Domain Bacteria and Archaea

Prokaryotes:

Microscopic life covers nearly every square centimeter of Earth. There are microorganisms of many different sizes and shapes, even in a drop of pound water. The smallest and most common microorganisms are prokaryotes--- single-celled organisms that lack nucleus.

Prokaryotes typically range in size from 1 to 5 micrometers, making them much smaller than most eukaryotes cells, which generally range from 10 to 100 micrometers in diameter.

The Domains bacteria and archaea share many similar characteristics because they both descended from a common ancestor. But at some point the archaeas and the bacteria segregated due to many factors. Once they were separated they developed new characteristics that made them unique.

Eubacteria:

The larger of the two kingdoms of prokaryotes is the eubacteria. Eubacteria includes a broad range of organism with different life styles. Eubacteria live almost everywhere. Some live in the soil, while others infect large organism and cause disease. Like other prokaryotes, eubacteria are usually surrounded by a cell wall that protects the cell from injury and determines its shape. The cell walls of eubacteria contain peptidoglycan, unlike the archaea. Within the cell wall is a cell membrane that surrounds the cytoplasm. Some eubacteria have a second, outer, membrane.

Archaebacteria:

By just looking at archaebacterias they might seem exactly like the eubacterias. Although they share many similarities such as the lack of nuclei, there are some characteristics that make them unique. Archaebacteria lack peptidoglycan, a carbohydrate found in the cell walls of eubacteria, and their membrane lipids are quite different. Also, their DNA sequences of key archeabacterial genes are more like those of eukaryotes than those of eubacteria. Many scientists think that archaebaceria may be the ancestor of eukaryotes.

Archaebacteria normally live in very extreme environments. One group of archaebacteria is the methanogens, prokaryotes that produce methane gas. Methanogens live in oxygen-free environments, such as thick mud and the digestive tracts of animals. Other kinds of archaebacteria live in extremely salty environments, such as Utha’s Great Salt Lake, or in hot springs where temperatures approach the boiling point of water.

Prokaryotes – General Characteristics: How to identify a prokaryote?

Prokaryotes can be identified by their shapes, the chemicals in their cell walls, their way to move, and the ways they obtain energy.

Shapes: Prokaryotes can arrange themselves in many different ways. Rod-shaped prokaryotes are called bacilli. Spherical prokaryotes are called cocci. Spiral and corkcrew-shaped prokaryotes are called spirill.

Cell Walls: There are basically two different types of cell walls among prokaryotes. Eubacteria has cell wall with peptidoglycan. On the other hand, Archaebacteria don’t have peptidoglycan in their cell wall.

Movement: Prokaryotes can also be identified by the way they move. Some use flagella, whip-like structures used for movement. Others just snake, lash or spiral forward. Many prokaryotes do nor move at all.

Introduction

Life is anywhere on earth, you can find living organisms from the poles to the equator, from the bottom of the sea to several miles in the air, from freezing environments to dry valleys. Over around 3.7 billion years or so, living organism on Earth have diversified and adapted to almost every possible environment. All living organism do hare certain similarities, which they probably inherited from a common ancestor. All living organism can replicate, and the replicator molecule is DNA. All living organisms have the ability to convert the information stored in DNA into products used to build things like fats, proteins and carbohydrates.

In the early 1970’s a professor in the Department of Microbiology named Dr. Carl Woese and other scientists began to find evidence for a previously unknown group of prokaryotic organism. These organisms lived in extreme environments - deep sea hydrothermal vents, "Black smokers", hot springs, the Dead Sea, acid lakes, salt evaporation ponds - environments that scientists had never suspected would contain a profusion of life!

Because they appeared prokaryotic, they were considered bacteria and named “Archaebacteria” (ancient bacteria). However, became obvious from biochemical characteristics and DNA sequence analysis that there were numerous differences between these archaebacteria and other bacteria. It was realized that these archaebacteria were more closely related to the eukaryotes than to bacteria. From this work, Dr. Woese proposed that there should be a new caterogy of classification of life - the Domain, a classification category above Kingdom.