Mitochondria

Mitochondria hold DNA (likely because of evolutionary leftovers) and this DNA is directly inherited from the mother, meaning that it is an exact match to the mother's DNA. This type of DNA is used in forensics from time to time. Otherwise, mDNA serves no other purpose, and we likely won't even have it in a few million years. Even more interesting is the fact that Mitochondria contain DNA which is not ours! Put simply at some point in the distant past of human evolution; way in the past: at a point when we ourselves where very simple organisms. We formed an endosymbiotic relationship with a proto-bacteria for mutual benefit. This proto-bacteria - apparently related to the Rickettsia which still exits - then became permanent whithin every cell, providing energy but losing some independent features whilst retaining to this day it's own DNA. The Mitochondria have been described as "The Warp-Core of the cell" This is a more detailed explanation of what little is known about this fascinating yet generally unknown story of human development: That we are in fact a walking collection of symbiotic organisms!

Mitochondria have many features in common with prokaryotes. As a result, they are believed to be originally derived from endosymbiotic prokaryotes. A mitochondrion contains DNA, which is organized as several copies of a single, circular chromosome. This mitochondrial chromosome contains genes for redox proteins such as those of the respiratory chain. The CoRR Hypothesis proposes that this Co-location is required for Redox Regulation. The mitochondrial genome also codes for some RNAs of ribosomes, and the twenty-two tRNA's necessary for the translation of messenger RNAs into protein. The circular structure is also found in prokaryotes, and the similarity is extended by the fact that mitochondrial DNA is organized with a variant genetic code similar to that of Proteobacteria.[36] This suggests that their ancestor, the so-called proto-mitochondrion, was a member of the Proteobacteria.[36] In particular, the proto-mitochondrion was probably related to the rickettsia.[37] However, the exact relationship of the ancestor of mitochondria to the alpha-proteobacteria and whether the mitochondria was formed at the same time or after the nucleus, remains controversial.[38] The ribosomes coded for by the mitochondrial DNA are similar to those from bacteria in size and structure.[39] They closely resemble the bacterial 70S ribosome and not the 80S cytoplasmic ribosomes which are coded for by nuclear DNA. The endosymbiotic relationship of mitochondria with their host cells was popularized by Lynn Margulis.[40] The endosymbiotic hypothesis suggests that mitochondria descended from bacteria that somehow survived endocytosis by another cell, and became incorporated into the cytoplasm. The ability of these bacteria to conduct respiration in host cells that had relied on glycolysis and fermentation would have provided a considerable evolutionary advantage. In a similar manner, host cells with symbiotic bacteria capable of photosynthesis would also have had an advantage. The incorporation of symbiotes would have increased the number of environments in which the cells could survive. This symbiotic relationship probably developed 1.7[41]-2[42] billion years ago. A few groups of unicellular eukaryotes lack mitochondria: the microsporidians, metamonads, and archamoebae.[43] These groups appear as the most primitive eukaryotes on phylogenetic trees constructed using rRNA information, suggesting that they appeared before the origin of mitochondria. However, this is now known to be an artifact of long-branch attraction - they are derived groups and retain genes or organelles derived from mitochondria (e.g., mitosomes and hydrogenosomes).[1]

This is from Mitochondrian WIKIPEDIA

As it is a main site of respiration and energy of the cell, it is located in the cytoplasm (of the cell).
Answer:

They are located in Cells, the building blocks of life.

Mitochondria:-

The mitochondria are dynamos encased inside double membranes. The outer one communicates with the cell, and the inner membrane contains machinery capable of converting food (glucose) to adenosine triphosphate (ATP), a chemical form of energy. Mitochondria are small, colorless, filamentous or tubular, granular structures present in the cytoplasm of all eukaryotic cell (except Mammalian RBC and sieve tube of Phloem). They are the site of cellular respiration and contain enzymes that involve in the breaking down of complex organic substances into simpler inorganic substances with the liberation of energy in the form of ATP. Thus, they are known as the Power House of the cell.

Size:- They are 1.5 to 10 µm in length, 0.25 to 1 µm in breadth and about 1 µm in diameter.

