Tuesday, January 6, 2009

Hello 2009, Origins 1

The new year is a good time to start looking at the beginning of life, which we call Origin of Life studies, or OOL. There are several ways to classify the structures of living organisms. We will use the 3-domain system here, which divides into organisms of these types: Archaea, Bacteria and Eukaryotes. Pictures of these three are on this page.

The archaea (pronounced are-KEY-a) can make their own food, reproduce and create their own energy. These are single-celled organisms which were thought to be ancestors to bacteria. But when their entire genome was first sequenced in 1996, it was found they were not directly related to bacteria. So, they were put in a different domain of life. Some scientists think these archaea were present on Earth at 3.8 to 3.85 billion years ago.

I think everyone knows what bacteria are. They live everywhere and can cause diseases of different sorts. We will use the example of Cyanobacteria, since they are considered the first known bacteria on the Earth. Cyanobacteria are able to live on their own, unlike some bacteria which are known as parasites and can't make their own food. We use these because we can determine what is necessary for life to appear and then have a steady supply of food made from photosynthesis, which takes sunlight and water to create sugar and building supplies for the organism.

The last is called a Eukaryote (pronounced you-CARry-oat) and is what is known as a "true cell." The others are cells too, but they don't have as many of the complex organs that the eukaryote has. There are some single-celled organisms that are eukaryotes, such as the one that causes malaria, called Plasmodium. Also, the multi-celled plants and animals, including humans, are made of these eukaryotic cells.

These three types of cells are the earliest that we know, since they are still living on the planet. Scientists used to think these three domains were part of the evolutionary progress from simple to complex. For example, they thought at one time that bacteria were first, then over millions of years became slowly more complex and eventually gave rise to eukaryotes. But because the molecular structue is so different from each other, it was determined that they did not start with one and lead to another by Darwinian processes (small change and selection). These discoveries can be read here in a paper by the National Center of Biotechnical Information (NCBI).

Some believe the three domains had a common ancestor. If so, that ancestor would have had to have certain qualities. The ancestor is known as LUCA (last unknown common ancestor). I will get into more details in upcoming posts.

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