CLASSIFICATION OF PATHOGENS ON THE BASIS OF RNA TYPING
CLASSIFICATION OF PATHOGENS ON THE BASIS OF RNA TYPING
Taxonomy The branch of biology concerned with the classification
of organism into groups based on the similarities of structure and
origin
OR
The scientific classification of organism into especially named
group on the basis of shared character or evolutionary relationship
inferred from fossil record or genetic analysis
Phylogeny A phylogeny is a representation of organisms based on
the evolutionary relationship
OR
The evolutionary history of a taxon is called phylogeny
Phylogenetic tree of lifePhylogenetic tree is a branching
diagram or tree showing the inferred evolutionary relationship
among various biological species based upon similarities and
difference in their physical and genetic character.
Classification system of organismUsually there are two
classification system
1. Five kingdom system.
Traditional system of classification of organism based on
similarities in their morphological, developmental and nutritional
character.
This system was proposed by the Robert Whittaker in 1969 on the
basis of
Cell type (simple or complex)
Their ability to make food
The number of cells present in their body
Five kingdom system
Three domain systemThree domain system of classification of
living organism was introduced by Carl Woese in 1977 on the basis
of molecular evidences ( small subunit 16s rRNA)
Structure of RibosomeRibosome is a complex structure composed of
rRNAs and proteins and is therefore called as ribonucleoprotein
Each ribosome has two subunit :
1. Smaller subunit bind to mRNA
2. Larger subunit bind to tRNA and amino acid Prokaryote
Prokaryote have 70s (Svedberg) ribosome having:
1. small 30s which have SSU 16s rRNA ( 1540 nucleotide and 21
r-protein)
2. Large 50s which have SSU 5s rRNA (120 nucleotide) and 23s
rRNA ( 2900 nucleotide) and 31 r-protein
Eukaryotes Eukaryotes have 80s ribosome that have:
1. Small 40s that have 18s SSU rRNA
2. Large 60s that have SSU 5s and 28s rRNA and 5.8s rRNA
RNA TYPING RNA typing is a culture independent technique which
involved the extraction of DNA or RNA followed by amplification of
16s rRNA encoding DNA (rDNA) or 16s rRNA for the identification,
classification and phylogenetic diversity.
16S rRNA gene sequence analysis is considered as gold standard
in the bacterial identification
Advantages of 16s rRNA Universal presence
Easy accessibility
PCR amplification
Rare lateral gene transfer
Broad coverage of taxa between domain and species
High informative nature and constant in function
Not enough variation
Not encode any virulence factor
Variable rate of change in sequence at different
positionSequence HomologyHomology between protein and RNA or DNA
sequence are described in terms of shared ancestry. Two segments of
DNA can have shared ancestry because of speciation or duplex event.
Sequence Homology is performed on the bases of DNA or RNA
In 1960 Sequence Homology on DNA bases is performed using mol%
G+C content or DNA-DNA hybridization according to which:
1. Two strain of distinct phenotype show >70% hybridization
are said to be members of same specie
2. Two strain of distinct phenotype show
