Question

1. Please describe what the following molecules and structures tell scientists about the evolution of the three domains: flagella, nuclear membrane lipids, ribosomes, grana, cell membrane lipids, DNA genomes, mRNAs, and types of DNA polymerase.

Answer 1

The 3 domains are archaebacteria,Eubacteria and prokaryota .The flagella, nuclear membrane lipids, ribosomes, grana, cell membrane lipids, DNA genomes, mRNAs, and types of DNA polymerase are the major distinguishing characters between the 3 domains.

The phylogeny was based on differences in the nucleotide sequences in the ribosomal RNAs (rRNA), lipid structure of the cell membrane and the sensitivity of the cell towards the antibiotics.The rRNA molecules was the most important among these.These RNA molecules carry out the same function in all the organisms, but there is a variation in their structuures in the due course of time. The similarities and dissimilarities in rRNA nucleotide gives an idea about the closely related or unrelated organisma thereby helping in the phylogenetic relationship.

The different characters of these domains are

	Bacteria	Archea	Eubacteria
membrane bound organelles	absent	absent	present
Nucleous with a membrane bound nucleolus	Absent	Absent	Present
Cell wall	Present; Contains muramic acid	Contains cell wall made up of a variety of chemical substances except muramic acid	Plants have cell wall made up of cellulose
Polycistronic mRNA	Present	Present	Absent
Introns in mRNA	Absent	Absent	Present
Ribosome size	70S	70S	80S
RNA polymerase	Only one type seen	Several types seen	3 Types. RNA polymerase I,II,III

Genome	Circular DNA	Circular DNA	Linear chromosomes
Histones	Absent	Present	Present