Chapter 4 Bio _sz

STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

 

CHAPTER 4  CELL THEORY  Theory: Cell Theory: 

It is a statement which has an experiment proof. It is the theory, that all the organisms (whether plants or animals) are made up of cells.

Formulation:  The cell theory was collectively proposed by three different scientists namely. 1. A German botanist (Theodore) Schleiden (1838) 2. A German zoologist (M.J) Schawan (1839) and 3. A German biologist (Rudolph) Virchow (1855) Postulates:  The fundamental points of the cell theory are: 1. All organisms are composed of 1 or more cells. The cell is the unit of structure and function of living organisms. 2. The cells are formed denova (all by itself) but later proved (Virchow) that cells arise from preexisting cells. 3. The cells contain heredity material (DNA). HISTORY OF CELLS  INVENTION OF MICROSCOPE:  The microscope was invented by Italian Astronomer Galileo (1610) and improved by Dutch (Anton Van) Leeuwenhoek (1677). CELL DISCOVERY:  The cell was discovered by Robert Hooke (1665) in cork. NUCLEUS DISCOVERY:  The nucleus was discovered by Robert Brown (1831) in cells of orchid. GOLGI BODIES: Italian neurologist Camillo Golgi (1898) RIBOSOME: G.E Palade LYSOSOME: De-Duce (1949) CELL MEMBRANE:  (i) Danielli and Dawson model (1930) (ii) Singer and Nicholson model (1970) MICROSCOPES  Microscope is an (optical) instrument to see micro-organism, which can not be seen by (naked) eye. KIND OF MICROSCOPE:  Various types of microscopes are now in common use. On the basis of “light source” there are three types: 1. Light Microscope (light as source to view) 2. X-ray Microscope (X-rays as source to view) 3. Electron Microscope (Electron beam as source to view) 1. LIGHT MICROSCOPE:  Simple convex lens and stage (to view object) is used in it. It may be 1. Simple or dissecting microscope: Having single lens. 2. Compound Microscope: Having two lenses. Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

