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This module is an introduction to performing searches of the NCBI databases using Entrez, the NCBI web-based search and retrieval tool for integrated search results from multiple databases.

Entrez (1) is a search and retrieval tool developed by NCBI that is capable of searching multiple NCBI databases with just one query. Entrez returns search results that can include a combination of many types of data on the query, such as nucleotide sequences, protein sequences, macromolecular structures, and related articles in the literature. Prior to the creation of Entrez, an individual might have to place one query to a nucleotide database to find a nucleotide sequence, submit another query to a structural database to find the published structure of the gene product, and submit a final query to a literature database to find citations for journal articles on the query topic. NCBI recognized the time and effort that could be saved by a tool that could cross-link these databases and integrate all information related to a given query subject into one report.View the Entrez Database page . This module contains a few problem questions, for use in a computer lab setting. The lab instructor may require that yousupply answers to these questions as an indication that you have completed the module.

The Entrez Nucleotides database includes sequences from GenBank, RefSeq, and PDB. GenBank is the National Institutes of Health (NIH) genetic sequencedatabase. GenBank, the DNA DataBank of Japan (DDBJ) and the European Molecular Biology Laboratory (EMBL) comprise the International Nucleotide SequenceDatabase Collaboration. These three organizations exchange data on a daily basis. The number of bases in the Entrez Nucleotides database currently growsat an exponential rate. Click on the Nucleotide link listed under the heading "Nucleotide Databases".

What is the number of bases stored in the Entrez nucleotide database, as of the last report?

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Use the back arrow of the browser to return to the Entrez Database web page. Locate the MMDB (Molecular Modeling DataBase), one of NCBI's structure databases and clickon the link to read about it. MMDB is a subset of three-dimensional structures obtained from the ProteinData Bank (PDB), excluding theoretical models. While the protein databases contain protein sequences, the structural database contains coordinate files (PDB files) of biological molecules with solved (known) structures.Click on the arrow next to the search box at the top of the web page and view the list of databases for selection.The literature database is accessed through PubMed, which encompasses the National Library of Medicine'sjournals database, MEDLINE, as well as providing some additional online services. MEDLINE is a collection of medical and life science journalcitations that includes articles dating back to the mid-1960's.Entrez allows access to information such as nucleotide and protein sequencesorganized by species in the NCBI taxonomy database, also found on the selection list. The connectivity of the databases available on the selection list are indicated by the diagram on the Entrez Database web page . Click on the diagram to access a Flash model of Entrez database connectivity. As long as the browser has a Flash plug-in, placing the mouse over one of the nodes representing a database will highlight its connectivity.Try this on the node labeled "Protein". Actually clicking on the node will forward the user to the database home page.

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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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Source:  OpenStax, Bios 533 bioinformatics. OpenStax CNX. Sep 24, 2008 Download for free at http://cnx.org/content/col10152/1.16
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