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23.1B: Characteristics of Eukaryotic DNA

  • Page ID
    13578
  • Eukaryotes, having probably evolved from prokaryotes, have more complex traits in both cell and DNA organization.

    Learning Objectives

    • Compare and contrast prokaryotic DNA to eukaryotic DNA

    Key Points

    • Prokaryotic genomic DNA is attached to the plasma membrane in the form of a nucleoid, in contrast to eukaryotic DNA, which is located in a nucleus.
    • Eukaryotic DNA is linear, compacted into chromosomes by histones, and has telomeres at each end to protect from deterioration.
    • Prokaryotes contain circular DNA in addition to smaller, transferable DNA plasmids.
    • Eukaryotic cells contain mitochondrial DNA in addition to nuclear DNA.
    • Eukaryotes separate replicated chromosomes by mitosis, using cytoskeletal proteins, whereas prokaryotes divide more simply via binary fission.

    Key Terms

    • telomere: either of the repetitive nucleotide sequences at each end of a eukaryotic chromosome, which protect the chromosome from degradation
    • plasmid: a circle of double-stranded DNA that is separate from the chromosomes, which is found in bacteria and protozoa

    Characteristics of Eukaryotic DNA compared to Prokaryotic DNA

    Prokaryotic cells are known to be much less complex than eukaryotic cells since eukaryotic cells are considered to be present at a later point of evolution. It is probable that eukaryotic cells evolved from prokaryotic cells. Differences in complexity can be seen at the cellular level.

    The single characteristic that is both necessary and sufficient to define an organism as a eukaryote is a nucleus surrounded by a nuclear envelope with nuclear pores. All extant eukaryotes have cells with nuclei; most of a eukaryotic cell’s genetic material is contained within the nucleus. In contrast, prokaryotic DNA is not contained within a nucleus, but rather is attached to the plasma membrane and contained in the form of a nucleoid, an irregularly-shaped region that is not surrounded by a nuclear membrane.

    image

    Cellular location of eukaryotic and prokaryotic DNA: Eukaryotic DNA is stored in a nucleus, whereas prokaryotic DNA is in the cytoplasm in the form of a nucleoid.

    Eukaryotic DNA is packed into bundles of chromosomes, each consisting of a linear DNA molecule coiled around basic (alkaline) proteins called histones, which wind the DNA into a more compact form. Prokaryotic DNA is found in circular, non-chromosomal form. In addition, prokaryotes have plasmids, which are smaller pieces of circular DNA that can replicate separately from prokaryotic genomic DNA. Because of the linear nature of eukaryotic DNA, repeating non-coding DNA sequences called telomeres are present on either end of the chromosomes as protection from deterioration.

    Mitosis, a process of nuclear division wherein replicated chromosomes are divided and separated using elements of the cytoskeleton, is universally present in eukaryotes. The cytoskeleton contains structural and motility components called actin microfilaments and microtubules. All extant eukaryotes have these cytoskeletal elements. Prokaryotes on the other hand undergo binary fission in a process where the DNA is replicated, then separates to two poles of the cell, and, finally, the cell fully divides.

    A major DNA difference between eukaryotes and prokaryotes is the presence of mitochondrial DNA (mtDNA) in eukaryotes. Because eukaryotes have mitochondria and prokaryotes do not, eukaryotic cells contain mitochondrial DNA in addition to DNA contained in the nucleus and ribosomes. The mtDNA is composed of significantly fewer base pairs than nuclear DNA and encodes only a few dozen genes, depending on the organism.