E c o

• Energy-Converting Organelles


  Mitochondria and chloroplasts change energy from one form to another
• Mitochondria


  • Sites of cellular respiration, a metabolic process that uses oxygen to generate ATP
• Chloroplasts


  • Found in plants and algae, sites of photosynthesis

  
• Mitochondria and chloroplasts


  • Enveloped by a double membrane
  • Contain free ribosomes and circular DNA molecules
  • Grow and reproduce somewhat independently in cells
• The Endosymbiont theory


  1. An early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host

  2. The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion

  3. At least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts
• Mitochondrion


  • Smooth outer membrane
  • Inner membrane folded into cristae
  • Two compartments: intermembrane space and mitochondrial matrix
  • Some metabolic steps of cellular respiration catalyzed in the mitochondrial matrix
  • Cristae present a large surface area for enzymes that synthesize ATP
• Intermembrane space


  Narrow region between the inner and outer membranes
• Mitochondrial matrix


  Contains mitochondrial DNA, ribosomes, and many enzymes that catalyze some of the reactions of cellular respiration
• Chloroplast


  • Contains the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis
  • Found in leaves and other green organs of plants and in algae
  • One of a group of plant organelles called plastids

  
• Intermembrane space


  Thin space between the outer and inner membrane
• Stroma


  Thick fluid inside the inner membrane that contains the chloroplast DNA, ribosomes, and many enzymes
• Thylakoids


  Network of interconnected sacs inside the chloroplast
• Granum


  Stacks of thylakoids where green chlorophyll molecules trap solar energy