What are Prokaryotes?


Cells can be classified into prokaryotes and eukaryotes. Prokaryotes are considered to be the first ever living cells, and are thought to have originated from protobionts. They are in the kingdoms of monera (simple bacteria) and archaea. Fossils proved us that both archaea and monera had evolved somewhere between 3 to 4 billion years ago.Staphylococcus, escherichia coli, and streptococcus are examples of prokaryotes.

The structure of a Prokaryote cell:


Why were they the first form of life to appear on earth?


There are several theories suggesting how life first appeared on earth.
  • Extraterrestial: There is evidence that suggests that life did not originate from earth, but from outer space. In 1969, am meteorite landed near Allende, Mexico. After close observation of the meteorite, the meteorite was said to contain amino acids, a molecule that is used to create proteins, the basics of all life. This theory of cosmic ancestry is known as "Panspermia". Panspermia is a hypothesis that states that the origins of life already existed in the universe, and that life on Earth originated from the same 'seeds' as other life in the universe.
  • Supernatural: Although this is not considered a scientific theory, as science attempts to collect accurate, and tangible data, there are people who believe that the origin of life is outside science.
  • Organic Chemical Evolution: Before the 1800's, scientists were on the assumption that organic material could only be formed by living things. However, in the mid 1800's, a French scientist discovered that when he heated crystals of a mineral (A mineral is defined to be something inorganic), it formed urea, a organic substance when it cooled. Aleksandr Ivanovich Oparin, was a Russian biochemist, who attempted to discover the origins of life on Earth. In the year 1922, he hypothesized that life on Earth originated from a period of Chemical Evolution. Because the newly formed Earth had conditions very different from the world today, Oparin hypothesized that simple organic and inorganic materials may have combined to form complex organic compounds, which might have formed the first living organisms, such as the prokaryote.

To prove Aleksandr Oparin's hypothesis, Stanley Miller, a graduate student in the 1950's, designed a experiment.
moz-screenshot.jpgexternal image Millers_1.gif
His experiment used simple inorganic compounds such as hydrogen gas, Nitrogen gas, Carbon Dioxide, Water, Ammonia, and Methane, as Oparin's original hypothesis stated that there was little free oxygen, and plenty of Nitrogen, Carbon, and Hydrogen.

Millers Experiment

external image MILLER%27SEXP.gif
The diagram above is a diagram of the apparatus of Miller's experiment. It attempts to use the inorganic substances as mentioned in the previous diagram, and recreate the atmosphere and conditions of the Earth when it first formed.

Prokaryotes and Eukaryotes, What are the Similarities and Differences?


Billions of years ago, during proterozoic period, prokaryotes came into existence and were the only form of life on earth. Over a period of time, prokaryotes evolved into more advanced cells, also known as eukaryotes.Biologists believe that eukaryotes evolved from prokaryotes because of the following similarities:
  • Both use RNA and DNA are the genetic material
  • Both use the same 20 amino acids
  • Both have ribosomes and DNA and RNA
  • Both have a lipid bilayer cell membrane.
  • Both use L amino acids and D sugars

The following are differences between prokaryotes and eukaryotes:
  • Prokaryotes are mostly unicellular (able to exist as a single cell or on their own) while most of the eukaryotes are multicellular.
  • Prokaryotes maintain their genome in a single copy, usually a single DNA chromosome, with as much information packed onto it as possible.
  • Many eukaryotes have two copies, divide the information up into several DNA chromosomes, with the genes packed relatively sparsely. Unlike prokaryotes, eukaryotes keep backup copies.
  • Having only one copy of a gene means that if an error is made, that damage is permanent-there is no backup copy for its rescue.

In addition, prokaryotes have:
  • No nucleus
  • No nuclear membrane (genetic material dispersed throughout cytoplasm)
  • No membrane-bound organelles
  • Simple internal structure
  • Most primitive type of cell (appeared about four billion years ago)

Diagram showing both prokaryote and eukaryote:

allcell.jpg

How did they obtain their energy initially? And after time for evolutionary change?


Before oxygen gas appeared on the earth's atmosphere, the earliest organisms could obtain their energy only through the anaerobic process. Anaerobic process is a process from which air or oxygen not in chemical combination is excluded.Fermentation of organic compounds is an anaerobic process and is the simplest type of biological energy yielding process.

The Process of fermentation
fermentation1420.JPG

What effects did they have on the physical chemistry of the earth in the long term?


Bibliography

Cells: Origin http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookCELL1.html

Aleksandr Oparin http://www.britannica.com/eb/article-9057170/Aleksandr-Oparin

Origin of Eukaryotes http://www.gwu.edu/~darwin/BiSc151/Eukaryotes/Eukaryotes.html

Were Bacteria The First life Froms On Earth? http://www.actionbioscience.org/newfrontiers/jeffares_poole.html

Microbial Population Explosion http://whyfiles.org/shorties/count_bact.html

Prokaryotes, Eukaryotes, and Viruses Tutorial http://www.biology.arizona.edu/cell_bio/tutorials/pev/page2.html

Introduction to the Protozoic Era http://www.ucmp.berkeley.edu/precambrian/proterozoic.html

Morphology of the Archaea http://www.ucmp.berkeley.edu/archaea/archaeamm.html

Kingdom Monera: The Prokaryotes http://fig.cox.miami.edu/Faculty/Dana/monera.html