Remy Neville
Professor David Morris
Introductory Microbiology (BISC 2337-10)
7 February 2013
First Examination
1. a) The bacterium Caulobacter crescentus has a prokaryotic cytoskeleton with three key elements. The first structural element depicts FtsZ, which is hypothesized to play a role in division in bacterial cells. Its eukaryotic counterpart is tubulin (though it is also similar to the actin-myosin contractile ring), seen in their 3-dimensional structures. Monomeric FtsZ is bound to GTP and polymerizes with other FtsZ monomers with the hydrolysis of GTP in a mechanism similar to tubulin dimerization. FtsZ forms a filamentous ring structure located in the middle of the cell called the Z-ring that constricts during cell division. The Z-ring is a highly dynamic structure that consists of numerous bundles of protofilaments that extend and shrink. FtsZ acts as an organizer protein and is required for cell division. It is the first component of the septum during cytokinesis, and it recruits all other known cell division proteins to the division site.
The second elemental structure is MreB—thought to function in polarity, this bacterial protein is analogous to eukaryotic actin. They are similar in their 3-D structures (much like FtsZ and tubulin) and filament polymerization. Almost all non-spherical bacteria rely on MreB to determine their shape. MreB assembles into a helical network of filamentous structures just under the cytoplasmic membrane, covering the whole length of the cell. MreB determines cell shape by mediating the position and activity of enzymes that synthesize peptideglycan and by acting as a rigid filament under the cell membrane that exerts outward pressure to sculpt and bolster the cell. MreB condenses from its normal helical network and forms a tight ring at the septum right before cell division, a mechanism that is believed to help locate its off-center septum. MreB is also important for polarity determination in polar bacteria, as it is responsible for the correct positioning of at least four different polar proteins.
And finally, crescentin (encoded by CreS gene) plays a role in shape, and the eukaryotic counterparts are intermediate filaments. Crescentin has a rather large primary homology with IF proteins in addition to three-dimensional similarity. Crescentin forms a continuous filament from pole to pole alongside the inner, concave side of the crescent-shaped bacterium. Both MreB and crescentin are necessary for C. crescentus to exist in its characteristic shape; it is believed that MreB molds the cell into a rod shape and crescentin bends this shape into a crescent.
b) The bacterial specimen stained with malachite green and safranin shows rod-shaped bacterium in clusters with endospores (the small oval shaped spots.) This indicates that the genus is probably Gram-positive Bacillus (with thick cell walls). To confirm my hypothesis, a catalase test could be performed. Bacillus should test positive for the enzyme (fizzing upon contact). Also, they should be aerobic and need oxygen to thrive.
2. Abu-Bakr Muhammad Al-Razi earned the title of the first physician in the medieval world. Al-Razi’s tactic of seeking the area of Baghdad where the putrefaction of meat took the longest (to build his hospital) shows an early appreciation of the relationship between disease and something in the air. He concluded that the healthiest part of the city was where the meat spoiled the slowest. Al-Razi’s concept was based on what is now known as contagious disease; infectious microbes can travel through the air, for example, after someone nearby sneezes or coughs. It was also an early predecessor to the Germ theory of disease. This says that small organisms (called germs), known as microbes, cause diseases. Most, but not all diseases are infectious. Many scientists and doctors in history figured out that microscopic organisms cause diseases. Even after the microscope was invented,