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

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