Chapter 17, Problem 33A

Summary Introduction

To write:

An argument for or against the inclusion of Eubacteria and Archaea in the same domain and its effects on the phylogenetic tree of life.

Introduction:

The phylogenetic tree of life consists of two major categories:

• Prokarya.
• Eukarya.

Explanation of Solution

Gene sequencing is a major technique which may be used as an evidence to determine the bacterial phylogeny. The chemical fossils of unique lipids may be used as a source of information.

Through gene sequencing, it has been determined that archaebacetria evolved earlier 0

Thus, the archeal lineage may be considered as the oldest and most ancient existence on Earth.

The eubacteria are characterized by a rigid cell wall, in contrast to the peptidoglycan molecules (except methanobacteria, which has pseudopeptidoglycan in their cell wall) found in archaebacteria.

Both Eubacteria and Archaea cannot be placed in the same domain. The major differences can be specified as follows:

• Archaea are simple organisms which originated on the Earth about 4 billion years ago. Eubacteria, on the other hand, are known to have complex structures.
• The cell wall of Archea a made of peptidoglycan molecules. The cell wall of Eubacteria is made of peptidoglycan along with lipopolysaccharide and muramic acid.
• The lipid membranes of Archaea have aliphatic acids. The cell wall of Eubacteria has ester bonds with fatty acids in their lipid membrane.
• Archaea do not follow Kreb’s cycle or the glycolysis pathway to break down glucose, whereas Eubacteria is known to follow them

If both Eubacteria and Archaea were to be included in the same domain, the phylogenetic tree of life will be changed considerably. All organisms will have evolved from this common domain or the Eukarya. Thus, all the different forms of bacteria will have originated from a single domain while the rest of the eukaryotes would belong to the Eukarya.

Conclusion

Both Eubacteria and Archaea cannot be placed in the same domain due to the considerably high differences in their structures and functioning.