The Replication process in eukaryotic and prokaryotic cells is quite similar. Almost the same enzymes are involved. 1)eukaryotic, 2)multiple, 3)circular.
<h3>What is the prokaryotic DNA replication process?</h3>
In prokaryotic cells, DNA Replication consists of the unwinding and opening of the double-stranded DNA molecule, a process that starts at the replication origin.
The process is completed in three stages,
⇒ Initiation, in which helicase and topoisomerase are the first enzymes involved.
Helicase works in the replication origin.
- It separates the DNA into two strands allowing the replication fork to advance by unwinding the DNA.
- It breaks hydrogen bonds between nitrogenated bases pairs.
Topoisomerase impedes the DNA double helix near the replication forks to get too coiled when the DNA is opening.
⇒ Elongation, in which DNA polymerase I and III, primase, and ligase act,
Polymerase I and III are responsible for DNA elongation.
- They are in charge of adding nucleotides to the growing chain, from 3' to 5' extremes.
- It includes only nucleotides that complement the original strand.
- They need to recognize a primer to begin.
- The new chain grows in 5’-3’ direction
Primase is in charge of synthesizing primers.
DNA polymerase I eliminate ARN primers and substitute them with DNA.
DNA ligase seals the gaps that remain after replacing the primers.
⇒ Mistakes correction
Endonuclease cuts the wrong segment
Polymerase I and III are in charge of correcting errors and filling empty spaces.
Ligase seals the corrected extremes.
The prokaryotic replication result is two DNA molecules, each of them carrying an old strand and a new strand.
<h3>
What is the eukaryotic DNA replication process?</h3>
Eukaryotic DNA replication is the process through which DNI molecule duplicates. This event takes place during the S stage of the interphase. So when the cell divides during mitosis or meiosis, each cell will get a complete set of chromosomes.
DNI replication is semi-conservative because each new molecule carries an original DNI strand and a new one. The fact that the new molecule is composed of an original strand makes it semi-conservative. The old existing strands are used to synthesize the new complementary strand.
The main difference concerning the prokaryotic replication process is that in eukaryotic cells there are
- 5 different polymerase enzymes
- several replication origins per chromosome
- involves histones
The origin of the replication requires
- The helicase enzyme breaks hydrogen bonds and separates the two original strands.
- The topoisomerase enzyme is necessary to release tension.
- Other proteins are also needed to join the strains and keep them separated.
Once the molecule is opened, there is a region named replication forks.
- DNA polymerase makes the new nucleotides enter the fork and pairs them with the corresponding nucleotide of the original strand. Adenine pairs thymine, and cytosine pairs guanine.
DNA strands are antiparallel, and replication occurs only in 5'-3'direction. So one of the strands will replicate continuously, while the other strain will be formed by short fragments known as Okazaki fragments.
Primers are needed to make the DNA polymerase work. Primers are small units of RNA and are placed at the beginning of each new fragment. These are later eliminated by Polymerase.
Ligase seals the gaps.
<u>Complete sentenses</u>
Before a cell divides, its DNA must be replicated without errors so that the genetic codes for proteins are expressed properly. In<u> </u><u>eukaryotic</u><u> </u>cells, which have linear chromosomes, replication occurs in<u> </u><u> multiple </u>locations and ends when all the chromosomes are copied. In prokaryotic cells, which have<u> </u><u>circular </u>DNA, replication starts in only a single location and proceeds until the entire chromosome is copied.
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