🦠 Prokaryotic vs. Eukaryotic Cells

Cell Theory

1. All living things are composed of cells
2. The cell is the basic unit of life
3. All cells come from preexisting cells

Prokaryotic Cells

Characteristics:

• No nucleus - DNA in nucleoid region
• No membrane-bound organelles
• Smaller (1-10 μm)
• Examples: Bacteria, Archaea

Structures:

• Nucleoid: region containing circular DNA
• Ribosomes: protein synthesis (70S)
• Cell wall: peptidoglycan (bacteria)
• Plasma membrane: phospholipid bilayer
• Capsule: protective outer layer (some)
• Flagella: movement (some)
• Pili: attachment, DNA transfer (some)

Eukaryotic Cells

Characteristics:

• Nucleus with nuclear envelope
• Membrane-bound organelles
• Larger (10-100 μm)
• Examples: Animals, plants, fungi, protists

Structures:

• Nucleus: contains DNA
• Membrane-bound organelles:
  • Mitochondria
  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes (animals)
  • Peroxisomes
• Ribosomes: 80S (larger than prokaryotic)
• Cytoskeleton: structural support, movement

Plant vs. Animal Cells

Unique to Plants:

• Cell wall: cellulose
• Chloroplasts: photosynthesis
• Central vacuole: storage, turgor pressure
• Plasmodesmata: channels between cells

Unique to Animals:

• Centrioles: organize spindle fibers
• Lysosomes: digestion (rare in plants)

Surface Area to Volume Ratio

Importance:

• Limits cell size
• Larger cells have lower SA:V ratio
• Less efficient diffusion as cells grow
• Cells divide to maintain high SA:V

Calculation: For a cube with side length a:

• Surface area = 6a²
• Volume = a³
• Ratio = 6a²/a³ = 6/a

As a increases, ratio decreases!

Key Concepts

1. Prokaryotes lack nucleus and organelles
2. Eukaryotes have nucleus and organelles
3. Plant cells have cell wall, chloroplasts, central vacuole
4. Surface area to volume ratio limits cell size
5. All cells have plasma membrane, ribosomes, DNA