Similarities between mitochondria and chloroplast

The many similarities between mitochondria and chloroplasts make more sense, and will be easier to remember, if considered in the context of where they came from. Our current understanding of their origin is the endosymbiotic theory, which says that they originated as prokaryotic organisms that were engulfed by eukaryotic cells and developed a symbiotic relationship with their host cells. Mitochondria were once prokaryotes that were able to use oxygen, and chloroplasts were once photosynthetic prokaryotes. A difference between them is that mitochondria are found in all eukaryotic cells, while chloroplasts are present only in some. Both mitochondria and chloroplasts have a double membrane. According to the endosymbiotic theory, the inner membrane is derived from the cell membrane of the ancestral prokaryote and the outer membrane from the cell membrane of the host cell during phagocytosis. Both mitochondria and chloroplasts reproduce in the cytoplasm by cell division. If they are removed from the cell, the cell is not able to make more. Both mitochondria and chloroplasts have their own DNA, which is ring-shaped like a bacterial plasmid, and their own apparatus for synthesizing proteins. Both mitochondria and chloroplasts are found only in eukaryotic cells and never in prokaryotic cells (mitochondria are in all eukaryotic cells, while chloroplasts are only in some, those of plants and some protists). Finally, the roles of the two organelles are almost the reverse of one anot...

In photosynthesis, light energy is collected and used to build sugars from carbon dioxide. The sugars produced in photosynthesis may be used by the plant cell, or may be consumed by animals that eat the plant, such as humans. The energy contained in these sugars is harvested through a process called cellular respiration, which happens in the mitochondria of both plant and animal cells. Chloroplasts are disc-shaped organelles found in the cytosol of a cell. They have outer and inner membranes with an intermembrane space between them. If you passed through the two layers of membrane and reached the space in the center, you’d find that it contained membrane discs known as thylakoids, arranged in interconnected stacks called grana (singular, granum). The membrane of a thylakoid disc contains light-harvesting complexes that include chlorophyll, a pigment that gives plants their green color. Thylakoid discs are hollow, and the space inside a disc is called the thylakoid space or lumen, while the fluid surrounding the thylakoids is called the stroma. Mitochondria (singular, mitochondrion) are often called the powerhouses or energy factories of the cell. Their job is to make a steady supply of adenosine triphosphate (ATP), the cell’s main energy-carrying molecule. The process of making ATP using chemical energy from fuels such as sugars is called The space between the membranes is called the intermembrane space, and the compartment enclosed by the inner membrane is called the mito...

Random segregation. Mitochondria and chloroplasts (and the genes they carry) are randomly distributed to daughter cells during mitosis and meiosis. When the cell divides, the organelles that happen to be on opposite sides of the cleavage furrow or cell plate will end up in different daughter cells 3 ^3 3 cubed . • Single-parent inheritance. Non-nuclear DNA is often inherited uniparentally, meaning that offspring get DNA only from the male or the female parent, not both 4 ^4 4 start superscript, 4, end superscript . In humans, for example, children get mitochondrial DNA from their mother (but not their father). At the turn of the 20th century, Carl Correns, a German botanist, did a series of genetic experiments using four o’clock plants ( Mirabilis jalapa). We now know that his work demonstrated how chloroplast DNA is passed on from cell to cell and from parent to offspring—though Correns himself didn't know it at the time 5 ^5 5 start superscript, 5, end superscript ! The Mirabilis plants that Correns worked with came in three types: pure green, pure white, or variegated (mottled green and white). Green and white branches could appear on variegated plants, but variegated branches did not appear on green or white plants 6 ^6 6 start superscript, 6, end superscript . Correns speculated that some factor in the cytoplasm of the egg cell must determine the color of the offspring. It was actually a different German botanist, Erwin Baur, who suggested that the chloroplasts in the...

Learning Objectives • Briefly describe what is meant by the endosymbiotic theory. • Give some evidence supporting the theory that mitochondria and chloroplasts may have arisen from prokaryotic organisms. It is thought that life arose on earth around four billion years ago. The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes. In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship. Mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell. Mitochondria and chloroplasts cannot grow outside their host cell. Evidence for this is based on the following: • Chloroplasts are the same size as prokaryotic cells, divide by binary fission, and, like bacteria, have Fts proteins at their division plane. The mitochondria are the same size as prokaryotic cells, divide by binary fission, and the mitochondria of some protists have Fts homologs at their division plane. • Mitochondria and chloroplasts have their own DNA that is c...

• Biology • Cells • Mitochondria and Chloroplasts Mitochondria and Chloroplasts All organisms need energy to perform vital processes and stay alive. That is why we need to eat, and organisms like plants gather energy from the sun to produce their food. How does the energy contained in the food we eat or in the sun get to every cell in an organism’s body? Fortunately, organelles called mitochondria and chloroplast do… Mitochondria and Chloroplasts • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • All organisms need energy to perform vital processes and stay alive. That ...