Prokaryotic vs. Eukaryotic Cells – Vocabulary Review

Structural and Functional Features

• Ribosomes as the First Point of Comparison
  • Both cell types contain ribosomes (site of protein synthesis).
  • Prokaryotes: 70\,S ribosome.
  – “S” = Svedberg unit, a sedimentation‐rate measure used after ultracentrifugation; reflects size + shape, not strict mass.
  – Practical link: many antibiotics exploit the 70\,S vs 80\,S distinction for selective toxicity (kill bacteria, spare host).
  • Eukaryotes: 80\,S ribosome.

• Nuclear Organization
  • Eukaryotes possess a membrane-bound nucleus that packages and protects DNA (chromosomes neatly arranged).
  • Prokaryotes lack a nucleus; DNA resides in a loosely organized nucleoid region.
  • Microscopy cue: spotting a visible nucleus ➜ immediately classifies the specimen as eukaryotic.

• Energy Centers
  • Eukaryotic cells have mitochondria (“powerhouse”): site of aerobic respiration and ATP production.
  • Prokaryotes generate ATP by other strategies (to be covered later) and do not contain mitochondria.

• Membrane-Bound Organelles (MBOs)
  • Exclusive to eukaryotes:
  – Endoplasmic Reticulum (ER)
  • Rough ER (ribosome-studded) = protein synthesis & initial modification.
  • Smooth ER = lipid synthesis & detoxification.
  – Golgi Apparatus = post-translational modification, packaging, targeting for secretion or intracellular use.
  • Prokaryotes completely lack MBOs.

Shared Cellular Components

• DNA
  • Universal: same four nucleotides (A, T, G, C) encode genetic info across all life.

• Flagella (Motility)
  • Present in some representatives of both groups.
  – Prokaryotic flagella differ structurally, but functionally propel the cell.
  – Eukaryotic examples: human sperm; various motile protozoa.

• Cell Walls
  • Both groups contain species with walls, but chemical makeup diverges:
  – Prokaryotes: typically peptidoglycan or analogs.
  – Eukaryotes (if wall present): diverse polymers—e.g.
  • Algae: cellulose, silica, or calcium carbonate.
  • Fungi: chitin, glucans, mannoproteins.

• Cytoplasm
  • Gel-like matrix (mainly water + salts, sugars, electrolytes).
  • Suspends all internal components.

• Plasma (Cell) Membrane
  • Universally a phospholipid bilayer: two layers of amphipathic phospholipids.
  • Embedded transmembrane proteins & channels enable:
  – Signal transduction (outside ➜ inside).
  – Regulated transport of ions & molecules.

Specialized Prokaryotic Adaptations

• Pili & Fimbriae
  • Surface appendages that mediate attachment to host cells/tissues.
  • Crucial in colonization and sometimes genetic exchange (conjugation pili).

• Endospores
  • Dormant, highly resistant structures produced by some bacteria under stress (heat, desiccation, nutrient deprivation).
  • Process:

  1. Sporulation – encapsulates DNA in a tough coat.

  2. Environmental conditions improve ➜ Germination back to vegetative, metabolically active state.

• Capsule / Glycocalyx
  • Secreted polysaccharide layer outside cell wall.
  • If thick & organized ➜ “capsule”; if loose ➜ “slime layer.”
  • Functions:
  – Attachment to host surfaces (biofilm initiation).
  – Evasion of immune phagocytosis (blocks engulfment).

Additional Functional Insights & Connections

• Selective Toxicity
  • Medical importance: antibiotics that target 70\,S ribosomes spare host (human) 80\,S ribosomes → reduced side effects.

• “Powerhouse” Reminder
  • Classic A&P concept: mitochondrial ATP production underscores high energy demand in eukaryotic processes.

• Microscopy & Diagnostics
  • Presence/absence of nucleus and organelles aids rapid cell classification in lab settings.
  • Acid-fast & Gram staining further interrogate prokaryotic wall composition (covered in later units).

• Environmental & Evolutionary Considerations
  • Endospore-forming bacteria pose sterilization challenges (healthcare, food industry).
  • Flagellar diversity hints at evolutionary solutions to motility across domains of life.