    HISTORY  1. Its history is very old from 8th century B.C 2. Simple microscopes were invented in 13th century (with spectacles) 3. Jensen and Hans (of Holland) 1590-1610 designed compound microscope. 4. Robert Hooke (1635-1703) improved magnification from 9 to (14 to) 42 times. 2. X‐RAYS MICROSCOPE:  1. Very effective for 3D view of macro molecules of cell. 2. Using electromagnetic lenses (or reflecting mirrors) to focus X-ray beam. 3. ELECTRON MICROSCOPE (EM)  Designed by Knoll and Rusk (Germany, 1932), Marten (Belgium), Perbus and Miller (Canada) from 1932-1934. There are two types of it: 1. TEM (Transmission) electron beam scan surface of specimens (image on fluorescent screen) 2. SEM (scanning) electron beam scan surface of specimens (image on TV screen) TRANSMISSION (ELECTRON MICROSCOPES)  This is a type of electron microscope which: 1. Electron Beam: is emits by metal filament or cathode. 2. Transmission: the electron beam is passes from specimen and magnetic lenses 3. Image: is seen on fluorescent screen or photographic film. SCANNING EM.  It is a type of electron microscope (EM), in which 1. Electron Beam: A very fine beam. (is used) 2. Scanning: The electron beam scans (the surface of) specimen. 3. Detector: (The metal gives off secondary electrons) the electrons are collected by detector. 4. Image: The image is seen on television screen. RESOLUTION VS MAGNIFICATION  The choice of microscope depends upon its magnification, resolution and contrast. 1) Magnification: is increase in (apparent) size of an object. 2) Resolution: is capacity to separate two (adjacent) objects. LIGHT MICROSCOPE:  1) Magnification: 10,000 x (of unaided eye).(not enough for small object) 2) Calculation: The magnification of microscope is calculated as (Magnification = Power of eyepiece x Power of objective) 3) Contrast: by staining a material (resolving power 500 times better) ELECTRON MICROSCOPE:  1) Shorter wavelength: Of electron beam. 2) Magnification: Up to 50000 x times (of un-aided eye). 3) Power: 10,000 times (of un-aided eye) Therefore, electron microscope is better for sub-cellular structures.   ISOLATION TECHNIQUES (FOR CELL COMPONENTS)  For the analysis cell components are separated from cells using various methods which involves. 1. Fractionation: To break open large size parts in ice cold environment in homogenizer 2. Centrifugation: (Spin action): large particles (like nuclei) are settle down a. As sediments and smaller parts float b. As supernatant The centrifugation of at little higher speed separates smallest particles. These fractions are then analyzed biochemically (if needed) Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  PLASMA MEMBRANE  Each cell is covered by an asymmetrical, living, porous, semi permeable sheet or layer (acts as boundary separating cytoplasm from exterior) called plasma membrane or plasma-lemma. 1. NATURE:  It is a living part of a cell (protoplasm) 2. THICKNESS:  Its thickness is 08nm (80Ao) [nanometer = 10-6mm] 3. COMPOSITION:  The cell membrane is composed by lip-protein i.e. lipid and protein 4. STRUCTURE (FLUID MOSAIC MODEL):  Fluid Mosaic, bilayer model was suggested by Singer and Nicolson according to which the plasma membrane consist of 1. Bi-layer of lipid (in which a verity of) 2. Proteins float (in fluid matrix of lipid)like ice-bergs (in sea) COMPOSITION OF LIPIDS  The lipids of plasma membrane are i. Phospholipids ii. Glycolipids iii. Sterol and iv. Cholesterol (50% lipid in animal cells and absent in plants and bacteria cells) ARRANGEMENT OF LIPIDS:  The phospholipids present in plasma membrane consist of (i) Head and (ii) Tail 1) Hydrophobic end (non-polar/tail end of FA and glycerol) presents toward centre. 2) Hydrophilic end (polar / head end of IFA and phosphate) present towards surface. The nonpolar end face each other (between every two phospholipids lies cholesterol) FUNCTION OF LIPID:  1. Lipids lower surface tension. 2. The lipid gives rigidity to cell membrane. COMPOSITION OF PROTEINS:  The protein in cell membrane is a. Glycoprotein b. Globular protein c. Proteoglycal ARRANGEMENT OF PROTEINS:  The protein present in lipid bilayer is divided into two groups. 1. Intrinsic (Integral) protein: penetrates lipids bilayer partially or wholly. 2. Extrinsic (Peripheral) protein: present entirely outside (float like iceberg) lipid. FUNCTION OF PROTEIN:  1. Intrinsic protein form channel for water soluble (ions) molecules. 2. Acts as carrier for active transport (extrinsic) 3. Some acts as enzymes 4. Regulates in pores   FUNCTION OF CELL MEMBRANE:  It performs the two main functions: 1. The protection of protoplasm 2. The regulation of materials (in and out of cell) through its permeability

Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  PERMEABILITY OF MEMBRANE:  The permeability of the plasma membrane is regulated by Five processes Osmosis, Diffusion, Active transport, (Phagocytosis and Pinocytes) Endo and Exocy DIFFUSION (PASSIVE TRANSPORT):  It is the spreading or free movement of molecules (or aims) from the region of higher concentration to the region of lower concentration (till equilibrium condition) SIGNIFICANCE:  Oxygen and digested food (glucose, amino acids, and fatty acids) into the cell by diffusion, while excretory waste diffuse out (into surrounding fluid) by it. OSMOSIS:  It is the process of diffusion of water by semi permeable membrane or the movement of solvent molecules from higher to low concentration across semi-permeable membrane (cell membrane itself acts as semi permeable membrane). SIGNIFICANCE:  a) The liquids, primarily water, enter and leave the cell by osmosis. b) It helps to maintain a balance (osmotic pressure) in and out of cell. ACTIVE TRANSPORT:  It is the movement of molecules, against the concentration, by the expenditure of energy through a carrier. (i.e. the movement of molecules from the region of lower conc. To higher conc. by protein using ATP as energy) SIGNIFICANCES:  The absorption of excess food (amino acids, glucose), ions (K+ ions and the pumping out of Na+ ion) takes place by active transport. CONDITIONS:  1) It is unidirectional 2) ATP supplies energy and 3) Protein acts as carrier 4) Endocytosis (taking in material by infolding) PHAGOCYTOTIS (CELL ENGULFING OR EATING)  1. It is the process of picking and ingesting of large solid particles by plasma membrane (which can not enter by diffusion, osmosis or active transport). 2. It is endocytosis of large solid particles by cell membrane. SIGNIFICANCE:  1. The cell ingests food particles by Phagocytosis. 2. The WBC picks foreign particles (like certain bacteria) by it. STEPS OF PHAGO/PINOCYTOSIS  1. Plasma membrane invaginate to form vacuole (which pinches of) 2. The enzymes form Lysosome (make it soluble) digest it. 3. The soluble products are absorbed (By cytoplasm) and vacuole moves to surface to release indigestible material (out of cell) by exocytose PINOCYTOSIS (CELL DRINKING)  1. It is the process of fluid intake, for absorbing fluid by forming pino or cytic vesicle. (The fluid which cannot be absorbed by osmosis enters through it) 2. It is a type of endocytosis of fluid material in bulk. It is supplementary process for all absorption into cytoplasm. ADVANTAGES:  Pinocytosis helps in the absorption of hormones, lipids etc i.e. 1) Hormones to its receptor (Golgi bodies) 2) Lipids to its receptor (Lysosome which contains lipase enzyme to digest lipids) Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  TYPES OF CELLS (EU & PRO‐KARYOTES)  On the basis of presence and absence of true nucleus (and organelles) are two types of cells Eukaryotes & Prokaryotes. EUKARYOTES (EU = TRUE, KARYON = NUCLEUS)  1. Eukaryotic cells bears true nucleus (nucleus with nuclear membrane) 2. Bears membrane bound organelles (mitochondria, plastids, Golgi appall) 3. May be unicellular (amoeba, chlorella) or Multicellular (Hydra, starfish) PROKARYOTES (PRO = PRIMITIVE, KARYON = NUCLEUS)  1. True nucleus (membrane nucleus) is absent. 2. Nuclear material is coiled and conc.: is nucleoid (central region) 3. Membrane bound organelles (mitochondria, plastids) are absent 4. All unicellular (bacteria, cynobacteria) 5. Contains mesosomse (infold of plasma membrane for respiration, photosynthesis, nitrogen fixation etc.) CYTOPLASM  The protoplasm outside nucleus (i.e. between cell membrane and nucleus) is called cytoplasm. 1. Nature: Cytoplasm is semi-fluid colloid (jelly like) 2. Cyclosis: is the streaming or circular movement of cytoplasm. 3. Parts: Cytoplasm has two main parts (as in Amoeba and most cells) i. Ectoplasm: outer, clear ii. Endoplasm: inner, granular 4. Cytosol: (cell solution) fluid matrix of cell (in which organelles present) 5. Cytosol 6. Composition: It is watery solution of salts, sugar, amino acids, protein, fatty acids, nucleotides etc. 7. Cytoskeleton: a network of protein fibers present in Cytosol (giving rigidity to cell & helps in movement in unicellular) CYTOPLASMIC ORGANELLES  The organelles are divided into two groups’ i.e. 1) Membrane bound organelles: (i) ER (ii) Mitochondria (iii) Golgi apparatus (iv) Lysosomes (v) Plastids and micro-bodies (i.e. Peroxi-somes and Gly.oxy.somes) 2) Non-membrane bound organelles: (i) Ribosome (ii) Centriole (iii) Vacuole CELL ORGANELLES  1. ENDOPLASMIC RETICULUM (ER)  It is the network of tubes in the cytoplasm of Eukaryotic cells from cell membrane to nuclear membrane discovered by Keith Porter (1940) 1. Shape: ER is tubular in structure, consist of sac called cisternae. 2. Size: The tubes are branched with the thickness of 04nm consist of Lip-Protein. 3. Types: ER are two types 1) Smooth or A-granular ER without ribosomes. 2) Rough or Granular ER with spherical ribosomes on outer surface.

Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  I. SMOOTH ER (SER)  It is the type of ER which is without ribosomes present in steroid forming cells like 1. Adipose cells 2. Interstitial cells 3. Glycogen storming cells 4. Muscle cells FUNCTIONS:  1. Transporting materials in and out of cells e.g. RNA from nucleus to organelles in cytoplasm. 2. Provide structure frame work, it also helps in detoxification of harmful drugs. (as in liver cells) 3. It is undivided in lipid synthesis. The sterol, cholesterol etc. II. ROUGH ER (RER)  It is the type of ER bearing ribosomes on outer membrane present in synthesizing cells like 1. Slivery Glands 2. Pancreas FUNCTIONS:  1. It is the platform for ribosomes. (ribosomes form protein) 2. It is responsible for forming conjugate by combining protein and lipid like lip-protein, Glycolipid, Phospholipid etc. 3. It increases surface area for metabolic activities. 4. It regenerates cell membrane. III. MITOCHONDRIA (OR CHONDRIOSOMES)  These are filamentous bodies in the cytoplasm of Eukaryotes for the supply of energy. SHAPE:  Each mitochondrion is filamentous, rod (let) like or fibrous. SIZE:  Each mitochondrion is 10nm long and 0.1-0.2nm in diameter (first observed by Kolliker) about 1000 in each cell. STRUCTURE:  Each mitochondria is covered by a double, thin, lip-protein membrane (i) Outer, smooth membrane (ii) Inner, folded membrane partition with called cristae. (iii) Filled with fluid called Matrix. FUNCTION:  1. It supplies energy to the cell that’s why called “Power house” of cell. 2. Oxidation of food (Glucose, Amino acids, fatty acids) takes place (to form CO2 & water) i.e. for aerobic respiration. 3. The energy rich compound (ATP, adenosine triphosphate) are stored in mitochondria. IV. GOLGI APPARATUS/ BODIES (OR DICTYOSOME)  Golgi bodies/Complex is a stock of flattened bodies in the cytoplasm for the secretion. DISCOVERY:  First observed by Italian Scientist Camillo Golgi (1898) SHAPE:  Cluster of flattened, parallel sacs like. SIZE:  It is about 1-3mμ long and mμ wide present one on each. STRUCTURE:  Consist of sacs called (i) Cisternae with small (ii) Vesicles at tips (golgian vacuoles) FUNCTION:  1. Golgi bodies help in secretion (hormones, enzymes) that’s why present in glandular cells. 2. Contain secretary granular for synthesis of i. Proteins Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  ii. Enzymes iii. Other Substances 3. Forms Lysosomes 4. Forms materials (cellulose) for the synthesis of cell wall in plants. V. CENTROSOMES  It is an oval body, close to nucleus in animal cell. Flower plants consist of two rod. Like centrioles for help in cell division. SHAPE:  It is oval body consist of two grains (centrioles) STRUCTURE:  Each consists of two rod-like centrioles. Each centrioles is cylindrical 0.5nm long and 0.2nm in diameter composed of triplet of nine, parallel hollow, micro-tubules (containing a protein Tubulin and RNA) FUNCTION:  Centrioles help in cell division (in migration of chromosomes). During cell division each centriole move to opposite pole and forms spindle of fibers called astral rays. (Because of two asters the division is Amphiastral).   VI. LYSOSOMES: (DIGESTORS )  These are spherical bodies in the cytoplasm of animal cells for digestion of food by digestive enzymes during Phagocytosis discovered by De-Duce (1949) SHAPE:  These are little sac-like roughly rounded bodies, few microns in size. STRUCTURE:  These are surrounded by single membrane filled with enzymes. FUNCTION:  1. Digestive Enzymes: These contain enzymes for digestion of food material. 2. Destroyers: i) These digest foreign particles + bacteria in WBC (Leukocytes) ii) These also destroy worn out cells organelles. 3. Suicidal sacs: These destroy whole cell (Autolysis or self killing when ruptured) 4. Endocytosis: Helps in phago & Pinocytosis with vacuoles forming secondary lysosomes VII. VACUOLES: (CELL BUBBLES/CAVITY)  These are non-protoplasmic spherical membrane free filmy bodies containing clear liquid SHAPE:  These are bubble like, spherical bodies. In animal cell small and in plant large. STRUCTURE:  These are without membrane (except in plant cells) bears film like structure with tonoplast. FUNCTION:  1. STORAGE:   The vacuole stores glucose, water or waste. (mostly water and sometimes protein, sugar and minerals) 2. SECONDARY LYSOSOMES:  Vacuoles help in Phagocytosis and Pinocytosis in animal cells by combining with lysosomes (in plant cell vacuole acts as lysosomes) 3. CELL SAP:  The salt solution called cell sap in plants is stored in it (sap gives turns) 4. OSMOREGULATION:   In protists contractile vacuole removes extra water from cell. 5. DIGESTER:  In Protists food vacuole help in digestion containing ribonucleas

Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  PLASTIDS (COLORING BODIES)  Plastids are disc-like, coloring, storing or photosynthetic organelles found in cytoplasm of plant cells only. (And protists like Euglena) formed by colorless proplastids. TYPES:  These are of three types: i) Chloroplasts ii) Chromoplasts iii) Leucoplasts 1.

