The document discusses the three domains of life: Archaea, Bacteria, and Eukarya. Archaea are prokaryotic cells characterized by membrane lipids with ether linkages that allow them to withstand extreme temperatures. Bacteria are also prokaryotic but have phospholipid bilayers in their membranes. Eukarya include organisms with membrane-bound organelles like the nucleus and are represented by five kingdoms including plants, animals, and fungi.

1. THREE DOMAINS OF LIFE
By:
K.sanjay,
I M Sc Microbiology[BP211525],
Sacred Heart College[Autonomous],
Tirupattur.
To:
Dr.P.Saran Raj,
Head of Department of Microbiology,
Sacred Heart College[Autonomous],
Tirupattur.

2. Discovered by:
The term “Domain” was introduced by American
Microbiologist and biophysicst carl woese et al
[1990] together with the proposal of a natural
classification system for all life on earth
,including microorganisms, which had previously
escaped any attempt of classification based on
evolutionary relationships.

3. Organisms can be classified into one of three domains
based on differences in the sequences of nucleotides
in the cell's ribosomal RNAs (rRNA), the cell's
membrane lipid structure, and its sensitivity to
antibiotics. The three domains are the Archaea, the
Bacteria, and the Eukarya.
Three Domains of Life:

4. Archaea are prokaryota cells, typically characterized by membrane lipids
that are branched hydrocarbon chains attached to glycerol by ether
linkages. The presence of these ether linkages in Archaea adds to their
ability to withstand extreme temperatures and highly acidic conditions,
but many archaea live in mild environments. Halophiles, organisms that
thrive in highly salty environments, and hyperthermophiles, organisms
that thrive in extremely hot environments, are examples of Archaea.[1]
Archaea evolved many cell sizes, but all are relatively small. Their size
ranges from 0.1 μm to 15 μm diameter and up to 200 μm long. They are
about the size of bacteria, or similar in size to the mitochondria found in
eukaryotic cells. Members of the genus Thermoplasma are the smallest
of the Archaea
Archaea:

5. Even though bacteria are prokaryotic cells just like Archaea, their
membranes are made of phospholipid
bilayers. Cyanobacteria and mycoplasmas are two examples of bacteria.
They characteristically do not have ether linkages like Archaea, and they are
grouped into a different category—and hence a different domain. There is a
great deal of diversity in this domain. Confounded by that diversity
and horizontal gene transfer, it is next to impossible to determine how many
species of bacteria exist on the planet, or to organize them in a tree-structure,
without cross-connections between branches.
Bacteria:

6. Members of the domain Eukarya—called
eukaryotes—have membrane-bound
organelles (including a nucleus containing
genetic material) and are represented by
five kingdoms: Plantae, Protozoa, Animalia, C
hromista, and Fungi.
Eukarya: