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INTRODUCTION, 6 EUKARYOTIC CELLS, (5 PROKARYOTIC CELLS, o What makes an organism living? The answer to this is the, presence of the basic unit of life the cell in all living, organisms. All organisms are composed of cells., o Besides the nucleus eukaryotic cells have, other membrane bound structure called, organelles like ER, Golgi complex etc., o The eukaryotes include all the protists,, plants, animals and fungi. Plant cells have, large vacuole. Animals cells have, centrioles which are almost absent in plant, cells., o Ribosomes are of 80S (in cytoplasm)., Small subunit is 40S and large 80S., Cell Membrane, o Chemical studies on the cell membrane,, especially in human RBC enabled, scientists to deduce the possible structure, of plasma membrane., o Cell membrane is mainly composed of, proteins and lipids (mainly phospholipids)., o Phospholipids consist of polar head, (outward) and non-polar tail (hydrophobic), inner side. In human RBC 52% is proteins, and 40% lipids., o Membrane proteins can be integral or, peripheral., o Most accepted model for structure of cell, membrane is fluid mosaic model given, by Singer and Nicolson (1972)., o Membrane is selectively permeable. Many, molecules can move across the, membrane without any requirement of, energy is called passive transport., Movement of water by diffusion is called, osmosis. Many molecules require, energy/ATP for their transport called active, transport, e.g. Na /K' pump., o The quasi-fluid nature of lipid enables, lateral movement of proteins within the, overall bilayer. This ability to move within, the membrane is measured as its fluidity., o Polar molecules cannot move through the, non-polar lipid bilayer., o The fluid nature of membrane is important, for functions like cell growth, formation of, intercellular junctions, secretion,, endocytosis, cell division etc., Lack membrane bound cell organelles., o Are represented by bacteria, blue green algae, Mycoplasma or PPLO., o In addition to genomic DNA, many bacteria have small circular DNA outside, the genomic DNA called plasmids. Plasmid DNA confers certain unique, phenotypic characters to such bacteria. One such character is resistance to, antibiotics. Plasmid DNA is used to monitor bacterial transformation with, foreign DNA., o All prokaryotes have a cell wall surrounding the cell membrane (except, Mycoplasma)., Cell envelope and its modifications, Most prokaryotic cells have cell envelope, which is tightly bound three, layered structure., o The outermost glycocalyx followed by cell wall and then the plasma, membrane., 2 WHAT IS A CELL?, o Cell is the fundamental structural and functional unit of all, living organisms. Anything less than a complete structure of, a cell does not ensure independent living., Anton Von Leeuwenhoek first saw and described a live cell., 3 CELL THEORY, o In 1838, Matthias Schleiden, a German 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 the same time, Schwann (1839) a British, Zoologist, reported that animal cells had a thin layer called, plasma membrane. He concluded that plant cells have cell, walls. Schleiden and Schwann together formulated the cell, theory but this theory did not explain as to how-new cells are, formed., o Glycocalyx may be a loose sheath called slime layer or thick and tough called, capsule., o The cell wall prevents bacteria from bursting or collapsing., o Extension of plasma membrane into the cell in the form of vesicles, tubules, and lamellae are mesosomes. It helps in cell wall formation, DNA replication,, distribution of daughter cells, respiration, secretion process and increase the, surface area of plasma membrane., o In cyanobacteria, chromatophores contain pigments., o Each layer of the cell envelope performs distinct function, they act together as, a single protective unit. The plasma membrane is selectively permeable in, nature and interacts with the outside world. It is structurally similar to that of, eukaryotes., o Bacteria may be motile or non-motile. If motile they have flagella, composed, of three parts filament, hook and basal body., o Pili and fimbriae do not play role in motility., o Bacteria on the basis of the differences in the cell envelope can be Gram, positive or Gram negative., Ribosomes and inclusion bodies, o Ribosomes are 70S, has subunits 50S and 30S. Several ribosomes may, attach to a single mRNA and form a chain called polyribosome or, polysome., o Ribosomes are associated with plasma membrane., o The ribosomes of a polysome translate the mRNAinto proteins., o Rudolf Virchow explained that new cells arise from, pre-existing cells (Omnis cellula-e cellula) and finally, modified the cell theory as:, (i) All living organisms are composed of cells and products, of cells, (ii) All cells arise from pre-existing cells., AN OVERVIEW OF CELL, o Cells differ greatly in size, shape and activities for, example, Mycoplasma is smallest cell while egg of an, ostrich is the largest isolated single cell. Nerve cells are, some of the longest cells., • The cytoplasm is main arena of cellular activities in, both plant and animal cells., o Ribosomes are non-membrane bound organelles found in, both eukaryotic and prokaryotic cells. Apart from cytoplasm,, they are also found in mitochondria, chloroplast and on, rough ER., Animal cells contain another non-membrane bound, organelle called centrosome which helps in cell division., o Cells that have membrane bound nuclei are called, eukaryotic cells that lack a membrane bound nucleus called, prokaryotic cells., Inclusion bodies, Reserve material is stored in the form of inclusion bodies in prokaryotic, cytoplasm. Eg. phosphate granules, cyanophycean granules and glycogen, granules., Gas vacuoles are found in blue green and purple and green photosynthetic, bacteria.