Essay 7: On Prokaryotes

Prokaryotes are one of the two classifications of living cells. They are distinguishable from the other type, the eukaryotes by several characteristics. They don’t have a nucleus, which is where their name, pro, meaning before, and karyon, meaning nut or kernel, comes from. They lack organelles, their DNA is in a loop, whereas in eukaryotes it is in a bundle called a chromosome, they are much smaller than eukaryotes, and all multicellular organisms are comprised solely of eukaryotic cells.

Prokaryotes have very diverse refueling processes. Some are heterotrophs, others are autotrophs or chemotrophs. Some can even employ more than one technique to get the job done. Photoheterotrophs use photosynthesis, but get their carbon from organic compounds. Some prokaryotes need oxygen for respiration, and are called obligate aerobes. Other prokaryotes, called obligate anaerobes, will die if they come into contact with it. And still more called facultative anaerobes can use oxygen when it is available, and perform fermentation or anaerobic respiration when it is scarce.

Prokaryotes are able to move using a whip-like tail called a flagellum. The prokaryotic flagellum is a highly complex piece of bio-machinery comprised of 42 different types of protein. The flagellum can propel some prokaryotic species at 50 body lengths per second through the matrix in which they exist. That is the equivalent of a person swimming at 190 miles per hour through concrete. About 50% of prokaryotes are able to move towards favorable stimuli, and away from unfavorable stimuli.

Some prokaryotes are able to communicate with each other through cell signaling. Prokaryotes use this “language” to coordinate action among other members of their species. This allows for the formation of symbiotic colonies of prokaryotic cells. They can form filaments, in which some cells fix nitrogen for other cells, who in turn eliminate oxygen that would inhibit fixation. They can also form biofilms, and the members of these biofilms can signal to other cells to join them. Prokaryotes can also take information from their environment and store it as genetic code. They can later join with another cell and share this genetic material and the information which it contains through a tube called a pilus.

Extremophiles are prokaryotes that favor intense conditions. Thermophiles are exremeophiles that have special proteins that can withstand denaturing under high temperatures (113-251 degrees Fahrenheit). Psychrophiles can survive in extremely cold environments at or below five degrees Fahrenheit, such as permafrost,  polar ice, etc. There are radioresistants, which can withstand high radiation, piezophiles, which can survive high pressures, halophiles, which will die in salinity below 9% (triple the ocean’s salinity), acidophiles which thrive in pH levels below 3, and many, many more.

Prokaryotes are some of the most fascinating organisms on our planet. Some can use multiple refueling processes, some can survive environments that would kill most other organisms. There are also some 1000 species living inside us, without which we would not be able to survive.



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