Prokaryotic cells

• Prokaryotic cells usually lack complex compartmentalization.
• Some prokaryotes do have specialized membranes that perform metabolic functions.
• Cyanobacteria, also known as 'blue-green' algae, contain chlorophyll a and use sunlight as an energy source through photosynthesis.
• Some cyanobacteria contain compounds that are toxins.
• The theory of endosymbiosis explains the origin of mitochondria and chloroplasts.
• Symbiosis is the close and often long-term interactions between different biological species.
• Although prokaryotic cells are structurally less complex than eukaryotes, they have specialised structures with specific functions.
• Prokaryote cells lack membrane-bound organelles, have a plasma membrane, contain ribosomes (70S), and can have flagella.
• Prokaryotes have a cell wall (bacteria: peptidoglycan), a generally single circular chromosome (bacteria sometimes more and they can be linear), and in archaea, the DNA is wrapped around histone proteins (not in bacteria).
• Prokaryotic cells are the focus of this session, with an emphasis on bacterial cells.
• By the end of this session, you should be able to describe the features of a typical bacterial cell, relate structure to function for the features of a bacterial cell, and understand in general how Archaea differ from bacteria.
• The Phylogenetic Tree of Life was discussed in a 2013 Special Paper of the Geological Society of America by Farmer, Jack.
• There are two main types of microscopes: Light microscopes and Electron microscopes.
• The resolution of a microscope depends on the wavelength of the beam being used, with the lower the wavelength leading to better resolution.
• In a light microscope (LM), visible light passes through a specimen and then through a system of glass lenses, which magnify the image.
• A compound microscope is a microscope fitted with two or more convex lenses, which have lower resolution than electron microscopes.
• Transmission electron microscopes (TEMs) use electromagnets to focus a beam of electrons through a specimen and are used to study the internal structure of cells, but can only use thin samples.
• Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D.
• Rods have a higher surface area and are better able to take up nutrients from the environment.
• Cocci are less prone to drying out.
• Spiral types are usually motile, and their shapes help them to move through aqueous environments.
• A polysaccharide or protein layer called a capsule covers many prokaryotes, this is external to the cell wall.
• In certain species capsules are important in contributing to bacterial virulence.
• All of the principal pathogens which cause pneumonia and meningitis, including Streptococcus pneumoniae, Neisseria meningitidis, Klebsiella pneumoniae, have capsules on their surface.
• Capsules can prevent white blood cells from engulfing bacteria, lysosomes from breaking down bacteria cells, anaerobic bacteria from getting oxygen toxicity, and can help a bacteria stick to a host cell of a 'biofilm' environment.
• Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella.
• The bacterial flagellum has three basic parts; basal body, hook and filament principally constructed of a protein flagellin.
• The flagellum rotates from the basal body.
• In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli such as chemotaxis, phototaxis.
• Some prokaryotes have fimbriae (also called attachment pili), which allow them to stick to their substrate or other individuals in a colony.
• Fimbriae are composed of a protein pilin.
• Sex pili are longer than fimbriae (usually only one or two per cell) and allow prokaryotes to exchange DNA.
• Conjugation is the process where genetic material is transferred between bacterial cells.
• Sex pili allow cells to connect and pull together for DNA transfer.
• Some of this DNA can become incorporated in the chromosome loop of the recipient cell and be transmitted to the daughter cells of future generations, altering the genotype permanently.
• Certain bacteria can produce spores, this occurs generally when stressed.
• Endospores are dormant forms and generally resistant to temperature, pH and other environmental factors.
• Endospores can germinate into new bacterial cells when conditions are suitable.
• In August 2016, in a remote area in Siberia, a 12-year-old boy died and at least 20 people were hospitalised after being infected by anthrax.
• The theory is a reindeer infected with anthrax died at least 70 years ago and its frozen carcass became trapped under a layer of frozen soil (permafrost).