Cell Biology Lecture 2: Cellular Structure and DNA

Cell Ultrastructure and Genetic Materials

• The three domains of life: Bacteria, Archaea, and Eukarya
• Criteria for distinguishing between the three domains:
  • Small subunit rRNA: Bacteria (6 nucleotides), Archaea (7 nucleotides), Eukarya (7 nucleotides)
  • Distinct feature: Bacteria (between positions 500 and 545), Archaea (between positions 585 and 655), Eukarya (between positions 180 and 197 or 405 and 498)
  • Cell type: Bacteria and Archaea (prokaryotic), Eukarya (eukaryotic)
  • Cell wall: Bacteria (peptidoglycan), Archaea (variable; no murein), Eukarya (variable)
  • Membrane lipids: Bacteria (diacyl-D-glycerol diester), Archaea (isoprenoid L-glycerol diether or L-glycerol tetraether), Eukarya (D-glycerol unbranched diester)

Prokaryotic Cell Ultrastructure

• Cell membrane:
  • Composed of phospholipid bilayer
  • Mesosomes: folded regions of the cell membrane
  • Magnetosome: found in magnetotactic bacteria, allows them to sense and align themselves along a magnetic field
• Bacterial cell wall:
  • Composed of peptidoglycan (also called murein)
• Capsule: protective layer that surrounds the cell wall
• Pili (Fimbriae): involved in conjugation and longer than fimbriae
• Flagellum: for movement or motility
• Nucleoid: where genetic material resides, not a true nucleus
• Plasmids: small, circular DNA molecules that can replicate independently of the chromosomal DNA
• Ribosomes: responsible for protein synthesis
• Cytosol: liquid found inside cells
• Storage granules: store nutrients or other substances
• Cytoskeleton: provides support, gives shape, and is involved in movement

Gram Staining

• Gram (+): thick peptidoglycan, teichoic acids, and lipoteichoic acids
• Gram (-): thin peptidoglycan, lipopolysaccharides, lipoproteins, and phospholipids
• Periplasmic space: present in Gram (-) bacteria, absent in Gram (+) bacteria
• Basal rings: one pair in Gram (+) bacteria, two pairs in Gram (-) bacteria

Eukaryotic Cell Ultrastructure

• Lysosomes: involved in digestion and recycling
• Peroxisomes: contain peroxidase and catalase enzymes
• Endoplasmic reticulum: involved in protein synthesis, sugar synthesis, and detoxification
• Golgi apparatus: packaging center
• Nucleus: control center of the cell, regulates the activities of the cell
• Nuclear pores: where mRNA exits before being translated by ribosomes
• Mitochondria: powerhouse of the cell, responsible for energy production
• Chloroplasts: site of photosynthesis, formation of starch and lipid synthesis