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DA5. DNA Replication in Eukaryotes and Prokaryotes

Statement

In your assigned readings, you learned DNA is used as a template to synthesize new DNA. This process is referred to as replication. Discuss the similarities and differences in DNA replication between eukaryotes and prokaryotes. Are the changes in eukaryotes adaptations? Explain.

Solution

Eukaryotes cell structure is more complex than prokaryotes, and this complexity is reflected on the DNA replication process. This text will discuss the similarities and differences between the DNA replication in eukaryotes and prokaryotes.

Areas of comparison include:

  • DNA structure.
  • DNA replication model: There were three models suggested for DNA replication: conservative, semi-conservative, and dispersive according to the relationship between the parental DNA and the newly formed daughter strands.
  • DNA Polymerases: A group of enzymes that are responsible in adding new nucleotides to the growing DNA strand, there are multiple types in the group and each has specific role and characteristics.
  • Origin of replication: The site where the DNA replication starts, there might be multiple replication process at each single strand, each starts at a different position called the origin of replication.

ProKaryotes

Most prokaryotes contain a single, circular chromosome that is found in an area of the cytoplasm called the Nucleoid (Rye et al., 2016, p. 371). The DNA is twisted by what is known as supercoiling, that is, a turn or more is generated on every 10 base pairs (Rye et al., 2016, p. 372).

The DNA replication mode is semi-conservative, that is, that each of the two parental DNA strands act as a template for new DNA to be synthesized; after replication, each double-stranded DNA includes one parental or “old” strand and one “new” strand.

In prokaryotes, three main types of polymerases are known: `DNA pol I, DNA pol II, and DNA pol III``. It is now known that DNA pol III is the enzyme required for DNA synthesis; DNA pol I and DNA pol II are primarily required for repair functions (Rye et al., 2016, p. 375).

There is a single origin of replication in prokaryotes, and this origin of replication is recognized by certain proteins that bind to this site (Rye et al., 2016, p. 376).

Rate of replication is approximately 1,000 nucleotides per second.

Eukaryotes

Eukaryotic genomes are much more complex and larger in size than prokaryotic genomes (Rye et al., 2016, p. 379), and DNA is wrapped around proteins known as histones to form structures called Nucleosomes (Rye et al., 2016, p. 372).

The DNA replication mode is semi-conservative (Khan Academy, n.d.).

The number of DNA polymerases in eukaryotes is much more than prokaryotes: 14 are known, of which five are known to have major roles during replication and have been well studied. They are known as pol α, pol β, pol γ, pol δ, and pol ε.

There are multiple origins of replication on the eukaryotic chromosome; humans can have up to 100,000 origins of replication per DNA strand.

The rate of replication is approximately 100 nucleotides per second, much slower than prokaryotic replication.

The chromatin (the complex between DNA and proteins) may undergo some chemical modifications, so that the DNA may be able to slide off the proteins or be accessible to the enzymes of the DNA replication machinery (Rye et al., 2016, p. 379) which is a step that is not required in prokaryotes.

The ends of the linear chromosomes are known as telomeres, which have repetitive sequences that code for no particular gene. Telomeres indicates the end of chromosome and protect the coding regions of the chromosome from being lost during replication (Rye et al., 2016, p. 380).

Conclusion

The nucleuses protects eukaryotes’ DNA, and replication process happens separately from any RNA or Protein synthesis and happens in a slower rate compared to prokaryotes; which may interpret why prokaryotes have -usually- more chance of mutations than eukaryotes, and they evolve faster.

References