Mitochondria function in animal Cell
1.3.5 Mitochondria (Gk. mitos: thread, chondroitin: granules)
Mitochondria (Singular mitochondrion, Powerhouse of the cell) look like small threads or granules either spherical or elongated. It is a self-replicating organelle. Altman (1890) established them as cell organelles and called them bioblast. The term mitochondria was given by C. Benda (1898).
Size:- The diameter of mitochondria is 0.2-1μm while the length is one um to 4.1μm. Their numbers are few to many thousand per cell, depending upon the physiological activity of the cell.
Chondriome:- All the mitochondria present in a cell are collectively called chondriome. Usually, animal cells have more mitochondria than plants.
Structure:- It is a double membrane structure. The outer membrane is smooth while the inner membrane is folded. If the outer membrane of mitochondria is removed then it is called a mitoplast. The folds of the inner membrane are known as cristae which increase the surface area for chemical reactions. These cristae contain (bear) pin head particles called oxysomes elementary particles or F1 particles. Inside the inner membrane, a fluid is present called a matrix.
The matrix contains enzymes for cellular aerobic respiration, proteins, 70s ribosomes, RNA and double-stranded circular DNA. (It is 1% of the total DNA of the cell.) This DNA can code the synthesis of some types of proteins.
Function of Mitochondria:
They provide a site for aerobic respiration. Most of the oxidative metabolism and ATP production occurs in mitochondria. Therefore mitochondria are called powerhouses of the cell.
Mitochondria also help in vitellogenesis (Yolk formation) in oocytes.
1.3.6 Plastids
The plastid (Gk. Plastos: formed, moulded) is a major double membrane organelle found in plant cells. Plastids are the sites of manufacture and storage of important chemical compounds used by cells. pigments that can change or determine the cell colour for different purposes. Plastids are classified into chloroplasts, chand leucoplasts. All types of plastids are formed from a precursor molecule.
Chromoplasts:
photosynthesis these are pigmented plastids located in colourful (other than green) parts of plants like petals and fruit covering. These plastids also help in cross-pollination. These also contain very small amounts.
Leucoplasts:
These are colourless plastids present in colourless parts of plants like roots, woody stems etc. They are triangular in shape. They help in the storage of food. e.g., amyloplast which stores starch, Elaioplast which stores lipids and proteinoplast which stores protein.
Chloroplast:
These are green plastids, present in green parts of plants like leaves, herbaceous stems, unripened fruit coverings etc.
They are double membrane structures. The outer membrane is smooth and more permeable while the inner membrane is less permeable. The inner membrane contains a disc-like structure called thylakoid and a group of thylakoids stacked together is called granum (plural Grana).
There are many grana in a chloroplast and many chloroplasts in a cell (up to 40). The fluid which surrounds grana is called stroma. The stroma contains enzymes required for the synthesis of carbohydrates during dark reactions of photosynthesis.
The most abundant and important enzyme is Rubisco (about 16% of chloroplast), The stroma also contains a small amount of DNA and, a semiautonomous organelle of cells like mitochondria. RNA and 70s ribosome. The presence of these substances indicates that it is
The grana are connected to each other by a long thylakoid membrane called lamellae. The chloroplast is the site for photosynthesis.
The light reaction takes place in grana which contains a large number of photosynthetic pigments in a chloroplast originating from cyanobacteria through the endosymbiotic process. organized manner, while the dark reactions occur in stroma.
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