Key Differences in Process Enzymes and Origin of Replication in Prokaryotes and Eukaryotes
DNA replication is a process in which the genetic material of a cell, in this case, the DNA makes an exact copy of itself and the process is controlled by the enzyme DNA polymerase. In mammals, the rate of replication is around 50 nucleotides per second whereas, in bacteria, the rate is around 500 nucleotides per second.
In general, the hydrogen bonds between two complementary bases between two DNA strands break which helps the strand to unwind. Each strand acts as a template for synthesis of a new strand which is complementary to itself.
The entire process continues till all the nucleotides on the template have joined with the free nucleotides and two identical DNA strands are formed. This model of replication is known as the semiconservative model of replication.
In this topic, we will have a brief overview of both eukaryotic and prokaryotic replication and what their differences are.
DNA Replication in Prokaryotes
Centring on the general principle of DNA replication, the prokaryotic DNA replication in prokaryotic cells takes place just before a cell divides in an organism and ensures both daughter cells receive an exact copy of the parent’s genetic material. The process uses the semiconservative model of replication which results in a double-stranded DNA with one parental and one daughter strand.
The Steps of Prokaryotic DNA Replication are as follows:
The DNA replication process is bi-directional begins at a spot on the DNA molecule called the origin of replication.
At this spot, enzymes unwind the double helix structure of the DNA which makes its components accessible for replication.
The helix is unwound by the helicase enzyme to form a pair of replication forks, and the unwound helix is stabilised by SSB proteins and DNA isomerases.
Primase forms 10 base RNA primers which initiate the synthesis of the leading and the lagging strand.
The leading continues to synthesise in the 5’ to 3’ direction by DNAP III (DNA Polymerase III)
The lagging strand is also synthesised in the 5’ to 3’ direction but it is discontinued through the formation of Okazaki fragments.
DNA polymerase I removes the 10 base RNA primers and replaces the gap with deoxynucleotides.
Then DNA ligase seals the breaks between Okazaki fragments as well as around the primers to form continuous strands.
The entire process of replication takes place in the cell cytoplasm.
DNA Replication in Eukaryotes
The eukaryotic DNA replication takes place in the cell nucleus and only occurs in the S phase at many chromosomal origins. Similar to prokaryotic DNA replication, eukaryotic cells also use the semi-conservative process of replication but there are multiple origins of replication.
The Steps of the Eukaryotic DNA Replication are as follow:
The replication process starts in a chromosome at multiple origins, with one origin being at 30-300 kb of DNA depending on the tissue and species.
A replication bubble of two forks forms at each origin. The DNA replicated under the control of a single origin is called a replicon. The synthesis proceeds until all bubbles merge together.
The process starts with the unwinding of DNA with the help of enzymes, which makes its components accessible for replication.
The unwound helix forms a pair of replication forks and is stabilised by DNA topoisomerases and SSB proteins.
The RNA primers required for the process are made by DNA polymerases α which initiates the synthesis of the lagging strand and makes the first primer. It then extends it with a short region of DNA.
The Okazaki fragments and the leading strand are synthesised by DNA polymerase δ.
The leading strand is synthesised continuously whilst the lagging strand is synthesised discontinuously. Both strands are synthesised in the 5′to 3′ direction.
At completion, DNA ligase seals the breaks around the primers and between the Okazaki fragments.
Although there are some similarities between DNA replication in prokaryotes and eukaryotes, the differences are many. Here we will discuss the differences between prokaryotes’ and eukaryotes’ DNA replication process.
Difference Between Prokaryotic and Eukaryotic Replication: Tabular Form
FAQs on Difference Between Prokaryotic and Eukaryotic DNA Replication Explained
1. What is the difference between prokaryotic and eukaryotic DNA replication?
The main difference between prokaryotic and eukaryotic DNA replication lies in their origin sites, speed, enzymes, and cellular location.
- Prokaryotic DNA replication occurs in the cytoplasm and starts from a single origin of replication (OriC).
- Eukaryotic DNA replication occurs inside the nucleus and begins at multiple origins of replication on each chromosome.
- Prokaryotes replicate circular DNA, while eukaryotes replicate linear chromosomes.
- Eukaryotic replication is slower but more complex due to larger genome size.
2. Where does DNA replication occur in prokaryotic and eukaryotic cells?
DNA replication occurs in the cytoplasm of prokaryotic cells and in the nucleus of eukaryotic cells.
- Prokaryotes lack a membrane-bound nucleus, so replication happens in the nucleoid region.
- Eukaryotes have a true nucleus where replication of linear chromosomes takes place during the S phase of the cell cycle.
3. How many origins of replication are present in prokaryotes and eukaryotes?
Prokaryotes usually have a single origin of replication, while eukaryotes have multiple origins on each chromosome.
- In prokaryotes like Escherichia coli, replication begins at one site called OriC.
- Eukaryotic chromosomes contain many origins to ensure timely replication of large genomes.
4. What enzymes are involved in prokaryotic vs eukaryotic DNA replication?
Both systems use similar core enzymes, but the specific DNA polymerases differ between prokaryotes and eukaryotes.
- In prokaryotes, DNA polymerase III is the main replication enzyme, and DNA polymerase I removes RNA primers.
- In eukaryotes, DNA polymerase α, δ, and ε carry out replication.
- Both use helicase, primase, and DNA ligase.
5. Why is eukaryotic DNA replication more complex than prokaryotic replication?
Eukaryotic DNA replication is more complex because eukaryotes have larger, linear genomes organized with histone proteins.
- DNA is wrapped around histones forming chromatin.
- Replication involves multiple origins and coordinated control during the cell cycle.
- Special mechanisms like telomere replication are required for linear chromosomes.
6. How does the speed of DNA replication differ in prokaryotes and eukaryotes?
Prokaryotic DNA replication is faster than eukaryotic replication.
- In prokaryotes, replication occurs at about 1000 nucleotides per second.
- In eukaryotes, replication proceeds at about 50–100 nucleotides per second.
- Eukaryotes compensate for slower speed by using multiple origins of replication.
7. What is the structure of DNA being replicated in prokaryotes and eukaryotes?
Prokaryotes replicate circular DNA, while eukaryotes replicate linear DNA molecules.
- Prokaryotic chromosomes are usually single and circular.
- Eukaryotic chromosomes are multiple and linear.
- Linear chromosomes require telomeres to protect chromosome ends.
8. What is the role of telomerase in eukaryotic DNA replication?
The enzyme telomerase extends telomeres to prevent chromosome shortening during eukaryotic DNA replication.
- It adds repetitive DNA sequences to the ends of linear chromosomes.
- This solves the end-replication problem.
- Telomerase is active in germ cells, stem cells, and many cancer cells.
9. Are the steps of DNA replication the same in prokaryotes and eukaryotes?
The basic steps of DNA replication—initiation, elongation, and termination—are the same in both prokaryotes and eukaryotes.
- Initiation begins at origins of replication.
- Elongation involves synthesis of leading and lagging strands.
- Termination completes replication.
- However, regulatory mechanisms and proteins involved differ between the two groups.
10. What are Okazaki fragments and how do they differ in prokaryotic and eukaryotic replication?
Okazaki fragments are short DNA segments synthesized discontinuously on the lagging strand during DNA replication.
- In prokaryotes, Okazaki fragments are longer (about 1000–2000 nucleotides).
- In eukaryotes, they are shorter (about 100–200 nucleotides).
- They are later joined by DNA ligase to form a continuous strand.
