Cell is the smallest unit of living tissue and it is a structural and functional unit of living things. Cell of different tissue perform different functions. It may be flattened, cubical, columnar, fusiform, pyramidal or flask shape.
Most cells are composed of protoplasm : A mixture of carbohydrates, lipids,proteins,nucleic acids, inorganic salts,gases and between 70–80%water.
There are three major parts of cell:
1. Plasma Membrane: It forms the water boundry of the cell and separate it from adjacent cell and external environment.
It transports the substances into an out of the cell. Its thickness majors amount 70 Angstrom.
2. Nucleus: It is the largest structure present almost in the center of cell. It is more or less spherical in shape. It contains most of the cells genetic material, organic and multiple long linear DNA molecules with a large variety of proteins.
3. Cytoplasm: It is the region line between the cell membrane and nucleus. The cytoplasm contains cell organelles like Endoplasmic reticulum, mitochondria, golgi bodies, lysosomes, centrosome and centriole etc.
A) Endoplasmic reticulum: It consist of a system with intercommunicating membranes sacs and exist in two forms.
1. Rough Endoplasmic reticulum:
It contains ribosomes. The ribosomes are the sites of protein synthesis.
2. Smooth Endoplasmic reticulum: They does not contains ribosomes. This type of Endoplasmic reticulum is consult with fatty acid and steroids. They store and release calcium.
B) Ribosomes: They appear as dense rounded granules lying single or in dense cluster in the cytoplasm in the form of spirals or may be attached to endoplasmic reticulum. They are composed of ribonucleoprotein and sites of protein synthesis.
C) Golgi bodies: This is a system of sac arranged as stock of coins and the cycles like Endoplasmic reticulum but with no ribosomes attached to it. They transfer materials synthesised by the ribosomes at the endoplasmic reticulum to the cell surface. The parts of gogli bodies that contains newly manufactured materials brokes away from the best part of it and pass towards the surface of cell at secretion granules.
D) Mitochondria: They are rod like bodies bounded by a double layered membrane. They occur in the cytoplasm at variable numbers about few hundred to few thousands. An outer layer which is smooth and an inner layer folded into finger like structures or tubules called cristea. Both these layers in close a central cavity called matrix. The Mitochondria are made up of proteins, phospholipids and some ribonucleic acid. They also contain some important enzymes systems. The Mitochondria provide the metabolic energy to the cell by generating ATP( Adenosine tri phosphate) therefore Mitochondria is also known as power house of the cell.