Chapter 1: Cells: The Fundamental Units of Life

UNITY AND DIVERSITY OF CELLS

  • Living cells vary enormously in appearance and function; all share a similar basic chemistry.
  • Living cells are self-replicating collections of catalysts.
  • All living cells have evolved from the same ancestral cell.
  • Genes provide instructions for the form, function, and behavior of cells and organisms.

CENTRAL DOGMA AND BASIC CHEMISTRY

  • Core processes: DNA replication, transcription, translation.
  • Flow: DNA -> RNA -> Protein; nucleotides and amino acids determine structure and function.
  • DNA synthesis, RNA synthesis, protein synthesis.

CELLS UNDER THE MICROSCOPE

  • Light microscopy reveals some cell components; electron microscopy reveals fine structure.
  • Light microscopy resolution ~ 0.2 μm; magnification up to ~1000×; three requirements: light focused onto specimen by condenser; light passes through fixed specimen; appropriate lenses.
  • Fixed samples: tissues fixed and sectioned, stained to reveal components.
  • Living cells: bright-field, phase-contrast, interference-contrast; differences in refractive index.
  • Fluorescence microscopy: fluorescent dyes; antibodies; GFP; detection with filters; can see objects smaller than 0.2 μm.
  • Confocal fluorescence: scanning with a laser to produce optical sections; 3D image.
  • Super-resolution fluorescence microscopy: methods with 20 nm resolution; 3D/live-cell imaging.
  • TEM: uses electrons; resolution up to ~1 nm; thin sections; heavy metal stains; vacuum.
  • SEM: 3D images with depth; resolution ~3-20 nm; coated with thin heavy metal.

THE PROKARYOTIC CELL

  • Prokaryotes are the most diverse and numerous cells on Earth.
  • Two domains: Bacteria and Archaea.
  • Shapes: spherical (cocci), rod-shaped (bacilli), spiral (spirilla).
  • Cytoplasm; plasma membrane; outer membrane (some); cell wall.

THE EUKARYOTIC CELL

  • The nucleus is the information store.
  • Mitochondria generate usable energy from food molecules; double membranes.
  • Chloroplasts capture energy from sunlight.
  • Internal membranes create intracellular compartments with different functions.
  • The cytosol is a concentrated aqueous gel of large and small molecules.
  • The cytoskeleton is responsible for directed cell movements.
  • Eukaryotic cells may have originated as predators (endosymbiotic origin).

MODEL ORGANISMS

  • Model organisms and their genomes
  • E. coli (bacterium): genome ≈ 4.6 million bp; about 4,300 genes.
  • Saccharomyces cerevisiae (yeast): ≈ 12.5 million bp; ~6,600 genes.
  • Caenorhabditis elegans (roundworm): ≈ 100 million bp; ~22,000 genes.
  • Drosophila melanogaster (fruit fly): ≈ 180 million bp; ~14,000 genes.
  • Arabidopsis thaliana (plant): ≈ 103 million bp; ~28,000 genes.
  • Homo sapiens (human): ≈ 3,200 million bp; ~19,000 genes.
  • Mus musculus (mouse): ≈ 2,800 million bp; ~22,000 genes.
  • Note: Genome size includes highly repetitive noncoding DNA; genomes reveal life’s common heritage.
  • Genomes contain more than just genes.