Lesson 2

• Cell


  The structural and functional unit of an organism, the smallest structure capable of performing all the functions necessary for life
• Cell Biology


  The classical branch of biology that deals with the study of structure, function and life of a cell
• Robert Hooke


  • In 1665, an English scientist who observed honeycomb like dead cells in a thin slice of cork under microscope, coined the term "cellulae" (Latin, "small rooms")
• Anton van Leeuwenhoek


  • A Dutch scientist recognized for making some of the earliest microscopes and observing things that no one had seen before
• Matthias Schleiden


  • In 1838, a botanist made a careful study of plant tissues and developed the first statement "are aggregates of fully individualized, independent, separate beings, namely the cells themselves"
• Theodor Schwann


  • In 1839, a British zoologist based on his studies on different animal cells formulated "cell theory"
• Modern Cell Theory


  • The cell is the smallest living unit in all organisms
  • All living things are made of cells
  • All cells come from other pre-existing cells
• A typical cell has an outer non living layer called cell wall, a cell membrane that encloses protoplasm, which has a semi fluid matrix called cytoplasm and a large membrane bound structure called Nucleus
• The cytoplasm has many membrane bound structures like endoplasmic reticulum, golgibodies, mitochondria, plastids, micro bodies, vacuoles; and non membranous structures like Centrosome and ribosomes. These are called cell organelles
• Differences between plant and animal cells

  • Plant cell has cell wall, lacks centrioles, has plastids, has large vacuole
  • Animal cell lacks cell wall, has centrioles, lacks plastids, may have small vacuoles
• Protoplast


  Includes cell membrane and protoplasm
• Cell Membrane/Plasma Membrane


  A semi permeable membrane composed of phospholipids, proteins, carbohydrates and cholesterol, allows the outward and inward movement of molecules across it
• Protoplasm


  The living substance of the cell that possesses all vital products made up of inorganic and organic molecules, includes cytoplasm and nucleus
• Cytoplasm


  The jellylike, semi fluid matrix present between the cell membrane and nuclear membrane, has various living cell inclusions called cell organelles and non living cell inclusions called ergastic substances and cytoskeletal elements
• Endoplasmic Reticulum (ER)


  • A network of membrane bound tubular structures in the cytoplasm, extends from cell membrane to nuclear membrane, exists as flattened sacs called cisternae, unbranched tubules and oval vesicles, has two types: Rough ER with 80s ribosomes on its surface, and Smooth ER without ribosomes
• Golgi Bodies/Golgi Complex/Golgi Apparatus/Dictyosomes


  • A group of curved, flattened plate like compartments called cisternae stacked one above the other, produce a network of tubules from the periphery that end in spherical enzyme filled vesicles, also called "Packaging centres" of the cell
• Mitochondria/Chondriosome


  • A spherical or rod shaped cell organelle with two membranes, the outer membrane is smooth and the inner membrane produces finger like infoldings called cristae, the inner membrane has stalked particles called ATP synthase complex, the mitochondrial cavity is filled with a homogenous granular mitochondrial matrix that has circular mitochondrial DNA, RNA, 70s ribosomes, proteins, enzymes and lipids, also called "Power houses of the cell"
• Plastids


  • Present in plant cells and euglenoids, classified into chromoplasts (contain carotenoids), leucoplasts (store food materials), and chloroplasts (contain chlorophylls and carotenoids, have photosynthetic pigments and complexes), also called "Kitchen of the cell"
• Vacuoles


  • Single membrane bound sac like vesicles present in cytoplasm, plant cells have large vacuole and animal cells may have smaller vacuoles, filled with a watery fluid called cell sap, different types include contractile, food, gas, and storage vacuoles
• Microbodies


  • Small, spherical, single membrane bound structures present in cytoplasm, include lysosomes (filled with hydrolytic enzymes), peroxysomes (oxidize substrates), and glyoxysomes (store fat and convert it into carbohydrates)
• Ribosomes


  • Granular, nonmembranous sub spherical structures present in the cytoplasm, mitochondria and chloroplast, also found attached to Rough ER and nuclear membrane, composed of r-RNA and proteins, prokaryotes have 70s and eukaryotes have 80s ribosomes in cytoplasm, also called "Protein factories of the cell"
• Centrosome


  • Found in animal cells and some motile algae, absent in plant cells, present near the nucleus, has two cylindrical structures called centrioles
• Mitochondria and plastids have their own DNA called organelle DNA and 70s ribosomes, so they are able to prepare their own proteins, hence they are considered as 'semiautonomous cell organelles'
• S.J.Singer and G. Nicolson (1974) proposed Fluid Mosaic model to describe the structure of plasma membrane
• Glyoxysomes


  Store fat and convert it into carbohydrates
• NON MEMBRANOUS CELL ORGANELLES PRESENT IN THE CYTOPLASM
• Ribosomes


  Granular, nonmembranous sub spherical structures present in the cytoplasm, mitochondria and chloroplast. They are also found attached to Rough ER and nuclear membrane. Composed of r-RNA and proteins. Prokaryotes have 70s (50s + 30s) ribosomes in cytoplasm. Eukaryotes have 80s (60s+40s) ribosomes in cytoplasm and 70s (50s+30s) ribosomes in mitochondria and plastids. Common name: Protein factories of the cell. Function: Sites of polypeptide or protein synthesis
• Centrosome


  Found in animal cells and some motile algae, absent in plant cells. Present near the nucleus. Has two cylindrical structures called centrioles surrounded by a less denser cytosol called centrosphere. Each centriole is made up of a whorl of nine triplets of microtubules.
• Centrosome


  • They form asters and organize the formation of spindle fibres during cell division
  • They are involved in the formation of cilia, flagella and axial filament in sperms
• Ergastic substances


  • Reserve food materials (starch, protein, oils)
  • Secretory products (nectar, pigments, enzymes)
  • Excretory products (alkaloids, resins, latex, tannins)
  • Mineral crystals (cystoliths, raphides, druses)
• Cystoliths


  Grape like cluster of calcium carbonate crystals
• Raphides


  Needle or rod like crystals of calcium oxalate. Cells containing raphides are called Idioblasts
• Druses (Sphaeroraphides)


  Spherical bodies containing calcium oxalate crystals
• Secondary Metabolites


  Organic compounds not directly involved in normal growth, development, or reproduction of an organism, unlike primary metabolites. Includes alkaloids, rubber, antibiotics, drugs, coloured pigments, scents, gums & spices
• Cytoskeleton


  Complex network of interconnected microfilaments and microtubules of protein fibres present in cytoplasm. Helps in mechanical support, cell motility, cell division and maintenance of the shape of the cell
• NUCLEUS (Karyon)
• Nucleus


  Darkly stainable, largest cell organelle present in eukaryotic cells. Usually spherical, may be lobed or kidney shaped. Has an outer double layered nuclear membrane with nuclear pores, a transparent granular matrix called nucleoplasm or karyolymph, chromatin network composed of DNA and histones and a darkly stainable spherical body called Nucleolus.
• Types of cells based on presence of nucleus

  • Nucleated or Eunucleated cells
  • Enucleated cells (Mammalian RBC, Sieve tube members of angiosperms)
  • Prokaryotic cells (Bacteria, Nostoc)
  • Eukaryotic cells (Higher plant & animal cell)
• Nucleolus


  Ribosome factory, involved in the synthesis of necessary molecules required for the production of ribosomes
• Prokaryotic cell


  Cell having incipient or primitive nucleus, without nuclear membrane. Has only DNA but not histones unlike eukaryotic cell.