Shape:- The shape of mitochondria is determined by the physiological condition of cell. The shape may be oval, spiral, cylindrical, sausage shaped or filamentous.

Structure:- Mitochondria are rod-shaped structures and are double membrane bound cell organelles consisting of outer and inner membrane. The membranes are made up of phospholipids and proteins. The space between two membranes is known as Perimitochondrial space, which has the same composition as the cytoplasm of the cell. However, the protein content in this space differs from that in the cytoplasm. The structure of Mitochondria can be described as below:

Outer Membrane: The outer membrane is smooth and has almost the same amount of phospholipids as proteins. It has a large number of special proteins. The outer membrane is completely permeable to nutrient molecules, ions, ATP and ADP molecules.

Inner Membrane:

The inner membrane is more complex in structure as it contains the complexes of the electron transport chain and the ATP synthesizing complex. It is permeable only to oxygen, carbon dioxide and water. It is made up of a large number of proteins that play an important role in producing ATP, and also helps in regulating transfer of metabolites across the membrane. The inner membrane is thrown into a number of pegs like projections towards inner side and has infoldings known as Cristae. The Cristae and inner membrane contains a number of tennis racket like structures known as Oxysome or Elementary particlesor F1 particles. They are the site of respiration. The inner membrane encloses matrix of fluid, which contain circular DNA, RNA, Ribosome, amino acids, proteins and enzymes.

Matrix:

The matrix is a complex fluid mixture of enzymes that are enclosed by inner membrane. It is important for the synthesis of ATP molecules, special mitochondrial ribosome, TRNAs, the mitochondrial DNA, proteins and enzymes. Besides these, it has oxygen, carbon dioxide and other recyclable intermediates.

Mitochondria are self-duplicating cell organelles. They are commonly known as Semi-autonomous cell organelles because they contain machinery (DNA, RNA) for protein synthesis. However, they partially depend on nuclear DNA for performing other functions.

Functions of mitochondria:-

1. The complete oxidation of organic food material into simple inorganic substances (carbohydrates, fats, etc.) with the liberation of energy in the form of ATP takes place in Mitochondria. The entire process of liberation of energy in the form of ATP that occurs in mitochondria is known as oxidative phosphorylation. As well as they help in other metabolic activities of the cell. Thus, they are known as the Power House of the cell.

2. They help in the synthesis of amino acid (such as; Glutamic acid, Aspartic acid, etc.), fatty acid, hemoglobin and hormones (like testosterone and estrogen).

3. They provide intermediate for the synthesis of Chlorophyll, Pyrimidine (nitrogen base), Steroids, Cytochromes and Alkaloids (complex organic substance and nitrogen containing bases found in the roots of medicinal plants).

4. They help in balancing calcium-ion concentration in a cell.

5. They forms middle piece of sperm.

6. They help in the development of yolk during ovum formation.

7. They play an important role in the process of programmed cell death. Unwanted and excess cells are pruned away during the development of an organism. The process is known as apoptosis. Abnormal cell death due to mitochondrial dysfunction can affect the function of the organ.
In cells.

its part of it

It carry out respiration.It is essential for energy production

Well, as you know, the mitochondria are the producers of most of a cell's energy and the nucleolus creates ribosomes. The cell wall is only in a plant cell and is a rigid layer of non-living material that surrounds the cells of plants and some organisms.

An analogy can be written in the form: this is to that, as this(2) is to that(2).

Here are some possible analogies for mitochondria in cells:

• The fuel cell in a hydrogen/electric powered automobile (good analogy because the fuel cell is performing a function in the car in a way very similar to the mitochondrion in a cell) -- fuel cell : automobile mitochondria : cell
• the power plant for a town -- power plant : town :: mitochondrion : cell
• I would think of it as some sort of power plant. Anything that produces energy.
• I was told once by a teacher to think of the mitochondria as red bull. Just as red bull provides the body "wings" or energy, the mitochondria provides energy for the cell.
• Or you can liken it to the fuel feeding a boiler or electrical supply to a company.
• It is like a gas tank, "fuels" up what you want.