Structure of Mitochondria
The elaborate structure of mitochondria is very important to the functioning of the organelle.
Two specialized membranes encircle each mitochondrion present in a cell, dividing the organelle into a narrow intermembrane space and a much larger internal matrix, each of which contains highly specialized proteins. The outer membrane of a mitochondrion contains many channels formed by the protein porin and acts like a sieve, filtering out molecules that are too big. Similarly, the inner membrane, which is highly convoluted so that a large number of infolding called cristae are formed, also allows only certain molecules to pass through it
and is much more selective than the outer membrane.
To make certain that only those materials essential to the matrix are allowed into it, the inner membrane utilizes a group of transport proteins that will only transport the correct molecules. Together, the various compartments of a mitochondrion are able to work in harmony to generate ATP in a complex multi-step process.
The mitochondrion is different from most other organelles because it has its own circular DNA (similar to the DNA of prokaryotes) and reproduces independently of the cell in which it is found; an apparent case of endosymbiosis. Scientists hypothesize that millions of years ago small, free-living prokaryotes were engulfed, but not consumed, by larger prokaryotes, perhaps because they were able to resist the digestive enzymes of the host organism. The two organisms developed a symbiotic relationship over time, the larger organism providing the smaller with ample nutrients and the smaller organism providing ATP molecules to the larger one. Eventually, according to this view, the larger organism developed into the eukaryotic cell and the smaller organism into the mitochondrion.
Mitochondria are similar to plant chloroplasts in that both organelles are able to produce energy and metabolites that are required by the host cell, mitochondria are the sites of respiration, and generate chemical energy in the form of ATP by metabolizing sugars, fats, and other chemical fuels with the assistance of molecular oxygen. Chloroplasts, in contrast, are found only in plants and algae, and are the primary sites of photosynthesis. These organelles work in a different manner to convert energy from the sun into the biosynthesis of required organic nutrients using carbon dioxide and water. Like mitochondria, chloroplasts also contain their own DNA and are able to grow and reproduce independently within the cell.
Function of Mitochondria
The main function of the mitochondrion is the production of energy, in the form of adenosine triphosphate (ATP). The cell uses this energy to perform the specific work necessary for cell survival and function.
The raw materials used to generate ATP are the foods that we eat, or tissues within the body that are broken down in a process called catabolism. The breaking down of food into simpler molecules such as carbohydrates, fats, and protein is called metabolism. These molecules are then transferred into the mitochondria, where further processing occurs.
The reactions within the mitochondria produce specific molecules that can have their electrical charges separated within the inner mitochondrial membrane. These charged molecules are processed within the five electron transport chain complexes to finally combine with oxygen to make ATP. The process of the charged substances combining with oxygen is called oxidation, while the chemical reaction making ATP is called phosphorylation. The overall process is called oxidative phosphorylation. The product produced by this process is ATP.
Chloroplast
Chloroplasts are found in and that conduct . Chloroplasts absorb light and use it in conjunction with water and carbon dioxide to produce sugars, the raw material for energy and production in all green plants and the animals that depend on them, directly or indirectly, for food.
Chloroplasts capture to conserve in the form of and reduce to through a complex set of processes called photosynthesis. The word chloroplast is derived from the Greek words chloros which means green and plast which means form or entity. Chloroplasts are members of a class of organelles known as .
Structure of Chloroplast
Chloroplasts are observable morphologically as flat discs usually 2 to 10 micrometer in diameter and 1 micrometer thick. In land plants they are generally 5 um in diameter and 2.3 um thick. The chloroplast is contained by an envelope that consists of an inner and an outer phospholipids membrane. Between these two layers is the intermembrane space. A typical parenchyma (bulk of substance) cell contains about 10 to 100 chloroplast.
The material within the chloroplast is called the stroma, corresponding to the of the original bacterium, and contains one or more molecules of small circular DNA. It also contains , although most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast.
Function of Chloroplast
Their function is to produce glucose from carbon dioxide and water. To do this they need light energy.
Photosysnthesis actually takes place as two different sets of reactions. The "light reaction" requires light energy. Chlorophyll is required to convert light energy into chemical energy. This set of reactions produces two chemicals: ATP and NAHPH. In the "dark reaction" carbon dioxide and water are converted into carbohydrate. The dark reaction needs chemical energy which is supplied by ATP and NADPH.
Chloroplasts:
- Have a double membrane
- Have their own DNA
- Have their own ribosomes
- Make their own enzymes
- Are required for photosynthesis
- Contain chlorophyll.
Bibliography
Book: Molecules and Cells – John Adds, 2003
