Foundations-Cells-2

From CellBiology

Introduction to Prokaryotes


This lecture is also an introduction to cell compartments and describes the structure of membranes forming these compartments.


Draft - this online lecture is currently in 2018 draft status. This notice removed when completed.
Cells and Membranes: 1 Cells and sizes | 2 Prokaryotes | 3 Viruses and prions | 4 Plasma membrane | 5 Compartments | 6 Membrane structure | 7 Membrane specialisations | Foundations - Moodle

Terms

  • Archaea - prokaryote single-celled microorganism with no cell nucleus or any other membrane-bound organelles. Archaea were initially classified as bacteria.
  • Bacteria - Prokaryotes.
  • Commensal bacteria - (normal microflora, indigenous microbiota) micro-organisms present on body surfaces covered by epithelial cells exposed to the external environment (gastrointestinal and respiratory tract, vagina, skin, etc.).
  • Compartments - separate sections or part of a structure either as a physical compartment (membrane bound) or functional compartment (no membrane).
  • Eukaryote - cells containing a nucleus.
  • Flora - (microflora) bacteria and microscopic algae and fungi living in a particular anatomical site or habitat.
  • Gut - (intestine)
  • Micron - (micrometre) is one millionth of a metre. (1 x 10-6)
  • Nucleus - the double membrane compartment containing chromosomes within all eukaryotic cells.
  • Plasma membrane - (cell membrane) the lipid bilayer containing proteins and cholesterol that encloses each cell.
  • Prokaryote - single-celled microorganism with no cell nucleus or any other membrane-bound organelles.

Divisions of Life

Prokaryotic

  • bacteria and archaea (single-celled microorganisms previously called archaebacteria)
    • no cell nucleus or any other organelles within their cells
    • organisms that can live in extreme habitats Archaea

Eukaryotic

File:Leukocyte phagocytosis of yeast
  • cell nucleus
  • plants, animals, fungi, protists

Unicellular and Multicellular

  • Unicellular
    • All prokaryotes and some eukaryotes (Yeast + budding, non-budding)
    • Protozoa + classified by means of locomotion: flagellates, amoeboids, sporozoans, ciliates + often "feed" on bacteria
  • Multicellular
  • Eukaryotes - Plants and Animals
  • Allowed development of specialized cells, functions and tissues


Karyote from the Greek, Karyose = kernel, as in a kernel of grain; referring to the presence or absence of a nucleus.

Prokaryote

Escherichia coli.jpg

Escherichia coli

Gram-positive Micrococcus luteus bacteria.jpg

Micrococcus luteus bacteria

Bacteria_morphology

Bacteria shape (basis of naming)

Bacterial morphologies.jpg

Bacterial morphologies

  • evolutionarily arose first (3.5 billion years ago) Evolution of Cells
  • bacteria are biochemically diverse and smaller, approx 2 x 1 micron (1x10-6 m)
  • simple structure, classified by shape (rod-shaped, spherical or spiral-shaped)
  • some prokaryotic cells have also been shown to have a "cytoskeleton", which is different from eukaryotic cells.
  • some bacteria are highly motile
Bacteria motility movie 1.jpg
 ‎‎Bacteria Motility
Page | Play


Not all bacteria are dangerous or disease causing - The adult human in addition bacteria to the skin surface and lining of the respiratory/digestive tract, also has intestines contains trillions of bacteria made up from hundreds of species and thousands of subspecies)

Prokaryotes Cell Wall

Prokaryote cell cartoon
  • Bacterial Shape - Bacterial shapes and cell-surface structures
  • Bacterial Membranes - A small section of the double membrane of an E. coli bacterium
    • Bacterial outer membranes - outer membrane contains porins
  • Bacterial cell walls - Bacterial cell walls
    • Gram-negative bacteria surrounded by a thin cell wall beneath the outer membrane
    • Gram-positive bacteria lack outer membranes and have thick cell walls

(MH - note that some unicellular eukaryotes can also have a cell wall)

  • Antibiotics - inhibit either bacterial protein synthesis or bacterial cell wall synthesis Antibiotic targets Gram-positive and Gram-negative bacteria

Bacterial Replication

This speeded up movie shows the process of bacterial cell division. Note the cells grow in size and then divide, this process is called "binary fission".



The lefthand image is bright field microscopy the righthand image is fluorescence microscopy of the same cells.


This second movie runs at real time showing just how quickly bacteria can divide!


Links: Molecular Biology of the Cell Figure 25-4. Bacterial shapes and cell-surface structures | Figure 11-17. A small section of the double membrane of an E. coli bacterium | Medical Microbiology Figure 2-6. Comparison of the thick cell wall of Gram-positive bacteria with the comparatively thin cell wall of Gram-negative bacteria

Prokaryote Mycoplasmas

  • smallest self-replicating organisms, smallest genomes (approx 500 to 1000 genes)
  • spherical to filamentous cells, no cell walls
  • surface parasites of the human respiratory and urogenital tracts
    • Mycoplasma pneumoniae infect the upper and lower respiratory tract
    • Mycoplasma genitalium a prevalent sexually transmitted infection
    • Mycoplasma hyorhinis found in patients with AIDS


Links: The Cell- A Molecular Approach | Table 1.1. Prokaryotic and Eukaryotic Cells | Antibiotic Inhibitors of Protein Synthesis | Molecular Cell Biology Figure 12-6. DNA replication and cell division in a prokaryote | Biochemistry Figure 28.15. Transcription and Translation two processes are closely coupled in prokaryotes, whereas they are spacially and temporally separate in eukaryotes.


Draft - this online lecture is currently in 2018 draft status. This notice removed when completed.
Cells and Membranes: 1 Cells and sizes | 2 Prokaryotes | 3 Viruses and prions | 4 Plasma membrane | 5 Compartments | 6 Membrane structure | 7 Membrane specialisations | Foundations - Moodle