DNA replication


January 19, 2022

DNA replication is the process of making two new DNAs with original DNA, and the DNA polymerase complex plays a role. It occurs once in the process of cell division and has a complex error correction device to reduce mistakes in the replication process. The DNA polymerase responsible for DNA replication makes a base pairing error once in 100,000 times, but the probability of another error occurring by the correction function is reduced to 1 in 100,000. Therefore, a replication error occurs with a probability of 10-5 x 10-5 10-10 (1 in 10 billion). From a molecular biology point of view, DNA replication is the process of producing two identical molecules of DNA from a single DNA molecule. It occurs in all living things and is the basis of biological inheritance. DNA is a double helix structure made up of two complementary strands. During replication, the two DNA strands separate from each other. Each separate strand is the backbone of a process called semi-conservative replication. A set of self-diagnostic mechanisms also exist to ensure replication and accuracy.

Replication Order

The helicase enzyme breaks the hydrogen bonds between the double helix of DNA and releases each strand separately. Unpacked DNA forms a Y-shaped replication fork. - Since each strand is capable of complementary binding, it can be the basis for new DNA molecules. DNA polymerase creates a new helix by creating hydrogen bonds between several complementary nucleotides. DNA replication starts at the origins of replication because a specific site that can be recognized by the DNA polymerase complex exists on the DNA. To prevent the DNA helix from twisting during replication, DNA topoisomerases break up and recombine the DNA helix to release the twist. When DNA polymerase makes new DNA, it can only make it in the 5' to 3' direction. Since the double helix of DNA is originally bound in opposite directions, the direction of attaching new nucleotides is from the 3' direction of the original DNA. Since DNA polymerase cannot attach to single-stranded DNA, it can attach only under the double helix, so RNA primase enzyme attaches an RNA primer to DNA. The DNA polymerase then appends nucleotides to the bottom of it. RNA primers are later replaced with DNA by DNA polymerase. During replication, one strand of DNA is continuously synthesized (leading strand), but the opposite strand is synthesized consecutively at regular intervals (lagging strand). This is because DNA polymerase can make sugar-phosphate bonds only in the 5'-3' direction of the sugar. Broken fragments of newly formed DNA in the lagging strand are called Okazaki fragments. An enzyme called DNA ligase binds the broken pieces together. A hydrogen bond is formed between the base pairs of the newly formed DNA, completing DNA replication.


As DNA replication occurs, the ends are gradually lost. The reason is that if the RNA primer is removed after the DNA is attached to the last RNA primer, the 3'-OH group required for DNA to attach to the site is not present, so that part cannot be replicated. To address this genetic loss, telomeres attach to the back of the DNA, prolonging the lifespan of the cell.


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