CHLOROPLASTS (Chloro=green, Plast=living) Chloroplasts are green plastids containing green color chlorophyll. 1. SHAPE:  These are disk like plastids. 2. SIZE:  About 5 microns in diameter. 3. STRUCTURE:  Covered by double membranes with chlorophyll (green pigment) and nucleic acid. I.e. RNA (protein synthesis) and DNA for self replication. 4. FUNCTION:  Photosynthetic forming food in sunlight by forming ATP. 5.  CONVERSION:  May convert to chromoplast as in Mango. Leukoplast of potato may become chloroplast on exposure to light. 2. LEUCOPLAST (Leuco = white) These are colorless plastids with out pigment. Present in root seeds young and underground parts of plants. It converts and store starch from glucose and store oil in seeds. 3. CHROMOPLAST (Chromo = color) A type of colored plastids which gave color to fruits and flowers and other colored parts. Contain pigments like Xanthophylls(Yellow), Carotene(Orange), Anthrocyanin(Blue)pigments MICROTUBULES  These are fibrous, microscopic tubules of protein for cytoskeleton (microfibric) discovered by Ledbetter and Forter (1963). SIZE:  These are several micron (16-100µ) long and 25nm in diameter. COMPOSITION:   These are composed of protein called Tubulin (may be singly or in bundles) OCCURRENCE:  Present in Pseudopodia (Axopods), Cilia, Flagella and Centriole FUNCTIONS:  These help in 1. Cytoskeleton 2. Movement of body in Cilia and Flagella 3. Movement of Chromosomes in Centriole for Chromosomes migration. 4. Cellulose deposition RIBOSOMES  These are rounded bodies, present in free and attached state in the cytoplasm of most cells for proteins synthesis (formed by nucleolus) SIZE:  These are smallest organelles. 20nm in diameter. SHAPE:  These are tiny; spherical bodies about one million per cell. TYPES:  The ribosomes are of three types: Efforts By: Miss Amber  8  

STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  (i) (ii) (iii)

Free: Attached: Poly-ribosomes:

Present spread in Cytoplasm. Attached with endoplasmic reticulum (RER) Are the chain of ribosomes.

STRUCTURE:   Each ribosome consists of two sub units. (1) Large 60-S (2) Small 40-S. These unequal units attached to form 80-S particle. The two a) The layer; dome-shaped (60-S) subunit forms enzymes (for the linkage of amino acids) b) The smaller, cap like (40-S) subunit is for attachment to ER. FRACTION:  These form protein and considered as protein factories of a cell. TYPES OF CELLS  The cells are of two types on the basis of presence or absence of Nucleus 1. Prokaryotic 2. Eukaryotic 1)

PROKARYOTIC CELLS: (VIRUS, BACTERIA, BESTOC)  i. The Nuclear material is without nuclear membrane ii. The membrane bound organelles (Mitochondria, ER, Golgi-bodies, Lysosomes, Chloroplast and Nucleus)

2) EUKARYOTIC CELLS: (ALGAE, FUNGI, PROTOZOAN, PLANT, ANIMAL CELLS)  i. The nucleus with distinct nuclear membrane is present ii. The membrane bound organelles are present: These differ in following respects: Eukaryotic 1. 2. 3. 4. 5. 6. 7.

Size Cell wall Membrane bound organelles Ribosomes Lysosomes Nucleus Centriole

8. Vacuole 9. Cilia / Flagella (with 9 + 2 fibril) 10. Golgi Bodies

PLANT CELL 10-60µ Present Present Present (80-S) Absent Present Absent in higher Plants Large Vacuole Absent in Higher Plants Several Present

Prokaryotic

ANIMAL CELL 50-100µ Absent Present Present (80-S) Present Present Present Absent in Protists Small Vacuoles Present

