Saran's Learn Microbiology

  RIBOSOMES —   Bacterial cells have thousands of Ribosomes in their cytoplasm, which gives cytoplasm a grainy appearance. —   Number of Ribosomes in bacterial cell varies from 10000 to 15000. —   Chemically, a Ribosome is a combination of a special type of RNA called ribosomal RNA, or rRNA (about 60 %), and protein (40 %). —   Ribosomes are the sites of Protein synthesis (Translation) in cells. —   The Ribosomes are held together by mRNA and form Polyribosomes or Polysomes.   —   All Ribosomes are composed of two sub-units, each of which is composed of polypeptides and molecules of RNA called ribosomal RNA (rRNA). The sub-units of Prokaryotic 70S ribosomes are a smaller 30S sub-unit and a larger 50S sub-unit. ü   The 30S sub-unit contains Polypeptides and a single rRNA molecule ü   The 50S sub-unit has Polypeptides and two rRNA molecules. —   The letter S refers to Svedberg units, which indicate the relative rate of sedimentation during ultra-high-speed centrifugatio

  CELL INCLUSIONS —       Within the cytoplasm of prokaryotic cells, several kinds of reserve deposits, known as Inclusions or Cell Inclusions or Inclusion bodies. ·    Cells may accumulate certain nutrients when they are plentiful and use them when the environment is deficient. ·        Some inclusions arc common to a wide variety of bacteria, whereas others are limited to a small number of species and therefore serve as a basis for identification. TYPES OF CELL INCLUSIONS a)      Metachromatic Granules b)      Polysaccharide Granules c)      Lipid Inclusions d)      Sulfur Granules e)      Carboxysomes a) Metachromatic granules ·    Metachromatic granules are large inclusions that take their name from the fact that they sometimes stain red with certain blue dyes such as Methylene blue (Metachromasia). ·     Metachromatic Granules are made up of Polymetaphosphates and also called as Volutins or Volutin Granules or Babe Ernst Granules or Polar Bodies. ·     Vo

  PLASMA MEMBRANE —   Plasma membrane is also called as Cytoplasmic Membrane or Cell Membrane. —   It act as a boundary of the bacterial cell. —   Plasma membrane is found in the bacterial cells that separates the interior of the cell from the outside environment. —   Plasma membrane measures about 5 to 10 nm thick. —   In Prokaryotes, the Plasma membrane is made up of Phospholipids (20 % to 30 %) and Proteins (60 % to 70 %). In Eukaryotes, the Plasma membrane is made up of Carbohydrates and Streols (Cholesterol). —   Generally, Plasma membrane is a Phospholipid bilayer and Semipermeable.   —   The Phospholipid structure is Amphipathic (a molecule, especially Protein, having both Hydrophilic and Hydrophobic parts) in nature and measures approximately 8 nm thick. —   The Phospholipid structure has Hydrophilic (water loving) heads and Hydrophobic (water hating) tails.   Structure of Phospholipid FLUID-MOSAIC MODEL STRUCTURE OF PLASMA MEMBRANE —   The dynamic arrangem

Difference between Gram positive bacterial cell wall and Gram negative bacterial cell wall Features Gram Positive Bacterial Cell wall Gram Negative Bacterial Cell wall Gram staining Appears in Violet colour Appears in Pink colour Thickness 15 – 18 nm 7 – 8 nm Peptidoglycan Thick (Multilayered) Thin (Single layered) Teichoic acids Present Absent Periplasmic space Absent Present Outer membrane Absent Present Lipopolysaccharides Low High Lipid & Lipoproteins Low (Only in Acid fast bacteria have lipid linked to Peptidoglycan) High (because of the presence of Outer membrane) Porins Absent Present Cell wall disruption by Lysozymes High