6 a. What is Entrez, and how can it be used to fetch nucleotide sequences and metadata from NCBI 
databases? 

Explanation: Entrez is a suite of tools developed by the National Center for Biotechnology Information 
(NCBI) that allows users to search and retrieve data from various biological databases, including nucleotide 
and protein sequences. Entrez provides programmatic access through the Entrez Programming Utilities (E- 
utilities), which can be used to query databases like GenBank and retrieve sequences, metadata, and other 
related information. 

● Entrez is used for: 

o Searching and retrieving sequence data from the NCBI databases. 

o Fetching sequence metadata such as organism name, gene description, sequence length, 
etc. 

o Accessing biological literature and genome data. 

In Python, the Entrez module from Biopython is used to interact with the NCBI Entrez system. You can 
fetch sequence data by providing an accession number and retrieve metadata such as the sequence's 
description, gene name, organism, and more.