BACTERIA 2-5µ Present Absent Present Absent Absent Absent No Vacuole Absent

Only 1/cell

Absent

TYPES OF LEUKOPLASTS  i. Amylo-plasts: Stores starch e.g. Potato ii. Lipo-plasts: Stores oil e.g. Sunflowers seeds iii. Proto-plasts: Stores proteins e.g. Beans seeds. CELL‐WALL  The cell wall is a non-living, dead wall of cellulose, present outside cell membrane in plant cells. NATURE:  Cell wall is dead (formed by protoplasm), permeable layer. FORMATION:  Cell wall is formed by Golgi apparatus of plant cells. Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  COMPOSITION:  Cell wall is mainly composed of Cellulose (a polysaccharide of 2 to 3 thousand glucose) ARRANGEMENT:  The cellulose fibers in a cell wall is composed of network of fibers arranged in layers (criss-cross arrangement) LAYERS OF CELL WALL:  The cell wall consist of three layers 1) Middle lamella (formed first) 2) Primary cell wall (outer earlier) 3) Secondary cell wall (inner most, formed in last) 1. Middle Lamella: 1) It is formed during cell division (as cell plate) or cementing layers (between daughter cells) 2) It is composed of a) Calcium pectate b) Magnesium pectate 2. Primary Cell-Wall: 1) It is outer most layer. (Hemi-cellulose as matrix and cellulose fiber) 2) Consist of hemi cellular (50%), cellulose (25%) and pectin. 3. Secondary Wall: 1) It is formed inside primary wall (during maturation, when the cell growth ceases) 2) consist of cellulose and lignin. PLASMODESMATA (CONNECTION)  The Plasmodesmata are the places where. 1. No deposition of cellulose 2. Cellular consist of neighboring cells connects. FUNCTIONS (CELL WALL):  The cell wall performs following functions: 1) Shape: It gives shape to cell. 2) Supports: It gives mechanical support. 3) Skeletal frame: It gives frame work of cell. 4) Permeability: The Hydrophilic nature helps in imbiding water i.e. movement of both water and solutes. LYSOSOMAL STORAGE DISEASES:  W.G Hers, 1965 (Belgium) found that 1) α-glycosidase (lysosomal enzymes absences) 2) Swelling of Lysosome (due to glycogen) or storage disease. 3) Causing damage to cell DISORDERS:  The deficiency of lysosomal enzymes causes 30 disorders like sphingo lipid (storage disease) including. i) Tay.sach’s disease: (mental retardation, death age 3, blindness) ii) Gaucher’s disease: (mental retardation, death age 2, Liver and spleen enlargement, loss long bones) iii) Krabbe’s disease: (mental retardation , death age 2, Loss of myelin) Sphingosine (an unsaturated amino alcohol) + lipid = sphingo. Lipid in myelin. INTERMEDIATE FILAMENTS (CYTOSKELETON)  The supporting (cytoskeleton) protein (fibrous protein) intermediate between (8-11 nm) micro tubules and microfilaments. SIZE:  8-11nm is diameter. STRUCTURE:  Rope like polymer of fibrous protein (like Keratin) Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  FUNCTION:  1. Maintains shape of cell. 2. Supports (mechanical strength to) hair, nail, nuclear envelope (as do not assemble and disassemble) GLY.OXY.SOMES  Gly.oxy.somes is single membrane bounded micro bodies present in plant cells to metabolize some molecules (like Glycolate) involved in photosynthesis and respiration (through oxidation of fatty acids.) SHAPE:  These are some what rounded micro bodies. SIZE:  About 0.3-1.5 micron in diameter. STRUCTURE:  Bounded by single membrane with granular material in stroma. MODIFICATION:  These are modified Peroxi-somes to perform metabolism. OCCURRENCE:  Present in plants e.g. germinating castor oil seedling. FUNCTIONS:  1. Gluconeogensis: i.e. conversion of fat into carbohydrates or Fat metabolism 2. Photorespiration: (in green leaves) respiration in presence of light & O2. 3. Glyoxalate cycle: Glycolate is formed in chloroplast (during photorespiration) and passes out into the cytoplasm and is oxidized in Gly.oxy.somes. 4. Relationships: a close relationship is present between i. Gly.oxy.somes and chloroplast ii. Gly.oxy.somes and mitochondria MICRO‐FILAMENTS  Microfilaments are delicate, cytoplasmic, protein (globular, helical) thread like micro bodies present in cells for movement. SHAPE & SIZE:  These are solids, helical (or interwine), actin (protein) threads of 7nm diameter. OCCURRENCE:  Present abundantly during cell cleavage (cell division), amoeboid cells pseudopodia muscles (single standard polymers of small globular proteins subunits) FUNCTION:  Help in i. Support ii. Movement (in pseudopodia) iii. Movement (in actin of muscles) DIFFERENCE BETWEEN MICROTUBULES AND  MICROFILAMENTS  Although, both are for cytoskeleton, but in some respects. CHARACTERISTICS 1. Diameter 2 Thickness 3. Nature / Shape 4. Protein (globular) 5. Number 6. Arrangement

