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The upcoming discussion will update you about the difference between prokaryotic chromosome and eukaryotic chromosome.
Difference # Prokaryotic (Bacterial) Chromosome:
1. Structural organization of bacterial chromosome is simple and is represented mainly by double-stranded DNA molecule. Although there are specific proteins associated with bacterial chromosome (not the histories) that help stabilize its supercoiled domains. Compared to eukaryotic chromosome, one can consider bacterial chromosome to be naked DNA.
2. Bacterial chromosome is covalently closed circular structure consisting of only a single molecule of DNA (with few exceptions such as Borellia burgdorfii and Streptomyces the chromosomes of which are linear).
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3. Only one bacterial chromosome occurs per bacterial cell (with few exceptions such as Rhodobacter sphaeroides, a gram-negative phototroph that possesses 2 chromosomes per cell).
4. Bacterial chromosome contains only a single copy of each gene and is therefore genetically haploid.
5. Bacterial chromosomes are shorter and contain lesser number of genes.
6. Bacterial chromosome lies free in the cell cytoplasm without any membrane to separate the chromosome from the cytoplasm., Since the ribosomes also occur free in cell cytoplasm, the process of transcription and translation are not spatially separated.
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7. Except few, the bacterial DNAs do not contain introns, the noncoding sequences. As a result, the protein coding genes are not interrupted by introns and synthesize a single mRNA often containing more than one coding region. Each coding region independently synthesizes one or more proteins depending upon the number of operons (Fig. 5.37).
Difference # Eukaryotic Chromosome:
1. Structural organization of eukaryotic chromosome is complex as it contains more than just DNA. In addition to DNA large amount of histone proteins wound around DNA molecule in a very regular fashion to form structures called nucleosome. The nucleosomes aggregate to form a fibres material called chromatin, which itself further compact by folding and looping to eventually form very dense structure called chromosome.
2. Each eukaryotic chromosome is linear and consists of several pieces of DNA.
3. Eukaryotic chromosomes are more than one per cell, and this number varies with the organism. For example, Saccharomyces cerevisiae, a single-called Baker’s yeast, contains 16 chromosomes arranged in eight pairs, while human cells contain 46 chromosomes arranged in 23 pairs.
4. Eukaryotic chromosome typically contains 2 copies of each gene and is therefore genetically diploid. The diploid eukaryotic genome is halved to haploid via the process called meiosis.
5. Eukaryotic chromosomes are larger and contain greater number of genes.
6. Eukaryotic chromosome occurs in the cell nucleus, which is surrounded by nuclear membrane that separates chromosome from the cytoplasm while the ribosomes are in the cytoplasm, the processes of transaction and translation are spatially separated.
7. Eukaryotic chromosome contains both introns (noncoding sequence) and exons (coding sequence). As a result, the protein coding genes are interrupted by introns. Both introns and exons are transcribed into the primary RNA transcript from which the nature (functional) mRNA is formed by excision of introns and transported to the cytoplasm for translation (protein synthesis) (Fig. 5.38).
