The biological basis of life: DNA replication

Whether it is in prokaryotes or eukaryotes, the DNA replication takes place before the cells are divided, which helps ensure that the cells have an exact copy of their parent’s genetic material. DNA replication introduces many differences between the process it carries out in prokaryotes and eukaryotes, depending on the size of the molecules and the time consumed in the method. In this section, we will discuss DNA replication in eukaryotes and prokaryotes. Let’s begin with the understanding of DNA replication.

DNA Replication

DNA replication refers to a process wherein the DNA creates an exact copy of itself. The process is taken care of by the DNA polymerase, the enzyme family member. This replication works at the rate of 50 nucleotides per second in mammals, while in bacteria, the rate is approximately 500 nucleotides per second.

Generally, the hydrogen bonds among two bases between two DNA strands break. It leads the strand to unroll. In this process, every strand works as a template for synthesising new strands. Furthermore, the entire process continues until all the nucleotides on the template are with the free nucleotides, and a couple of identical DNA strands have been formed. This whole model of replication is termed the semi-conservative model of replication.

Let us take this topic ahead with a brief on DNA Replication in Prokaryotes and Eukaryotes.

DNA Replication in Prokaryotes

DNA replication in Prokaryotes occurs right before a cell splits into an organism and makes sure both daughter cells get an exact copy of the parent’s genetic material. 

The process works up to the semi-conservative replication model and leads to a DNA with double strands in which one is parental, and the other is the daughter strand. We will now read on the process of prokaryotic DNA replication step by step:

• The process begins at the origin of replication, the DNA molecule
• At a spot on the DNA molecule, the double-helical structure of the DNA is unrolled by enzymes. It allows the replication of access to components
• After that, the helicase enzyme unwinds the helix to create a pair of replication forks
• DNA isomerases and SSB proteins establish the helix that has been uncoiled
• Ten base RNA primers are formed by Primase, which starts the synthesis of the strand that is leading and lagging
• The synthesis goes on in the 5’ to 3’ direction by the DNA Polymerase III
• The lagging strand also undergoes synthesis in the 5’ to 3’ direction. However, the creation of Okazaki fragments discontinues it
• The ten base RNA primers are removed by the DNA polymerase I, and deoxynucleotides bridge the gap
• Then the DNA ligase seizes the breaks between the Okazaki fragments and around the primers to create continuous strands

Note that this process of prokaryotic DNA replication is carried out in the cell cytoplasm.

DNA Replication in Eukaryotes

The eukaryotic DNA replication is carried out in the cell nucleus. Like prokaryotic DNA replication, eukaryotic cells also take a hand from the semi-conservative replication process. Let us understand the process of DNA replication in Eukaryotes with the following steps:

• The process starts at multiple origins in a chromosome wherein the one origin works between 30 and 300 kb of DNA depending on the species and tissues
• At each origin, there is a replication bubble of two forks. The DNA replicated within the control of one source is known as a replicon
• The synthesis process goes on until all bubbles come together
• At the beginning of the process, the DNA unwinds using the help of enzymes which open the door for replication to access components
• The helix that is unwound creates a pair of replication forks, and the DNA topoisomerases and SSB proteins stabilise it
• DNA polymerases make the RNA primers required to carry out the process, and it starts the synthesis of the lagging strands. The leading strand and Okazaki fragments are synthesised by DNA polymerase
• The synthesis in the lagging strand is discontinuous, while in the leading one, it goes on continuously. The process of synthesis in both strands works in the 5′to 3′ direction
• As the process completes, the DNA ligase seizes the breaks between the Okazaki fragments and around the primers to create continuous strands

Difference Between Prokaryotic and Eukaryotic DNA Replication

Conclusion

As the processes discussed above suggests DNA replication in eukaryotes and prokaryotes has both similarities and differences. You also learned that there are factors like molecules, origin, direction, and more contributing to that contrast and commonplace between both. To understand the DNA aspect of biology, it is crucial to grasp your learning over the aspects of DNA replication.