AA

BIOL 215 Lecture 5

Eukaryotic Subcellular Structures (Continued)

Vacuoles

  • Vacuoles: storage compartments formed by a lipid bilayer
  • Plant cells have one large vacuole while animal cells have multiple small vacuoles
  • Different functions of vacuoles
    • The central vacuole in plants
    • stores organic molecules and water
    • is responsible for creating turgor pressure to support the plant
    • maintains fluid balance
    • Phagosomes: vacuoles storing food that the cell takes in
    • Contractile vacuoles: vacuoles that expand and contract to expel excess water in the cell
    • They are responsible for osmoregulation

Mitochondria

  • Mitochondria are found in most eukaryotes
    • Photosynthetic organisms also have mitochondria!!
  • Mitochondria are the site of cellular respiration

Chloroplasts

  • Chloroplasts are the site of photosynthesis
  • They are only found in photosynthetic eukaryotes

Cellular Evolution

Origin of the Endomembrane System

  • The endomembrane system originated from the infolding of the plasma membrane to increase available surface area.

Endosymbiotic Theory

  • Symbiosis: a close, long-term interaction between two species
  • The modern mitochondria and chloroplasts used to be free-living prokaryotes that were engulfed by larger prokaryotes
    • Mitochondria are related to proteobacteria
    • Chloroplasts are related to cyanobacteria
  • The mitochondria or chloroplast and the larger prokaryotic cell developed a symbiotic relationship
    • They became so dependent on each other that they became one cell

Evidence for the Endosymbiotic Theory

  • Mitochondria and chloroplasts are similar in size to prokaryotes
  • Mitochondria and chloroplasts replicate by binary fission
  • They have a double membrane
    • The inner membrane is similar to a prokaryotic plasma membrane
    • Outer membrane maybe originated from phagocytosis when the mitochondria or chloroplast was engulfed by a large prokaryote
  • Mitochondria and chloroplasts have 70S ribosomes
  • Their genome is circular
  • Genome sequence similarity
    • The mitochondrial genome is similar to proteobacterial genomes
    • The chloroplast genome is similar to cyanobacterial genomes
  • Reduced organelle genomes
    • The mitochondria or chloroplast and host transferred DNA amongst each other by horizontal gene transfer
    • Horizontal gene transfer: non-sexual movement of genetic information between genomes of the same generation
    • Lots of genes needed by the mitochondria or chloroplast are now in the nucleus
    • These genes are similar to genomes of proteobacteria or cyanobacteria