Functional Anatomy of Prokaryotic and Eukaryotic Cells: Study Notes

Functional Anatomy of Prokaryotic and Eukaryotic Cells

Prokaryotic Cells

Prokaryotic cells are simple, unicellular organisms that lack a nucleus and membrane-bound organelles. They are primarily represented by bacteria and archaea.

• Genetic Material: Usually contain one circular chromosome.

• Nuclear Region: DNA is not enclosed in a membrane-bound nucleus.

• Organelles: Lack membrane-bound organelles.

• Cell Wall: Bacterial cell walls contain peptidoglycan.

• Reproduction: Reproduce by binary fission.

• Examples: Escherichia coli, Staphylococcus aureus

Eukaryotic Cells

Eukaryotic cells are more complex, with DNA enclosed within a nuclear membrane and various membrane-bound organelles. They include plants, animals, fungi, and protists.

• Genetic Material: DNA enclosed within a nuclear membrane.

• Organelles: Contain membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).

• Size: Larger and more complex than prokaryotes.

• Division: Divide by mitosis or meiosis.

• Examples: Plants, animals, fungi, protists.

Bacterial Shapes and Arrangements

Bacterial Shapes

• Bacillus: Rod-shaped.

• Coccus: Spherical-shaped.

• Spiral Forms:

  • Vibrio: Comma-shaped.

  • Spirillum: Rigid spiral.

  • Spirochete: Flexible spiral.

Bacterial Arrangements

• Pairs: Diplococci, diplobacilli.

• Chains: Streptococci, streptobacilli.

• Clusters: Staphylococci.

• Groups of Four: Tetrads.

Cell Structures and Their Functions

Glycocalyx

The glycocalyx is a gelatinous, sticky substance found outside the cell wall of many bacteria.

• Composition: Polysaccharides and/or polypeptides.

• Types:

  • Capsule: Firmly attached; helps prevent phagocytosis.

  • Slime Layer: Loose and unorganized; helps cells attach to surfaces.

• Functions:

  • Increases virulence.

  • Helps form biofilms.

  • Protects cells from drying out.

Flagella

Flagella are long, whip-like structures that provide motility to bacteria.

• Structure: Made of the protein flagellin.

• Arrangement Types:

  1. Monotrichous (single flagellum at one end)

  2. Lophotrichous (tuft of flagella at one or both ends)

  3. Amphitrichous (single flagellum at both ends)

  4. Peritrichous (flagella all over the cell)

• Types of Movement:

  • Run: Movement in one direction.

  • Tumble: Random direction changes.

• Chemotaxis: Movement toward or away from stimuli.

Axial Filaments

• Also called endoflagella.

• Found in spirochete bacteria.

• Cause corkscrew-like movement.

Fimbriae & Pili

• Fimbriae: Help bacteria attach to surfaces; important in biofilm formation.

• Pili:

  • DNA transfer during conjugation.

  • Twitching motility.

Cell Wall

The cell wall provides structural support and shape to the cell and is a target for many antibiotics.

• Functions:

  • Prevents osmotic lysis.

  • Protects the plasma membrane.

  • Helps determine cell shape.

  • Site of action for some antibiotics.

Gram-Positive Cell Walls

• Thick peptidoglycan layer.

• Contain teichoic acids (lipoteichoic acid links cell wall to plasma membrane; wall teichoic acid attached to peptidoglycan).

• Carry a negative charge.

Gram-Negative Cell Walls

• Thin peptidoglycan layer.

• Contain an outer membrane.

• Have a periplasmic space.

• Outer membrane contains:

  • Lipopolysaccharide (LPS)

  • Porins (protein channels through the membrane)

  • Phospholipids

• LPS parts:

  • Polysaccharide: Functions as an antigen.

  • Lipid A: Functions as an endotoxin.

Atypical Cell Walls

• Acid-Fast Bacteria: Contain waxy mycolic acid (e.g., Mycobacterium, Nocardia).

• Mycoplasmas: Lack cell walls; contain sterols in plasma membrane.

Plasma Membrane

• Structure: Made mainly of phospholipids and proteins.

• Function: Controls movement of materials into and out of the cell.

Membrane Transport

• Passive Processes: Move substances from high concentration to low concentration.

  • Simple Diffusion: No energy or transport proteins required.

  • Facilitated Diffusion: Requires membrane transport proteins.

• Osmosis: Movement of water across a selectively permeable membrane.

  • Isotonic Solution: Water movement is at equilibrium.

  • Hypotonic Solution: Water moves into the cell.

  • Hypertonic Solution: Water moves out of the cell.

• Active Processes: Move substances from low to high concentration; require energy (ATP) and transport proteins.

  • Active Transport: Requires energy and transport proteins.

  • Group Translocation: Requires transport proteins and energy; substance is chemically modified during transport.

Cytoplasm

• Mostly made of water.

• Contains DNA, ribosomes, and inclusions.

Nucleoid

• Contains the bacterial chromosome.

• Circular DNA, not enclosed by a nuclear membrane.

Plasmids

• Small circles of DNA.

• May carry genes for antibiotic resistance or toxin production.

Ribosomes

• Function: Site of protein synthesis.

• Prokaryotic Ribosomes: 70S

• Eukaryotic Ribosomes: 80S

Endospores

• Produced when nutrients are depleted.

• Functions: Survival mechanism; resistant to heat, chemicals, radiation, desiccation.

• Important Genera: Bacillus, Clostridium

Eukaryotic Organelles

Nucleus

• Contains the cell’s DNA.

• DNA is combined with histone proteins.

Endoplasmic Reticulum (ER)

• Rough ER: Contains attached ribosomes; function is protein synthesis and processing.

• Smooth ER: Function is lipid synthesis and detoxification.

Golgi Complex

• Modifies proteins.

• Packages materials into vesicles.

Lysosomes

• Contain digestive enzymes.

Mitochondria

• Site of ATP production.

• Contain circular DNA and 70S ribosomes.

Peroxisomes

• Function: Break down fatty acids and detoxify harmful substances.

Cytoskeleton

• Maintains cell shape.

• Helps with cell movement.

• Assists movement of organelles.

Flagella & Cilia in Eukaryotes

• Flagella: Long projections; few in number.

• Cilia: Short projections; numerous.

• Both contain microtubules arranged in a 9 + 2 pattern.

Summary Table: Key Differences Between Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Cell Wall	Peptidoglycan (bacteria)	Cellulose (plants), chitin (fungi), or absent (animals)
Ribosomes	70S	80S (cytoplasm), 70S (mitochondria/chloroplasts)
Division	Binary fission	Mitosis/meiosis
Size	1–10 μm	10–100 μm

Example: Gram Staining

Gram-positive bacteria retain the crystal violet stain due to their thick peptidoglycan layer, while Gram-negative bacteria do not and appear pink after counterstaining with safranin.

Additional info: Some details, such as specific examples and definitions, were inferred based on standard microbiology content to ensure completeness and clarity.