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

This quiz covers the ultrastructure of cells, including genetic material and types of DNA. It also touches on the three domains of life and the presence of operons and introns.