TEST PORTIONS.pptx

INTERNAL PORTIONS CELL STRUCTURE & FUNCTIONS STEM CELLS, TYPES & FUNCTIONS Structure and function of a cell Cell All living forms are composed of microscopic units called as “Cells”. A cell is the basic structural and functional unit of all life forms. Study of structure and compos...

INTERNAL PORTIONS CELL STRUCTURE & FUNCTIONS STEM CELLS, TYPES & FUNCTIONS Structure and function of a cell Cell All living forms are composed of microscopic units called as “Cells”. A cell is the basic structural and functional unit of all life forms. Study of structure and composition of cell is called as “Cytology”. Cell was first observed by “Robert Hooke” in a dead cork slice in the year 1665. The word cell was derived from a Greek word “Cellulae” which means small room.  First living cell was discovered by A.V. Leeuwenhoek. Protoplasm is physical basis of life Protoplasm is an aggregate of water, ions, salts and other organic molecules like proteins, carbohydrates, fats, nucleic acids, vitamins etc. Types of cell & Organism (a) On the Basis of Number of Cells, Organisms can be categorized as: (i) Unicellular organisms: o These are organisms which made up of single cell only. o This single cell performs all the vital body functions of an organism. e.g. Amoeba (i) Multicellular organisms: o These are the organisms which made up of numerous cells. o These cells then combine to form an organ and group of organs performing different functions forms an organ system which further forms an organism. e.g. Plants and animals (b) On the basis of type of organization, cells are two types : (i) Prokaryotic cells: o These are primitive and incomplete cells. o They have less developed nucleus without nuclear membrane & nucleolus. e.g. Bacteria. (ii) Eukaryotic cells: o These are well developed cells. o They have advanced nucleus with unclear membrane and nucleolus. e.g. Plants & animals. Difference between Prokaryotic cell and Eukaryotic cell PROKARYOTIC CELL EUKARYOTIC CELL o Incipient nucleus, o True nucleus, o No nuclear membrane, o Nucleolus & Nuclear membrane o Nucleolus absent, No mitosis, present Mitosis presence of histones absent histones in chromosome o Organelles absent o Present o Ribosomes-80S type o Ribosomes-70S type o DNA circular o DNA (linear) Cell Shape o Cells are of variable shapes and sizes. o Their shape is according to the function. o Generally cells are spherical but they may be elongated (nerve cell), branched (pigmented), discoidal (RBC), spindle shaped (muscle cell) etc. Cell size Size of cell is variable, microscopic, Macroscopic. Size may vary from 0.2 µm to 18 cm. Size of a typical cell in a Multicellular organism ranges from 20-30 mn. The largest cell is ostrich egg (15 cm. in dia with shell & 8 cm. in dia without shell) The longest cell is nerve cell. Smallest cells so far known are PPLOs e.g. Mycoplasma (0.1 µm in dia.) Components of Cell There is an occurrence of division of labor within a cell as they all got certain specific components called “Cell organelles” each of them perform a specific function. The three basic components of all the cells are (i) Plasma Membrane) (ii)Organelles (iii) Cytoplasm Cell membrane Cell membrane is also called as plasma Membrane It is the limiting boundary of cell which separates the cytoplasm from its surroundings. It is found in both plant as well as animal cells. It is the outer most covering of a cell in case of animals and lies below the cell wall in case of plants.  It is made up of proteins and lipids where proteins are sandwiched between bilayer of lipids. Selectively permeable in nature. It permits the entry and exit of some materials in and out of the cell. Singer and Nicholson gave the fluid mosaic model of plasma membrane according to him it consists of a protein layer sandwiched between two layers of lipids. Function of plasma membrane: It regulates the movement of molecules inside and outside the cell. It helps in maintaining the distinct composition of the cell. Transportation of molecules across the plasma membrane (b) Cell Wall: It is the outermost covering of the plant cells It is absent in animal cells. Cell wall is rigid, strong, thick, porous and non living structure. It is made up of cellulose and hemicelluloses. Cell walls of two adjacent cells are joined by a layer called middle lamellae. It is made up of calcium and magnesium pectate. Functions of cell wall: It provides definite shape to the cell. It provides strength to the cell. It is allows entry of molecules of different sizes. It is antigen specific. It has the characteristics of repair and regeneration Nucleus The most important cell organelle which directs and controls all its cellular activities. It is called as “Headquarter of the cell”. It was discovered by “Robert Brown in 1831”. In eukaryotes a well defined nucleus is present while in prokaryotes a well defined nucleus is absent. Prokaryotes contain a primitive nucleus.  It has double layered covering called as nuclear membrane. Nuclear membrane has pores which regulate the movement of materials of materials in & out of the cell. Nucleus also contains nucleolus and chromatin material Chromosomes or chromatin material consists of DNA which stores and transmits hereditary information for the cell to function, grow and reproduce. i) Function of the nucleus: It controls all the metabolic activities of the cell and regulates the cell cycle. It helps in transmission of hereditary characters from parents to off springs Cytoplasm Cytoplasm was discovered by Kolliker in 1862. It is the site of both biosynthetic and catabolic pathways. It can be divided into two parts: (i) Cytosol: Aqueous soluble part contains various fibrous proteins forming cytoskeleton. (ii) Cell organelles: Living part of the cells having definite shape, structure and function bounded by plasma membrane. Endoplasmic reticulum It is the network of membranes present in the cytoplasm. It was discovered by Porter, Claude and Fullam. These are present in all cells except prokaryotes and mammalian erythrocytes. They are made up of three components: (i) Cistemae: These are long, flattened, parallelly arranged, unbranched tubules. They are active in protein synthesis. (a)Types : Endoplasmic reticulum is of two types Smooth ER Rough ER Made of tubules mainly. Made of cisternae and vesicles Helps in steroid, lipids and Helps in protein synthesis. Polysaccharide synthesis. It