BLAST Basic local alignment search tool

1. BLAST
Kishan Sharma
M.Sc. 2nd Year
Biotechnology
Manipal University
Jaipur

2. BLAST
 Basic Local Alignment Search Tool
 It is a sequence similarity search program for comparing
biological sequences such as amino acid sequence of
different proteins or the nucleotides of DNA sequences with
sequence database or library sequences.

3. BLAST
 BLAST was designed by Eugene Myers , Samuel Karlin ,
Stephen Altschul, Warren Gish, David J. Lipman and Webb
Miller at the National Institute of Health and was published in
Journal of Molecular Biology in 1990.
 It was originally developed & controlled by NCBI .
 Link: http://www.ncbi.nlm.nih.gov/BLAST/

4. BLAST
 Sequence alignments provide a powerful way to compare
sequences with previously characterized genes.
 Both functional and evolutionary information can be inferred from
well designed queries and alignments.
 The BLAST detects local as well as global alignments and regions
of similarity in unrelated proteins can be detected.

5. BLAST

6. BLAST types
 Blastp : compares protein query against proteins sequence
database.
 tBlastn : Compares a protein query sequence against a
nucleotide sequence database.
 Blastn : compares nucleotide query against nucleotide
sequence database.

7. BLAST types
 Blastx : Compares a nucleotide query sequence translated in
all reading frames against a protein sequence database.
 This option may be used to find potential translation
products of an unknown nucleotide sequence.
 tBlastx : compares nucleotide query against translated
nucleotide sequence database.

8. BLAST
 All BLAST programs use a substitution scoring matrix (BLOSUM or
PAM), determines pair-wise alignment scores.
 BLAST finds homologous sequences , not by comparing either
sequences in its entirety, but rather by locating short matches
between the two sequences.

9. NCBI Home page

10. NCBI-BLAST Home Page

11. Applications of BLAST
 Identifying Species: With the use of BLAST, you can possibly correctly
identify a species and/or find homologous species.
 This can be useful, for example, when one is working with a DNA
sequence from an unknown species.
 Establishing Phylogeny: Using the results received through BLAST,
one can create a phylogenetic tree using the BLAST web-page.

12. Applications of BLAST
 DNA Mapping: When working with a known species, and looking to
sequence a gene at an unknown location, BLAST can compare the
chromosomal position of the sequence of interest, to relevant sequences
in the database.
 Locating Domains: When working with a protein sequence you can
input it into BLAST, to locate known domains within the sequence of
interest.
 Comparison: When working with genes, BLAST can locate common
genes in two related species, and can be used to map annotations from
one organism to another.

13. Thankyou