MICROTUBULES 25nm Thick Hollow cylinder Tubulin Hundred of thousands sub-units In 13 columns (or protofilaments)

Efforts By: Miss Amber   

MICROFILAMENTS 7nm Thin Solid Actin Two chains Helical or interwine

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  FUNCTION OF CYTOSKELETON  The cytoskeleton is a network fibrous (globular) proteins thread consist of (i) microtubules (ii) micro filaments (iii) intermediate filaments which helps in (1) Cell divisions (mitosis, meiosis and cytokinesis) (2) Maintenance of cell shape. (3) Cell wall deposition (cellulose deposition) (4) In animal cells & lower plants from structure (like centriole cilia & flagella) PEROXI‐SOME  Peroxi-somes are single membrane bounded microbodies, present in plants and animals cells to metabolize and detoxify H2O2 or alcohol. SHAPE:  These are almost spherical organelles (or microbodies) SIZE:  About 0.3 to 1.5µ in diameter. STRUCTURE:  Bounded by a single unit membrane. Containing finely granular material (in some contains cores or nucleoid) FUNCTION:  1. Metabolism of H2O2 (a metabolic poison) 2. Protection from harmful metabolites 3. In Liver and Kidney these contains enzymes (cataloes) to remove NUCLEUS  It is oval or round, controlling body in all cells except prokaryotes. NOMENCLATURE:  Nucleus is derived from Latin “Nuclo” i.e Kernal or out DISCOVERY:  Discovered by Robert Brown, 1831. SHAPE:  It is usually spherical or elliptical (oval) mass of protoplasm. SIZE:  Its size is 10-20nm in diameter. NUMBER:  It may be one, two (paramecium), several (opilina)/cell or altogether absent (in prokaryotes) STRUCTURE:  1. Nuclear membrane: (Nucleo-Lemma) Each nucleus in Eukaryote is covered by double, porous membrane. 2. Nucleoplasm: (Karyolymph) The nucleus is filled by protein rich fluid called Nucleoplasm. 3. Chromatin Network: (Nuclear reticulum) A network of chromosomes composed of DNA and protein which breaks cell division forms chromosomes. The chromosome number vary in different species (8=fruitfly, 46=Humans, 20=Corn 4. Genes: (Hereditary units) The genes are tiny granules located on chromosomes. NUCLEOLUS:  One or two spherical bodies, RNA containing bodies are pressed. FUNCTION:  1) Controlling centre (acts as brain) of cell. 2) Heredity material in form of Genes transfers characters to daughter cells. 3) RNA in nucleolus helps in Protein synthesis with ribosomes. Efforts By: Miss Amber   

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STUDENTS’ ZONE (BIOLOGY XI) 

November  28, 2008

  CHROMOSOMES:  The chromosomes are stainable, thread like structures in the nucleus present in form of network called chromatin network. STRUCTURE:  Each chromosomes consist of two parts: 1. Centromere: The central, achromatic (unstain) part 2. Chromatid: The loop like part attached to Centromere. Each chromatid consist of two parts: a. Chromonema: is thread like part of chromatid. b. Chromosomes: are granules or beaded part of Chromatid (chromone) which are thickening in chromatid (also called chromosomes). TYPES:  There are four main types of chromosomes on the basis of position of centromere (Kinetochore)(i.e. its central, oval, unstain part) Meta, sub-meta, acro and telocentric 1. Meta.Centric: When the centromere is present in the middle of chromosomes. They possess almost equal arms (chromatids) and generally V-shaped. 2. Sub.Meta.Centric: When the centromere is slightly below centre (away from middle). The arms are unequal length. These chromosomes are usually L or J shaped. 3. Acro.Centric/Sub-Teld (Acro=apex or tip) When the centromere is present far away from middle (far away or above centre) forming two unequal arms i.e. one too short and other too long arm. (the centro-mere is sub-terminal) 4. Telo:Centric When centromere is present at tip (i.e. at one side and arms on other side). These appear rodlike.

Efforts By: Miss Amber   

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