Contains ribosomes on its Ribosomes are absent. surface. Helps in membrane biogenesis. Function of ER: Transport of materials between various regions of cytoplasm and between cytoplasm and nucleus. It also function as a cytoplasmic framework for biochemical activities. It forms endoskeleton of cell. It helps in synthesis of fats, steroids, cholesterol etc. It contains secretory proteins. SER plays a crucial role in detoxification of drugs and poisonous Golgi apparatus Golgi apparatus consists of single membrane membrane bounded vesicles arranged parallel to each other in stacks called Cisternae along with some large and spherical vacuoles. It was discovered by Camilo Golgi. It is absent in prokaryotes, mammalian RBC’s & sieve cells. Functions: It helps in formation of lipids It helps in formation of middle lamellae It is secretary in nature. It helps in melanin synthesis Lipids and proteins synthesized in endoplasmic reticulum are packed at Golgi complex. Mitochondria It is a rod shaped structure found in cytoplasm of all eukaryotic cells except mammalian RBC’s. These are also absent in prokaryotes. It was first seen by Kolliker in insect cells. Maximum mitochondria are found in metabolically active cells. It is also called as “Power House of the Cell” It is double membranous structure Inner membrane is folded inside to from chambers called Cristae.  ”Cristae” are the infoldings of inner mitochondrial membrane that possess enzymes for respiratory cycles like Kreb Cycle. ATP synthesizing units are called Oxysomes or F1 particles. Space between inner and outer mitochondrial membranes is called as peri mitochondrial space. The fluid present in mitochondrial is called as matrix. Functions: Its main function is to produce and store the energy in the form of ATP. It is the site of Kreb cycle of respiration. Ribosomes The sites of protein synthesis. All structural and functional proteins (enzymes) coded by the nuclear DNA, are synthesized upon cytoplasmic ribosomes. The DNA codes are transcripted into messenger RNA (mRNA) molecules in the chromosomes of the nucleus. mRNA molecules diffuse out into the cytoplasm and each becomes attached to several ribosomes which thus from a group called polyribosome. Plastid It is double membranous discoidal structure, found only in plant cells. The term plastid was given by Haeckel. Chloroplast have following two Parts : (i) Stroma: It is a granular transparent substance also called as matrix. Grana are embedded in it. They also contain lipid droplets, starch grains, ribosomes etc Function: This is the site of dark reaction of photosynthesis. (ii) Grana: It constitutes the lamellar system. These are found layered on top of each other, these stacks are called as Grana. Each granum of the chloroplast is formed by superimposed closed compartments called Thylakoids. Function: They are the sites of light reaction of photosynthesis In each thylakoid Quantasomes are present which are called as Photosynthetic units. Vacuoles These are membrane bounded regions in the cytoplasm containing water and other substances. They are bounded by a single membrane called Tonoplast. In animal cells vacuoles are smaller in size and numerous while in plant cells a single large vacuole is found which occupies about 90% of the volume of cell. Functions: It helps in maintaining osmotic pressure in a cell. It stores toxic metabolic products of plant cell. It contains various Colored pigments like anthocyanins. Lysosomes Discovered by: Christian de Duve) (Lyso = digestive, some = body) These are tiny sac like granules containing enzymes of intracellular digestion. They are single membrane bounded organelles present only in animal cells. They contain hydrolyzing enzymes called acid hydrolyses. Function : Their main function is phagy = digestion They are kind of waste disposal system. They help in digesting foreign materials and worn out cells. During disturbances in cellular metabolism, lysosomes burst and their enzymes are released into the cytoplasm and they digest their own cell so they are also called as “Suicidal Bags” Peroxisomes Peroxisomes are ovoid or granular structures, limited by a single membrane Peroxisomes carry out photorespiration. In animal cells they carry out lipid metabolism. They contain important enzymes as oxidases, peroxidases and catalases (which break down toxic peroxides to water and oxygen). Glyoxysomes They are single membrane bound organelles They are found in plant cells, particularly, in germinating fatty seeds e.g. Ricinus (castor) and groundnut. Fat is being converted into carbohydrates by a process called glyoxylate cycle. Glyoxysomes contain important enzymes, isocitrate, lyase, maltase Difference between Plant and Animal cell Plant cell Animal cell Cell wall present Absent Plastids present Absent Vacuoles large Small, Numerous & absent Centrioles absent Present Position of nucleus periphery Centre Autotrophic nutrition Heterotrophic nutrition Stem cells and their applications  Undifferentiated cells that can be converted into other cell types and can divide to form similar cells There are many different types of stem cells that come from different places in the body or are formed at different times in our lives. These include Embryonic stem cells (ESCs) - Cells of the inner cell mass of a blastocyst on early stage of embryo Adult stem cells also called somatic stem cells and are present in different tissues of our bodies throughout life.  Induced pluripotent stem cells are not found in the body but engineered in laboratory from cells of the body, such as those from the skin. The cells have properties similar to those of embryonic stem cells. Property of stem cell to differentiate into different cell types is called Potency Totipotent stem cells- Single cell can be converted into any cell type. Ex. Embryo cell In humans, the 2 cell staged zygote is totipotent. Pluripotent stem cells – Single cell can be converted into many cell type (all cell type) Ex: Inner cell mass of blastocyst Multipotent stem cells – These cells can be develop into more than one cell type Oligopotency – Single cell can be converted into few cell types Ex: Lymphoid stem cell Applications Whole organ manufacture Injecting cells into sight of degeneration Ex: Alzimer/Parkinson (Nerve degenerative cell) Personalised medicines – future medicines Regenerative medicine (growing tissues & organs in laboratory) Organ transplantations