells that perform essential functions. Biology distinguishes between prokaryotic cells (simple, no nucleus) and eukaryotic cells (complex, with organelles). Understanding cell structure and function is fundamental to all areas of biology.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes: Bacteria and Archaea. No nucleus; DNA is free-floating. Small, simple structure.
• Eukaryotes: Animals, plants, fungi, and protists. DNA housed in nucleus. Contain membrane-bound organelles.

Key Organelles and Their Functions

• Nucleus: Contains DNA and coordinates gene expression.
• Ribosomes: Assemble proteins (can be free-floating or on rough ER).
• Endoplasmic Reticulum (ER):
  • Rough ER: Studded with ribosomes; modifies proteins.
  • Smooth ER: Synthesizes lipids and detoxifies chemicals.
• Golgi Apparatus: Sorts and packages proteins and lipids.
• Mitochondria: Powerhouse of the cell; site of cellular respiration.
• Chloroplasts: Conduct photosynthesis (found in plants and algae).
• Lysosomes: Contain enzymes that digest cellular waste.
• Vacuoles: Storage; large central vacuole in plant cells maintains turgor pressure.
• Cell Membrane: Regulates what enters and exits the cell; composed of a phospholipid bilayer.
• Cytoskeleton: Maintains cell shape and enables movement.

Cell Membrane Properties

• Fluid Mosaic Model: Membrane is dynamic with proteins embedded in a lipid bilayer.
• Selective Permeability: Only certain molecules pass freely; others require transport proteins.
• Transport Mechanisms: Diffusion, osmosis, active transport, facilitated diffusion.

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