bacteria
IN THE BEGINNING...
Scientists predict that our home, planet Earth, probably formed about 4.6 billion years ago. Around 4.3 billion years ago, the Earth began to cool, allowing land, water and the atmosphere to develop.
Early Earth was wrought with active volcanoes and asteroid strikes. The oldest traces of what might be considered "life" are 3.8 billion years old. However, these entities (chemofossils) are so foreign to what we consider to be "living" today, scientists are still debating on if these chemofossils can be considered a true life-form. This chemofossil was found nestled inside 3.8 billion year old rock found in Greenland. The fossil contained phosphatic minerals and carbon. Living organisms have a characteristic ratio of carbon-12 to carbon-13 (this is what allows for dead organic matter to be carbon-dated). This chemofossil exhibited the characteristic carbon-12 to carbon-13 ratio characteristic of once living organisms!
Early Earth was wrought with active volcanoes and asteroid strikes. The oldest traces of what might be considered "life" are 3.8 billion years old. However, these entities (chemofossils) are so foreign to what we consider to be "living" today, scientists are still debating on if these chemofossils can be considered a true life-form. This chemofossil was found nestled inside 3.8 billion year old rock found in Greenland. The fossil contained phosphatic minerals and carbon. Living organisms have a characteristic ratio of carbon-12 to carbon-13 (this is what allows for dead organic matter to be carbon-dated). This chemofossil exhibited the characteristic carbon-12 to carbon-13 ratio characteristic of once living organisms!
All Early Organisms Were Prokaryotic
Cyanobacteria (a type of prokaryotic organism) were among the first organisms to exist on planet Earth (3.5 Billion Years Ago)
Fossilized Cyanobacteria
Scientists have discovered fossils of prokaryotic organisms that lived as far back as 3..5 billion years ago. Prokaryotic organisms are organisms that are made up (almost exclusively) of a single prokaryotic cell. The vast majority of prokaryotic organisms are microscopic, meaning that they are only visible with the aid of a microscope. For this reason, prokaryotic organisms are called "microbes".
Cyanobacteria
The oldest fossils we currently have on record are of cyanobacteria, formerly called "blue-green algae". Before more was known about these organisms, they were called blue-green algae, because of their resemblance to true algae. However, cyanobacteria are not algae at all, but far from it! Algae are considered eukaryotic and are made up cells that are very different from the cyanobacteria.
Cyanobacteria are prokaryotic organisms that are made up of prokaryotic cells. Prokaryotic cells lack a nucleus and lack membrane-bound organelles. In contrast, algae are eukaryotes that are made up of eukaryotic cells. Eukaryotic cells contain a nucleus and membrane-bound organelles.
Cyanobacteria are prokaryotic organisms that are made up of prokaryotic cells. Prokaryotic cells lack a nucleus and lack membrane-bound organelles. In contrast, algae are eukaryotes that are made up of eukaryotic cells. Eukaryotic cells contain a nucleus and membrane-bound organelles.
• Microbes: 3.8 billion years ago (bya)
• Eukarya: 2 billion years ago (bya)
• Multicellular: 0.5 billion years ago (bya)
• Eukarya: 2 billion years ago (bya)
• Multicellular: 0.5 billion years ago (bya)
Prokaryotic cells existed from about one-billion years before eukaryotic single-celled organisms evolved. Prokaryotic cells are almost always smaller than eukaryotic cells. Prokaryotic cells lack membrane-bound organelles and do not have a nucleus. In contrast, eukaryotic cells do have a nucleus and do have membrane-bound organelles.
Prokaryotic cells existed from about one-billion years before eukaryotic single-celled organisms evolved. Prokaryotic cells are almost always smaller than eukaryotic cells. Prokaryotic cells lack membrane-bound organelles and do not have a nucleus. In contrast, eukaryotic cells do have a nucleus and do have membrane-bound organelles.
Bacteria
Most prokaryotic organisms are bacteria. All bacteria cells contain cytoplasm, a cell membrane (also called the plasma membrane) and genetic material.
Illustration Showing the Anatomy of a Typical Bacteria Cell
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Cross-Section of a Bacterial Cell
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Prokaryotic cells Do Not Have
Prokaryotic cells Do Have
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E. Coli Bacteria
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Shapes of Bacteria
Bacteria usually take on only a few different shapes (morphologies) and arrangements.
The common morphologies for bacteria cells include coccus, bacillus, spirillum, coccobacillus, vibrio and spirochete. See illustrations below!,
The common morphologies for bacteria cells include coccus, bacillus, spirillum, coccobacillus, vibrio and spirochete. See illustrations below!,
The round bacteria cells are called Cocci (plural) or Coccus (singular).
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Rod-shaped bacteria cells are called Bacilli (plural) or Bacillus (singular).
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The short rod-shaped bacteria cells are called Coccobacillum (plural) or Coccobacillus (singular).
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The loose helical spiral-shaped bacteria cells are called Spirochettes (plural) or Spirochette (singular).
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Bacteria cells typically arrange themselves with other bacteria cells to form certain arrangements. Some of the more common arrangements bacteria form will be briefly described here.
The arrangements for the round bacteria (cocci) include the coccus the diplococcus, the tetrad, the streptococcus and the staphylococcus.
The arrangements for the round bacteria (cocci) include the coccus the diplococcus, the tetrad, the streptococcus and the staphylococcus.
The coccus refers to the arrangement of a single coccus.
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The diplococcus occurs when 2 cocci arrange themselves side-by-side.
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The tetrad describes the arrangement of 4 cocci in the shape of a square.
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Cocci are also commonly seen forming clusters with other cocci. A cluster of cocci is called staphylococcus. |
Cocci are also commonly seen forming chains with other cocci. A chain of cocci is called streptococcus
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The rod-shaped bacteria also form chains.
(See illustrations below!)
(See illustrations below!)
A chain of bacilli is called streptobacillus.
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A single rod-shaped bacteria is called a bacillus.
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THE NUCLEOID
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Prokaryotic cells do not have a true nucleus, but they do have genetic material. The genetic material of prokaryotic cells exists in a region called the NUCLEOID. The nucleoid IS NOT surrounded by a membrane, while the nucleus of eukaryotic cells IS surrounded by a membrane.
The genetic material of the nucleoid is very different from the genetic material found in eukaryotic cells. The DNA of prokaryotic cells usually consists of a single circular chromosome. In addition to this single chromosome, many prokaryotic cells also carry a small, circular, segment of double-stranded DNA that is considered extrachromosomal. This piece of extrachromosomal DNA is called a plasmid.
The DNA of archaea has histones (as do eukaryotes), whereas the DNA of bacteria lack hostones. |
Illustration of the Nucleoid and the Genetic Material of a Typical Prokaryotic Cell.
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