Finding Sequence Data on Ensembl & NCBI: Accession Numbers

Eukaryotic genes are discontinuous (mosaic) and consist of alternating exons and introns. Exons are coding sequences retained in mature mRNA and translated into protein, while introns are non-coding sequences removed during splicing. The ovalbumin gene contains 8 exons and 7 introns, with approximately 7700 base pairs total (three-quarters introns). Alternative splicing allows a single pre-mRNA to produce multiple mature mRNAs with different exon combinations, generating multiple protein isoforms from a single gene. This greatly increases proteome complexity, as most human genes undergo alternative splicing. The definition of a gene in eukaryotes must account for this complexity: a gene is a DNA sequence transcribed into a single RNA molecule that can undergo alternative splicing to produce multiple mature RNAs.

Eukaryotic genes contain coding regions called exons (black) and non-coding regions called introns (blue). RNA splicing removes introns and joins exons to form mature mRNA. Alternative splicing allows a single gene to produce multiple mRNA transcripts by including different combinations of exons. For example, a gene with three exons can produce three different mRNA combinations: exons 1-2-3, exons 1-3, and exons 2-3. This process enables one gene to generate multiple protein variants, solving the discrepancy between gene number (30,000) and protein requirement (45,000) in humans.

A gene is a specific sequence of DNA nucleotides containing instructions for making a protein. A gene contains functional regions: a promoter (start signal for transcription), a terminator (end signal), exons (coding regions translated into protein), and introns (non-coding regions removed during RNA processing). Eukaryotic genes contain both coding and non-coding regions, while prokaryotic genes typically lack introns. The promoter signals where RNA polymerase binds to begin transcription, and the terminator signals where transcription should end.

A gene includes the promoter (where transcription begins), coding region (exons and introns), and terminator sequence. The coding region extends from the start codon (AUG) to the stop codon. UTR (Untranslated Region) sequences flank the coding region and are transcribed but not translated. Alternative splicing allows different combinations of exons from the same pre-mRNA to be joined, producing different mature mRNAs and proteins from a single gene. This is only possible in eukaryotes because they have introns and spliceosome machinery. Euchromatin is less condensed and transcriptionally active, while heterochromatin is highly condensed and transcriptionally inactive. Heterochromatin maintains chromosome structure at centromeres and telomeres and regulates gene expression by keeping certain genes permanently silenced.

This section explains the discovery that genes are not continuous DNA sequences but are split into exons (coding regions) and introns (non-coding regions). Splicing enzymes remove introns and join exons to create functional mRNA. Alternative splicing allows the same gene to produce different proteins by including or excluding different exons - from one gene, multiple protein variants can be produced. This challenged the traditional 'one gene, one protein' model. Different tissues can use different splicing patterns for the same gene, producing different protein variants in different body parts. This dramatically increases the complexity of the genome and explains how a single genome can produce diverse cell types.

Biological databases are organized repositories of biological information. Different databases serve different purposes: (1) Genomic databases store DNA sequences; (2) Transcriptomic databases store RNA sequences; (3) Transcription factor binding motif databases store information about DNA sequences that transcription factors bind to; (4) Protein domain databases store information about functional units in proteins; (5) Protein sequence databases store amino acid sequences from various organisms.

Biological databases are information storehouses that store and communicate large biological data sets. They are essential because of the enormous growth of sequencing data and structural data in biology. These databases provide storage, retrieval, and data mining provisions for scientists to access and generate useful information. The data must be made available to scientists free of cost for research and development.

The main purpose of biological databases is to store and manage biological data and information in computer-readable forms. The types of information stored include: biological sequences, structures, binding sites, metabolic interactions, molecular actions, functional relationships, protein families, motifs, and homologous sequences. This data is required to answer many questions that biologists want computational biologists to address.

Biological databases are specialized digital libraries that organize massive amounts of biological information including DNA sequences, protein functions, and molecular structures. They serve as repositories where scientists from anywhere in the world can quickly find and access specific biological information. These databases are crucial because without proper organization, biological data would be like a treasure hidden in a million unlabeled boxes, serving no practical purpose.

Biological databases are electronic systems for organizing and storing specialized data. They include nucleotide sequence databases containing genes and genomes, protein databases storing amino acid sequences, structural databases providing 3D molecular topology, and databases for protein-protein interactions, metabolic pathways, gene expression profiling, and scientific literature. These databases support essential operations: data input (feeding) and data output (extraction). As experimental research increases, the volume of biological data grows daily, requiring robust systems to manage diverse data types including nucleotide sequences, protein sequences, macromolecule structures, and interaction data efficiently.

Accurate gene nomenclature is critical for proper scientific communication, as unlike objects like roses, genes without standardized names create significant confusion in biomedical literature. General requirements include uniqueness within species, symbol lengths of three to ten characters, and names reflecting gene function. The organizational framework involves the HUGO Gene Nomenclature Committee (HGNC) determining human gene names, with MGI handling mice and RGD managing rats. Names propagate between species based on orthology relationships, with human nomenclature serving as the vertebrate standard. When nomenclature changes occur for gene families, committees collaborate and consult the research community to establish optimal solutions.

Standardized nomenclature guidelines: DNA uppercase, RNA lowercase, proteins use three-letter codes. Common prefixes: cDNA, gDNA, mt, mi, ds, m, tRNA, rRNA, siRNA, snRNA, ncRNA. HUGO Gene Committee uses italics for genes, normal font for proteins, superscripts (+) for wild-type, (-) for mutated. HGVS provides international standards for describing alterations: substitutions (c.1799T>A), nonsense (*), duplications (dup), deletions (del), insertions (ins), inversions (inv), conversions (con), frame shifts (fs). Mutations can be described by DNA position, protein position, or gene/protein name.

Accurate gene nomenclature is essential for proper communication in biomedical research. Unlike objects whose identity isn't affected by different names, genes require precise naming because identification data isn't always available. Confusing gene symbols cause significant problems, especially with automated literature searches. General requirements include uniqueness within species, 3-10 character symbols reflecting gene function, and consistency within gene families. The HUGO Gene Nomenclature Committee (HGNC) determines official human gene names, serving as the model for vertebrate species. Gene nomenclature typically flows from human to mouse and rat through HGNC, MGI, and RGD committees, though discovery order may reverse this flow. For rat genes, naming follows a hierarchy: use human ortholog names with initial capitalization, then mouse orthologs, then functional names, and finally generic ID numbers when no data exists.

Mutation nomenclature follows standardized conventions where variants are described at the DNA level using coding DNA sequences (CDS) with specific prefixes: C for coding DNA, G for genomic, M for mitochondrial, R for RNA, and P for protein sequences; gene symbols must follow HUGO Gene Nomenclature Committee (HGNC) standards, and reference sequences should be identified by accession and version numbers from databases.

The Human Genome Nomenclature Committee (HGNC) is responsible for assigning official symbols and full names to human genes. For FoxP2, the official symbol is FoxP2 and the official full name is Forkhead box P2. This standardized nomenclature system ensures consistency in gene identification across scientific literature and databases. The HGNC provides primary source links back to gene sequences and maintains records of gene aliases that have been used historically for the same gene.