Microbiology lecture

• Cells


  All living beings are cellular, bounded by a plasma membrane which is made of special phospholipids and is studded with many complex protein pores, channels, gates, receptors, recognition proteins, and contain cytoplasm which contains water, and many chemicals and special structures, as well as the genome
• Lipid bilayer


  • Studded with very large numbers and many types of proteins such as transport proteins, receptor or recognition proteins, with a high capacity for these protein molecules to move around in the cell membrane, as can the actual lipid molecules of the membrane
• Fluid mosaic model


  Model describing the structure of the cell membrane
• Prokaryotic cells


  • Do NOT have a discrete membrane bound nucleus that contains chromosomes, have a none membrane bound single circular DNA chromosome, the region where their circular DNA macromolecule exists is called the nucleoid, bacterial DNA is not associated with special cationic proteins called histones
• Eukaryotic cells


  • DO have a membrane bound genome consisting of more than one LINEAR chromosome, bounded by a double layered nuclear membrane, Fungal, protist, plant and animal cells are eukaryotic
• Cell wall of prokaryotes

  • Rigid cell wall that determines the shape of the cell, and in most cases the wall contains peptidoglycan, a unique and complex acidic polysaccharide that lends rigidity to the wall and serves to resist the very high internal osmotic pressure that would burst (lyse) the cell unless the wall was present, metabolically inert, it does not participate actively in transport processes in and out of cells
• Penicillins


  Kill bacteria by interfering with the synthesis of peptidoglycan in cell walls
• Mycoplasma


  • Do not have cell walls
• Archaebacteria


  • Do have cell walls, but peptidoglycan is not a part of their cell wall structure
• Gram stain


  Refers to a dye staining procedure involving sequential treatment of bacteria on a slide with crystal violet dye, iodine, alcohol and safranin dye, one of two results, the dyed cell is red when viewed under the microscope and is termed as Gram negative, or purple when viewed under the microscope and is termed as Gram positive, the Gram result is correlated with a particular cell wall structure, and it is the iodine treatment step that distinguishes between Gram positive and Gram negative, alcohol is the point where Gram positive and Gram negative are differentiated
• Gram positive bacteria


  • Have thick walls with a dense homogeneous layer of peptidoglycan
• Gram negative bacteria


  • Have thin cell walls with much less peptidoglycan and an EXTRA outer lipid membrane (not a cell membrane) that contains a toxic compound called lipopolysaccharide (LPS)
• Prokaryotic ribosomes


  • Non-membrane bound organelles that synthesize proteins, but those of the prokaryotes are smaller, complex macro (very large) molecules composed of a smaller and a larger subunit, consist of a special nucleic acid (ribosomal nucleic acid) and protein and their function is to synthesize proteins by reading the mRNA copy of sections of DNA, 80S in eukaryotic cells and 70S in bacteria and mitochondria
• Membrane bound organelles


  • Serve to compartmentalize certain reactions into separated spaces in eukaryotic cells, allow such reactions to be physically isolated so that they can occur at the same time, small specialized organelles also allow reactants to be more concentrated, prokaryotes (bacteria) do not have membrane bound organelle
• Endoplasmic reticulum


  • Complex folding of flattened membrane bound spaces that provides a large surface area for reactions that occur on or across membranes, rough ER is "rough" in appearance because it is extensively "studded" on the exterior of the membrane with ribosomes that synthesize and release proteins into the volume enclosed by the ER membranes, smooth ER does not have associated ribosomes and is generally involved in producing steroids and other lipids or in reactions not involving protein synthesis
• Golgi bodies


  • Composed of a nested set of flattened vacuoles that receive proteins and other molecules from the ER and prepare, modify (by addition of sugars or phosphates etc) and transport them in MBO's called vesicles, Vesicles are small membrane bound spheres, Golgi bodies are also involved in forming lysosomes
• Other vesicles


  • Lysosomes- contain destructive digestive ozidizing enzymes
  • Peroxisomes- neutralize hydrogen peroxide
  • Endocytosis- pinch off to enclose and import materials
  • Exocytosis- export substances from the cell
• Nucleus


  • Spherical lipid double membrane enclosing the chromosomes, contains many pores, within it are the linear chromosomes, anchored to the inner membrane by specialized proteins and stabilized by special cationic (positively charged) proteins called histones, the nucleolus found in the nucleus is where mRNA molecules are formed, which are formed into ribosomes which pass through the nuclear pores and function in the cytoplasm to synthesize proteins
• Cytoskeleton


  • Network of scaffolding formed from interacting protein filaments such as microtubules and microfilaments, gives the cell some internal structure and participates in transport of materials around the cell, constantly assembling and disassembling in various areas of the cell, prokaryotic cells do not have a cytoskeleton
• Mitochondria


  • "Energy factories" of the cell that require the oxygen we breathe, and they use it in the efficient metabolism of glucose and other molecules to produce energy in the form of ATP, most of the ATP in a eukaryotic cell is produced by the mitochondria, have a double membrane, and the inner membrane is extensively infolded to form cristae which act to increase the surface area available for enzymatic metabolic reactions, aerobic respiration is the most efficient and the major energy yielding process, and it takes place in mitochondria