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Jr |11th class BOTANY VOL-3 CELL - THE UNIT OF LIFE 1 8 CELL - THE BASIC UNIT OF LIFE NEET SYLLABUS  Cilia and flagella  Centrosomes and centrioles  Nucleus  Chromosomes  Microbodies CONTENTS  Introduction  What is a cell  Cell theory  An over view of cell  Prokaryotic cell (a) Cell envelope and its modifications (b) Ribosomes and inclusion bodies  Eukaryotic cell  Cell membrane  Cell wall  Endomembrane system (a) Endoplasmic reticulum (b) Golgi apparatus (c) Lysosomes (d) Vacuoles  Mitochondria  Plastids  Ribosomes  Cytoskeleton ACTIVE SITE EDUTECH - 9844532971(FOR CUSTOMIZED PRINTED BOOKS WITH LOGO & NAME)
Jr |11th class BOTANY VOL-3 2 CELL - THE UNIT OF LIFE INTRODUCTION As we konw all living organisms are made up of cells and their produces. Study of structure and composition of cell is known as Cytology. Cell Biology correlates the structure with the function ( life processes) of cells. All organisms are made up of cells, whether unicellular or multicellular. Cell is the basic structural/fuctional unit of an life. Life exists in the form of cell. INTRODUCTION ABOUT G.N.RAMCHANDRAN(1922-2001) * G.N.Ramachandran, an outstanding figure in the field of protein structure. * He was the founder of the ‘Madras school’ of conformational analysis of biopolymers. * He discovered triple helical structure of collagen and published in ‘Nature’ (science journal) * His analysis on conformations of proteins through ‘Ramachandran’s plot rank’ is the most out standing contribution in structural biology. * He was deeply influenced by Linus Pouling publication on models of á- helix and â - sheet structure that directed his attention into solving the structure of Collagen. WHAT IS A CELL * All organisms are composed of cells. Some are composed of a single cell and are called unicellular organisms while others, like us, composed of many cells, are called multicellular organisms. * Unicellular organisms are capable of (i) independent existence (ii) performing the essential functions of life. * Anything less than a complete structure of a cell does not ensure independent living. Hence, cell is the fundamental structural and functional unit of all living organisms. * First cell discovered by - Robert Hook in Cork cells of Oak (Quercus suber) tree. * Anton Von Leeuwenhoek first saw and described a living cell. * Robert Brown discovered the nucleus.  Corti and Fontona discovered the presence of jelly like substance in the cell.Dujardin named it as ‘Sarcode’ and Purkinje renamed the sarcode as‘protoplasm.’  Huxly - Protoplasm is ‘Physical basis of life’ * The invention of the microscope and its improvement leading to the electron microscope (knoll and Rusca) revealed all the structural details of the cell. CELL THEORY (CELL DOCTRINE): * In 1838, Matthias Schleiden, a botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. At about the same time, Theodore. Schwann (1839), Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is today known as the ‘plasma membrane’. He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character of the plant cells. * Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells. ACTIVE SITE EDUTECH - 9844532971(FOR CUSTOMIZED PRINTED BOOKS WITH LOGO & NAME)
Jr |11th class BOTANY VOL-3 CELL - THE UNIT OF LIFE 3 * Schleiden and Schwann together formulated the cell theory. This theory however, did not explain as to how new cells were formed. * Rudolf Virchow (1855) (CELL LINIAGE THEORY OR CELL INHERITANCE THEORY) first explained that cells divide and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. Cell theory as understood today is: (i) All living organisms are composed of cells and products of cells. (ii) All cells arise from pre-existing cells.  Cell theory is not applicable to acellular structures like virus AN OVERVIEW OF CELL * The onion cell which is a typical plant cell, has a distinct cell wall as its outer boundary and just within it is the cell membrane. * Cells that have membrane bound nuclei are called eukaryotic whereas cells that lack a membrane bound nucleus are prokaryotic. * In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell. * The cytoplasm is the main arena of cellular activitiesin both the plant and animal cells. Various chemical reactions occur in it to keep the cell in the ‘living state.’ * Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles like the endoplasmic reticulum (ER), the golgi complex, lysosomes, mitochondria , microbodies. The prokaryotic cells lack such membrane bound organelles. * Ribosomes are non-membrane bound organelles found in all cells – both eukaryotic as well as prokaryotic cell. Within the cell, ribosomes are found not only in the cytoplasm but also within the two organelles – chloroplasts (in plants) and mitochondria and on rough ER. * Animal cells contain another non-membrane bound organelle called centriole which helps in cell division. SIZE AND SHAPE OF CELL Cell differ greatly in size, shape and activites. * Mycoplasma (Smallest cells) : Only 0.3m in length [PPLO (pleuro pneumonia like organisms) is a type of mycoplama having the size about 0.1m )] * Bacteria = 3 to 5 m in length and 1-2 m in diameter virus = 0.02-0.2 m * Largest isolated single cell = egg of an ostrich. Typical eukaryotic cell = 10-20 m * Human red blood cell = 7.0 -m in diameter * Nerve cell = longest cell Shape : * The shape of the cell may vary with the funtion they perform. * They may be disc-like, polygonal, columnar, cuboid, thread like or even irregular. * The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms). They are generally smaller and multiply more rapidly than the eukaryotic cells. ACTIVE SITE EDUTECH - 9844532971(FOR CUSTOMIZED PRINTED BOOKS WITH LOGO & NAME)
Jr |11th class BOTANY VOL-3 4 CELL - THE UNIT OF LIFE Cell Organization Depending upon origin, cells are of three types: (a) Prokaryotic cell (b) Mesokaryotic cell (c) Eukaryotic cell (a) Prokaryotic cell: e.g. bacteria, cyanobacteria, archaebacteria, Mycoplasma, Rickettsiae. * Size - 0.1 – 5μ; Volume 0.2 – 10 μm3; DNA : RNA ratio - 1 : 2.  They have only one envelope system. Membrane bound cell organelles are absent. Well defined nucleus absent. The clear nuclear area shows a tangled DNA called as nucle- oid/genophore /prochromosome. * Circular DNA is not associated with histones.  Amount of DNA remains constant throughout the life cycle.  Spindle apparatus not formed during cell division. * Cell membrane may be folded to form mesosome that acts as site of respiration. * Flagella if present are single-stranded. * Ribosomes typically of 70S type. STRUCTURE OF BACTERIAL CELL The structure of a general bacterial cell is shown: (1) Nucleoid * There is no distinct nucleus with a nuclear membrane. * The bacterial genome is a single circular double helical DNA molecule., DNA is not bound by histones. * Due to the absence of a well-organised distinct nucleus, the genetic material is called nucleoid. * In some bacteria “extra” pieces of circular naked dsDNA are also found. These are called plasmids. White blood cells (amoeboid) Columnar epithelial cells (long and narrow) Red blood cells (round and biconcave) A tracheid (elongated) Mesophyll cells (round and oval) Nerve cell (Branched and long) Figure 1 : Diagram showing different shapes of the cells ACTIVE SITE EDUTECH - 9844532971(FOR CUSTOMIZED PRINTED BOOKS WITH LOGO & NAME)