Big gene
Encyclopedia
The 'big genes' are a class of genes. A big gene
is a single gene whose nuclear
transcript
spans 500 kb or more of chromosomal DNA
.
, which spans 2.3 Mb. Many big genes have modestly sized mRNAs; the exon
s encoding these RNAs typically encompass about 1% of the total chromosomal gene region in which they occur.
structures in big genes.
But because big genes are synthesized very slowly, their synthesis
cannot be completed in rapidly dividing cells. It is in neurons, which do not divide, that a large fraction of the big genes are expressed.
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
is a single gene whose nuclear
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
transcript
Transcript
Transcript may refer to:* Transcript , a copy of a student's permanent academic record* Transcription , the process of creating an equivalent RNA copy of a sequence of DNA* Transcript , a record of all court proceedings...
spans 500 kb or more of chromosomal DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
.
Character
The largest of the big genes is the gene for dystrophinDystrophin
Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophin-associated protein complex...
, which spans 2.3 Mb. Many big genes have modestly sized mRNAs; the exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s encoding these RNAs typically encompass about 1% of the total chromosomal gene region in which they occur.
Synthesis
Full length cDNA sequences are often essential for the delineation of exon/intronIntron
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene. The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final...
structures in big genes.
But because big genes are synthesized very slowly, their synthesis
Synthesis
In general, the noun synthesis refers to a combination of two or more entities that together form something new; alternately, it refers to the creating of something by artificial means...
cannot be completed in rapidly dividing cells. It is in neurons, which do not divide, that a large fraction of the big genes are expressed.