M1 Discussion: An Ancient Eukaryote 6767 unread replies.107107 replies. Protozoa
ID: 96772 • Letter: M
Question
M1 Discussion: An Ancient Eukaryote
6767 unread replies.107107 replies.
Protozoan parasite, Giardia lamblia, causes acute gasteroenteritis called Giardiasis. This primitive eukaryote has a distinct nucleus, no mitochondria, and no recognizable endoplasmic reticulum or Golgi apparatus. It is quite possible that G. lamblia belongs to an ancient lineage that separated from the rest of the eukaryotes before mitochondria were acquired or internal membranes were developed. The other possibility is that G. lamblia lost its organelles during the course of its evolution as it adapted to its parasitic lifestyle.
Describe (in 250-300 words) how you might use nucleotide sequence comparisons to distinguish between these possibilities.
Explanation / Answer
Giardia lamblia has a very interesting organism in evolutionary sense. The organism is an eukaryote but it lacks mitochondria, no recognizable endoplasmic reticulum or Golgi apparatus. There are two possibilities for the absence of these crucuial organelles. 1. It might have diverged from early eukaryotes and hence the mitochondrial evolution did not take place. 2. It might have lost the pre existing mitochondria due to its lifestyle changes.
The use of sequence information and genetic analysis has led us to explore more about this species. We can use this information in following ways.
The sequening of the genome and annotation of different proteins has cleared the picture about the evolutionary origin of the organism. The genes which code for the homologes of mitochondital proteins like HSP 70 and chaperonin express throughout the life cycle except during excystation. This suggests thar the organism once had the mitochondria and later lost it during parasitic life. Similarly the genes coding for the aly-tRNA synthetase (ValRS) are found in the G. lambia. This gene is believed to be originated from mitochondria. It again suggests that the organism is not pre-mitochondrial in evolution. Recently, in 2012, the complex cellular machineries like localized, mitochondria-like electron-transport machinery have given more proofs that the mitochondria where once present in the organism.
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