Prokaryotic vs Eukaryotic Genome
The total genetic content of an organism is known as ‘Genome’. It includes both genes and non-encoding sequences of DNA or RNA. For both prokaryotes and eukaryotes, the genetic material in the genome, is the DNA. The sequence, structure, and chemical modification of the DNA expresses the information held within the genome. Not only that, it also enables the genome to replicate, repair and maintain itself. Storage and replication of both genomes are different, but the structure of the DNA remains the same (Double Helix).
Usually prokaryotic organisms have relatively small genomes consisting of one or more DNA molecule. In some prokaryotes, the cells may contain one or more copies of accessory DNA molecules known as ‘plasmids’. The genome and plasmids are often circular in prokaryotes, but there can be exceptions too. Usually plasmids contain some non-essential information in their cells. The genome and plasmids are found in the cytoplasm of the prokaryotic cells.
Eukaryotic genome contains larger and linear DNA molecules packaged with histone proteins into chromosomes. These chromosomes are gathered inside a nucleus enclosed in a nuclear envelope. Apart from that, circular DNA molecules can be found in the mitochondria and chloroplast. These DNA molecules are also considered as a part of prokaryotic genome.
Prokaryotic vs Eukaryotic Genome
• Prokaryotic genome contains only one chromosome, but eukaryotic genome contains multiple chromosomes. Due to this difference, a large part of eukaryotic genome is present inside a nucleus which is the largest organelle in a live cell. There is no such organelle found in prokaryotes so that their genome can be found in the cytoplasm.
• Generally prokaryotic DNA has a circular structure, but there are exceptions. DNA linear strands are present in the eukaryotic cells.
• Unlike the prokaryotic genome, the eukaryotic genome is more complex with longer genes.
• Prokaryotic genome has up to 90% coding sequences while the coding sequence in eukaryotic genome is often around 3%.
• ‘Supercoiling of DNA’ during the cellular cycle does exist in both prokaryotic and eukaryotic genomes, but still, the supercoiling patterns are different. Since the prokaryotes have circular genomes, the domains tend to be pinched off from the loop to form small supercoiled domains.
• One replication site is needed for circular prokaryotic genome. The starting point of replication is known as ‘ori’. Replication starts from this point and proceeds in both direction resulting in very quick division rates in prokaryotes, more than in eukaryotes.
• Non coding DNA ends, also known as telomeres, are present in eukaryotic genome. Telomeres cannot be copied during the replication process. The prokaryotic genome, being circular, has no such end or telomere so that the entire genome can be copied.
• Eukaryotic genome can be either haploid or diploid while prokaryotic genome cannot be haploid as prokaryotes have only one chromosome in their genome.
• Introns are DNA fragments between sections of a real gene. These introns are more common in eukaryotic genome while they are very rare in prokaryotic genome.
• Eukaryotes can have long stretches of two or more repeating nucleotides. Therefore, unlike in eukaryotic genome, repeated sequences are very rare in prokaryotic genome.
• Unlike in the eukaryotic genome, high amount of protein encoding genes are available in the prokaryotic genome.
• Normally eukaryotic genome has hundreds of rRNA genes while prokaryotic genome has 1 to 10 rRNA genes (mean <5).