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General Biology I: Mitochondria and Chloroplasts

General Biology I
Mitochondria and Chloroplasts
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Introduction
  6. 1. Reference Information
    1. Presenting Data
    2. Using credible sources
    3. Citing your sources
    4. Writing for Science
  7. The Process of Science
    1. The Nature of Science
    2. Scientific Inquiry
    3. Hypothesis Testing
    4. Types of Data
    5. Basic and Applied Science
    6. Reporting Scientific Work
  8. Themes and Concepts of Biology
    1. Properties of Life
    2. Levels of Organization of Living Things
    3. The Diversity of Life
    4. Phylogenetic Trees
  9. Cell Structure and Function
    1. How Cells Are Studied
    2. Comparing Prokaryotic and Eukaryotic Cells
    3. The Plasma Membrane and The Cytoplasm
    4. Ribosomes
    5. The Cytoskeleton
    6. Flagella and Cilia
    7. The Endomembrane System
    8. The Nucleus
    9. The Endoplasmic Reticulum
    10. The Golgi Apparatus
    11. Vesicles and Vacuoles, Lysosomes, and Peroxisomes
    12. Mitochondria and Chloroplasts
    13. The Cell Wall
    14. Extracellular matrix and intercellular junctions
    15. Animal vs Plant cells
    16. The Production of a Protein
    17. Chapter Quiz
    18. Summary Table of Prokaryotic and Eukaryotic Cells and Functions
  10. Membranes and movement of molecules
    1. The Plasma Membrane
    2. Transport Across Membranes
    3. Passive Transport: Diffusion
    4. Passive Transport: Osmosis
    5. Active Transport
  11. Enzyme-catalyzed reactions
    1. Metabolic Pathways
    2. Energy
    3. Enzymes
    4. Changes in Enzyme Activity
    5. Feedback Inhibition in Metabolic Pathways
  12. How cells obtain energy
    1. Energy in Living Systems
    2. From Mouth to Molecule: Digestion
    3. Metabolism
    4. An overview of Cellular Respiration
    5. Aerobic Respiration: Glycolysis
    6. Aerobic Respiration: The Citric Acid Cycle
    7. Aerobic Respiration: Oxidative Phosphorylation
    8. Fermentation: an anaerobic process
    9. Metabolism of molecules other than glucose
    10. Anaerobic Cellular Respiration
  13. Photosynthesis
    1. Putting Photosynthesis into Context
    2. Light and Pigments
    3. Light Dependent Reactions
    4. The Calvin Cycle
    5. Photosynthesis in Prokaryotes

26

Mitochondria and Chloroplasts

Mitochondria

Mitochondria (singular = mitochondrion) are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule. The formation of ATP from the breakdown of glucose is known as cellular respiration. Mitochondria are oval-shaped, double-membrane organelles (Figure 1) that have their own ribosomes and DNA. Each membrane is a phospholipid bilayer embedded with proteins. The inner layer has folds called cristae, which increase the surface area of the inner membrane. The area surrounded by the folds is called the mitochondrial matrix. The cristae and the matrix have different roles in cellular respiration.

In keeping with our theme of form following function, it is important to point out that muscle cells have a very high concentration of mitochondria because muscle cells need a lot of energy to contract.

figure_03_14
Figure 1 This transmission electron micrograph shows a mitochondrion as viewed with an electron microscope. Notice the inner and outer membranes, the cristae, and the mitochondrial matrix. (credit: modification of work by Matthew Britton; scale-bar data from Matt Russell)

Like mitochondria, chloroplasts also have their own DNA and ribosomes. Chloroplasts function in photosynthesis and can be found in eukaryotic cells such as plants and algae. Carbon dioxide (CO2), water, and light energy are used to make glucose and oxygen in photosynthesis. This is the major difference between plants and animals: Plants (autotrophs) are able to make their own food, like glucose, whereas animals (heterotrophs) must rely on other organisms for their organic compounds or food source.

Like mitochondria, chloroplasts have outer and inner membranes, but within the space enclosed by a chloroplast’s inner membrane is a set of interconnected and stacked, fluid-filled membrane sacs called thylakoids (Figure 2). Each stack of thylakoids is called a granum (plural = grana). The fluid enclosed by the inner membrane and surrounding the grana is called the stroma.

figure_03_15
Figure 2 This simplified diagram of a chloroplast shows the outer membrane, inner membrane, thylakoids, grana, and stroma.

 The chloroplasts contain a green pigment called chlorophyll, which captures the energy of sunlight for photosynthesis. Like plant cells, photosynthetic protists also have chloroplasts. Some bacteria also perform photosynthesis, but they do not have chloroplasts. Their photosynthetic pigments are located in the thylakoid membrane within the cell itself.

Theory of Endosymbiosis

We have mentioned that both mitochondria and chloroplasts contain DNA and ribosomes. Have you wondered why? Strong evidence points to endosymbiosis as the explanation.

Symbiosis is a relationship in which organisms from two separate species live in close association and typically exhibit specific adaptations to each other. Endosymbiosis (endo-= within) is a relationship in which one organism lives inside the other. Endosymbiotic relationships abound in nature. Microbes that produce vitamin K live inside the human gut. This relationship is beneficial for us because we are unable to synthesize vitamin K. It is also beneficial for the microbes because they are protected from other organisms and are provided a stable habitat and abundant food by living within the large intestine.

Scientists have long noticed that bacteria, mitochondria, and chloroplasts are similar in size. We also know that mitochondria and chloroplasts have DNA and ribosomes, just as bacteria do. Scientists believe that host cells and bacteria formed a mutually beneficial endosymbiotic relationship when the host cells ingested aerobic bacteria and cyanobacteria but did not destroy them. Through evolution, these ingested bacteria became more specialized in their functions, with the aerobic bacteria becoming mitochondria and the photosynthetic bacteria becoming chloroplasts.

References

Unless otherwise noted, images on this page are licensed under CC-BY 4.0 by OpenStax.

Text adapted from: OpenStax, Concepts of Biology. OpenStax CNX. May 18, 2016 http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.10

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Copyright © 2016 by Lisa Bartee and Christine Anderson. Mt Hood Community College Biology 101 by Lisa Bartee and Christine Anderson is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.
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