Endosymbiotic Theory & Intercellular Junctions

Friday, November 18th, 2023

Objectives:

• Explain the endosymbiotic theory
• Name and describe the types of intercellular junctions

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Concept 4.5

Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP

Chloroplasts, found in plants and algae, are the sites of photosynthesis

peroxisomes are oxidative organelles

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The Evolutionary origins of Mitochondria and Chloroplasts

• Mitochondria and chloroplasts display similarities with bacteria
• Enveloped by a double membrane
• Contain ribosomes and multiple circular DNA molecules
• Grow and reproduce somewhat independently in cells

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The endosymbiont theory

• An early ancestor of eukaryotic engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host
• The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion
• At least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts

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• Mitochondria are in nearly all eukaryotic cells
• They have a smooth outer membrane and an inner membrane folded into cristae
• The inner membrane creates two compartments: intermembrane space and mitochondrial matrix
• Come metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix
• Cristae present a large surface area for enzymes that synthesize ATP

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Chloroplast: Capture of Light Energy

• Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis
• Chloroplasts are found in leaves and other green organs of plants and in algae
• Chloroplast structure includes
  • Thylakoids, membranous sacs, stacked to form a granum
  • Stroma, the internal fluid
• The chloroplast Is one of a group of plant organelles called plastids

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