Overview
All eukaryotic cells need a method to convert molecules into usable energy. Plant cells need a method to convert energy and nutrients taken in to sugars for food and structural building blocks. The method for the former is the mitochondria. The method for the latter is the chloroplast.
Mitochondria
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Chloroplast
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Membranes: The mitochondria (singular: mitochondrion) was most likely a free-floating prokaryote that entered into another cell through endosymbiosis. Therefore, it, like other early prokaryotes, has a double membrane. The outer membrane protects the mitochondrion from external damage, and covers the entire mitochondrion. The inner membrane provides the space for the actual ATP, the molecule used for energy in all life on Earth, to be synthesized. In order to provide the most surface area for synthesis of ATP to occur, the inner membrane is highly convoluted with folds called cristae.
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Membranes: The chloroplast was, like the mitochondria, once a free-floating prokaryote that entered another cell through endosymbiosis. It therefore has a double membrane, like other early prokaryotes. The outer and inner membranes of the chloroplast protect the interior of the organelle.
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Matrix: The mitochondrial matrix is the fluid-filled interior of the mitochondria. This is where one of the processes of ATP synthesis occurs; the krebs cycle. The krebs cycle releases many different products, most of which are electron carriers, that are used in the next process to produce large amounts of ATP.
DNA: Since the mitochondria was once a free-floating prokaryote, it has DNA separate from that of the rest of the cell. It, like all other prokaryotes, has DNA in a circle shape, rather than in a long strand. The mitochondrial DNA functions as normal DNA in the rest of the cell does; it provides genetic blueprints for the existence of the mitochondrion.
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Thylakoids and Associated Parts: The thylakoids are microscopic discs located within the chloroplast, organized in stacks called grana (singular: granum). They are connected through tubes called lamella, which allows for the exchange of fluid inside the thylakoids, known as lumen. The thylakoids contain the chlorophyll pigment that make photosynthetic plants green, and the thylakoid membrane is the site of the first part of photosynthesis: the light reaction.
Stroma: The chloroplast's stroma is the fluid-filled interior of the chloroplast, equivalent to the chloroplast's matrix. This is the site of the "dark reaction," the second part of photosynthesis that actually creates the G3P, which is subsequently used to create glucose for the plant.
DNA: Since the chloroplast was once a free-floating prokaryote, it has DNA separate from that of the rest of the cell. It, like all other prokaryotes, has DNA in a circle shape, rather than in a long strand. The chloroplast's DNA functions as normal DNA in the rest of the cell does; it provides genetic blueprints for the existence of the chloroplast.
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Mitochondria
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Chloroplast
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The mitochondria is responsible for synthesizing adenosine tri-phosphate, or ATP, the primary fuel for the cell, from glucose taken in by the cell. This process is known as cellular respiration, and occurs in many complex processes, most of which occur within the mitochondria.
Overall Reaction: C6H12O6 (glucose) -------> CO2 (waste) + H2O (waste) + ATP (energy) |
The chloroplast is responsible for synthesizing G3P, which is used as food for the cell, or as a structural component in strengthening the overall organism. The process of G3P synthesis is known as photosynthesis, and occurs in many complex processes.
Overall Reaction: H2O (water) + CO2 (carbon dioxide) -------> 2G3P (product) + O2 (waste) |
Glycolysis: The first process in cellular respiration is glycolysis. This occurs in the cytoplasm, the fluid filling the cell, outside of the mitochondria. In this process, glucose is broken down into two pyruvate molecules through a complex 10 step process. The pyruvate molecules then go on to the next process.
Grooming Phase: The second process in cellular respiration is a quick process known as the grooming phase. The exact location of this process is unknown; however, it is known that it occurs as the pyruvate is entering the matrix from the cytoplasm. This process turns the pyruvate molecules into molecules of Acetyl-coA, necessary in the next process.
Krebs Cycle: The third process in cellular respiration is the krebs cycle, which occurs in the mitochondrial matrix. This process synthesizes NADH (an electron carrier), small amounts of ATP, and CO2, (which is released). The products that are not released as waste go on to power the next phase of respiration.
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Light Reaction: The first process in photosynthesis is the light reaction, occurring in the thylakoid membrane. As made clear by the name, this reaction requires light. Photosystem II absorbs light energy, which excites the electrons. These electrons are passed onto an electron carrier, to a proton pump, and subsequently passed to photosystem I. The purpose of the electron transport chain in the light reaction is to create a concentration gradient that powers the synthesis of ATP.
Dark Reaction/Calvin Cycle: The second process in photosynthesis is the dark reaction, or, more formally, the calvin cycle. This reaction does not require light to occur. Carbon dioxide (CO2) taken in by the plant is catalyzed by an enzyme RUBISCO in a series of complex reactions that synthesizes G3P. The G3P is then released, and can be further converted to whatever carbohydrate the plant may need.
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ETC: The final process in cellular respiration is the electron transport chain, occurring in the cristae of the inner membrane of the mitochondria. The energy from the electrons brought over by NADH is used to pump protons from the matrix to the intermembrane space of the mitochondria. This creates a concentration gradient; the protons "want" to reenter back into the matrix. A membrane channel known as ATP synthase allows for the protons to reenter the matrix. As they are reentering, their kinetic (movement) energy is used to power the synthesis of large amounts of ATP, which can then be used in whatever process the cell needs.
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