What is the Genomic DNA?
Genomic DNA holds all of an organism’s genetic information. Almost all organisms genomes are made of DNA. The only ones that aren’t are some viruses, which have RNA genomes. Most species chromosomes include vast amounts of genomic DNA structured into DNA protein complexes. The genomic DNA of different organisms differs in size, number of chromosomes, and nature. DNA genomes found in viruses are often quite tiny and can either be single or double-stranded, linear, or circular in structure. The genomes of all other types of creatures are composed of two strands of DNA. Bacteria only have one chromosome, which is round in shape.
Most of the genomic DNA in eukaryotes is found in the nucleus as several different-sized linear chromosomes. Genomic DNA is also found in the mitochondria and, in plants and lower eukaryotes, and in the chloroplasts. Most of the time, this DNA is a circular molecule, and there are many copies of it in these organelles.
Figure 1: What is genomic DNA? Human cells can fit 6 feet of genomic DNA into a nucleus that is only a few micrometers across by wrapping it around protein beads first. These groups of protein and DNA are called nucleosomes, and they are packed together even more to make chromatin.
Genes are distinct areas within genomic DNA that encode a protein or RNA. A gene is made up of not just the coding DNA sequence but also the regulatory elements that are connected with it and are responsible for controlling gene expression. In addition, nuclear eukaryotic genes have noncoding sequences that are referred to as introns. The number of genes varies greatly between organisms. Coding DNA accounts for only a small portion of eukaryotic genomic DNA; the majority of the DNA is noncoding, with many repetitive sequences.
Although some of the noncoding DNA in a cell has regulatory and structural functions, the majority of this DNA’s role in the cell is still mostly mysterious. Ploidy, or the number of copies of each genetic locus present in a cell, differs between organisms. Although most sexually reproducing animals have two sets of homologous chromosomes in their somatic (body) cells, the reproductive germ cells are haploid and only contain one copy of each chromosome.