What are the 3 steps of DNA replication?

Introduction:

Definition: 

The process by which the DNA double helix forms exactly another molecule is called DNA replication. Watson and Crick's explanation of the mechanism of DNA replication based on their DNA structure has been later proven correct by various scientists' radiological experiments.

Where and when does DNA replication take place:

DNA replication takes place in the nucleus during interphase in eukaryotic cells and in the cytoplasm of prokaryotic cells.

Type Of DNA Replication Process:

Transcription is usually done in three types of processes.

Conservative:

One of the two DNA strands created is old and the other two strands are new.

Semiconservative:

The two strands of DNA created both have one strand old and the other strand new.

Dispersive:

The two DNAs created both have old and new parts in place.

Required Ingredients:

1. Mold 2. Replication complex (helicase, polymerase, primase, DNAse) 3. Strength 4. free nucleotides

DNA Replication Mechanism / Process:

1. The specific place in DNA where replication starts is called the origin or origin.

2. At the start of transcription, the helicase enzyme breaks the hydrogen bonds between the double-stranded DNA from the Auri portion. As a result, it becomes a formula.

DNA Replication

3. SSBP (Single Strand Binding Protein) is then attached to each strand, preventing the strands from rejoining. A Y-shaped replication fork is formed in the DNA as the two strands diverge.

4. Each different element acts as a mold for its complement.

5. Based on the template, the enzyme primase adds 2-100 nucleotides to form small RNA fragments, called primers.

6. DNA polymerase only adds nucleotides at the 3ʹ end, so new strands always grow in the 5ʹ → 3ʹ direction. Which nucleotide is added after which depends on the template? For example: If the base sequence of the mold is ATTGCCG, the sequence in the new formula will be TAACGGC.

7. A new strand that complements a mold strand grows intermittently or continuously, called the leading strand. The other new formula grows slowly or piecemeal. This is called Lagging Strand.

8. Each segment of the lagging strand is called an Okazaki Fragment. The enzyme ligase joins the Okazaki fragments. When replication is complete, the replication complex dissociates.

* In this way two DNA molecules are created from one DNA as before. The two strands of DNA created both have one strand old and the other strand new. That is why it is called a semiconservative process.

Enzyme Function in DNA Replication:

DNA replication is a process that is heavily dependent on enzymes. Numerous enzymes, such as DNA-dependent DNA polymerase, helicase, ligase, and others, are involved in DNA replication.  The primary enzyme among them is DNA-dependent DNA polymerase.

Prokaryotic DNA Replication Process:

• Prokaryotes replicate their DNA in the following locations:
• At the start of replication, the two DNA strands unwind.
• Replication forks are created after the DNA is opened by helicase.
• Around the replication fork, the single-strand binding proteins coat the DNA to stop DNA rewinding.
• Topoisomerase stops DNA from supercoiling.
• Primase synthesizes NA primers. The DNA strand and these primers complement each other.
• The primers' ends are where DNA polymerase III begins to assemble nucleotides.
• The lagging and leading strands are still growing longer.
•  The gaps are filled with DNA Polymerase I, sealed by ligase, and the primers are removed.

Eukaryotic DNA Replication:

• Eukaryotic DNA replication is comparable to prokaryotic DNA replication.
• Eukaryotes, as opposed to prokaryotes, have a more complicated initiation process. 
• Multiple replication origins are present in eukaryotes. 
• Other initiator proteins form a pre-replication complex. 
• Although the enzymes used are different, the process is exactly the same. 
• For instance, the enzyme Pol performs the polymerization process in eukaryotes, whereas DNA Pol III does so in prokaryotes.

Conclusion:

DNA replication begins at multiple points on eukaryotic chromosomes, so replication forks converge and terminate at multiple points. Since eukaryotes have linear chromosomes, DNA replication cannot reach the very ends of the chromosomes. This problem causes DNA to be lost from the end of the chromosome between each replication cycle. Telomeres are regions near the ends of repetitive DNA and help prevent gene loss due to shortening. Shortening of telomeres is a normal process in body cells. It shortens the telomeres of the aberrant DNA chromosomes. As a result cells can divide only a certain number of times before DNA damage prevents further division (known as the Hayflick limit). In this germline cell line that transfers DNA to the next generation, telomerase extends repetitive sequences in the telomere region to prevent telomerase loss. Telomerase can become incorrectly activated in body cells, sometimes leading to the formation of cancer. Increased telomerase activity is one of the hallmarks of cancer.