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Living Cell

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  LIVING CELL Introduction The cell is the basic structural and functional unit in all living organisms. Living forms vary in size but they are all made up of cells. In unicellular organisms, the cell is the organ. As an organism grow in complexity, the cells increase in number and similar cells aggregate into tissues and organs with specialized functions. The shape of the cell is often determined by its function and the size of the cell is determined by the optimum dimensions that will enable it to perform its duties more effectively . The human body is composed of a multiple of specialized tissues which inturn consist of vast clusters of cells differentiated into specialised chemical factories which perform various biochemical reactions. Types of cells Two general types are recognised in nature. They are prokaryotic and eukaryotic cells. Prokaryotic cells Prokaryotes were the first cells to arise in biological evolution. They are very small and simple having only a single membrane. T
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Types of Living cells

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  Types of cells Two general types are recognised in nature. They are prokaryotic and eukaryotic cells. Prokaryotic cells Prokaryotes were the first cells to arise in biological evolution. They are very small and simple having only a single membrane. The cell membrane, is usually surrounded by a rigid cell wall. They are devoid of nucleus and membranous organelles such as mitochondria and endoplasmic reticulum etc. (Fig. 1.1). Eukaryotic cells Eukaryotic cells are presumably derived from prokaryotes. They are much larger and much more complex than prokaryotic cells (Fig. 1.2). They have nucleus and membrane bound subcellular organelles. Many of their metabolic reactions are segregated within structural compartments. The significant differences between prokaryotic and enkaryotic cells are: The eukaryotic cell structure is composed of (i) cell membrane, (ii) nucleus (iii) mitochondria (iv) endoplasmic reticulum (v) golgi apparatus (vi) ribosomes (vii) lysosomes and others. These speciali
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Sub cellular Organelles

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  Sub cellular Organelles   Cell Membrane The cell is enveloped and thus separated from its surroundings by a thin wall contains a rigid framework of polysaccharide chains crosslinked with short peptide chains. Its outer surface is coated with lipopolysaccharide. Cell membrane is also called as plasma membrane (or) plasma lemma. The pili, not found in all bacteria have extensions of the cell wall. The cell membrane contains about 45% lipid and 55% protein. The cell membrane or plasma membrane have an average thickness of 75A°. The principal lipids are phospholipids, sphingolipids and cholesterol. An important feature of these lipids is they are composed of hydrophobic (water - insoluble) hydrocarbon sections and hydrophilic (water soluble) units. The latter include charged units (eg. phosphate or amino groups) and uncharged units (eg. hexose). In water, such compounds orient themselves in such a way that only the hydrophilic section is exposed to water. The hydrophobic components of in
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Cell Membrane and its Functions

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  Cell Membrane The cell is enveloped and thus separated from its surroundings by a thin wall contains a rigid framework of polysaccharide chains crosslinked with short peptide chains. Its outer surface is coated with lipopolysaccharide. Cell membrane is also called as plasma membrane (or) plasma lemma. The pili, not found in all bacteria have extensions of the cell wall. The cell membrane contains about 45% lipid and 55% protein. The cell membrane or plasma membrane have an average thickness of 75A°. The principal lipids are phospholipids, sphingolipids and cholesterol. An important feature of these lipids is they are composed of hydrophobic (water - insoluble) hydrocarbon sections and hydrophilic (water soluble) units. The latter include charged units (eg. phosphate or amino groups) and uncharged units (eg. hexose). In water, such compounds orient themselves in such a way that only the hydrophilic section is exposed to water. The hydrophobic components of individual molecules tend to
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Cell Wall and its Functions

  Cell Wall Plant and bacterial cell membranes are surrounded by a thick cell wall. Bacterial cell wall The bacterial cell is enclosed within a wall that differs chemically from the cell wall of plants. The cell wall contains a rigid framework of polysaccharide chain cross linked with short peptide chains and its outer surface is coated with lipopolysaccharide. The pili, found in some bacteria are extensions of the cell wall. In some bacteria the cell wall is surrouned by an additional structure called a capsule. The cell wall and capsule confer shape and form of the bacteriam and also act as a physical barrier to the cell membrane. In the absence of cell wall and capsule is mechanically fragile and the bacteria would rupture. Plant cell wall The cell wall is a thick polysaccharide containing structure immediately surrounding the plasma membrane. In multicelllar plants, the plasma membrane of neighboring cells are separated by these walls, and adjacent plant cell have their walls fused
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Nucleus and its Functions

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  Nucleus Nucleus is the heaviest particulate component of the cell. Except matured mammalian erythrocytes, nucleus is found in almost all cells. The nucleus about 4-6 µ m in diameter is surrounded by a perinuclear envelope. At various position the outer membrane of the envelope fuses with the inner membrane to form pores (Fig. 1.4). Nuclear pores provide continuity between the cytosol and the contents of the nucleus (nucleoplasm). The electron microscope reveals that the nuclear content consist of granular or fibrillar structures. The nucleolus, a discrete body within the nucleus, contains ribonucleic acids (RNA). The most important component of the nucleus is an organised clumps of threadwork known as chromatin which is distributed throughout the nucleus and contains most of the cellular deoxy ribonucleic acids (DNA). Immediately before the cell division the chromatin organises into simple thread like structures known as chromosomes which will eventually be distributed equally to eac
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Mitochondria and its Functions

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  Mitochondria These are the largest particulate components of the cytoplasm and represent upto 15% -20% of the dry weight of the cell. They vary in shape (spherical, filamentous, sausage shaped) and size (0.5 to 3μ long 0.1 to 0.6μ wide).The number varies with the size and energy requirements of the cell. For eg. flight muscles in birds contain rich amount of mitochondria when compared to any other parts of the body Electron microscopic studies show that a mitochondrion has two membranes inner and outer which are separated from each other by 50 to 100oA. The outer and inner membranes differ in lipid composition and in enzyme content. The inner membrane is very much folded to form shelf - like structures of varying width. These shelf - like structures, known as internal ridgs or cristae, extent into matrix of the mitochondrion structure. Thus two structurally different space can be distinguished, the intracristae space and the matrix space (Fig. 1.5). The matrix space is rich in enzyme
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