You have around 30 trillion cells in your body, and DNA is found in most but not all of them. For example, mature red blood cells don't have any DNA.
The DNA isn't just floating around in the cell. Most of it is stored in a small compartment in the cell called the nucleus.
DNA is packed in the chromosome. it is the cell’s hereditary material and contains instructions for development, growth and reproduction.
DNA is a self-replicating structure. replication needs to occur because existing cells divide to produce new cells and Each cell needs a full instruction manual to operate properly. So the DNA needs to be copied before cell division.
NA is made of two linked strands that wind around each other to resemble a twisted ladder ,a shape known as a double helix. Each strand has a backbone made of alternating sugar and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T). The two strands are connected by chemical bonds between the bases: adenine bonds with thymine, and cytosine bonds with guanine.
DNA replication is catalyzed by a set of enzymes. Let’s learn about the DNA replication process and the role of enzymes involved in DNA replication.
1. Replication begins with the spotting of origin of replication, followed of unwinding of two DNA strands.
2. Unzipping of DNA strands needs high energy input hence it catalyzed by enzyme helicase.
3. The separation of two single strands of DNA creates a y shaped called replication fork. The two separated strands will acts as template for making a new strands of DNA
4. An enzymes called primase bind at end of the strand and construct RNA primer by adding RNA nucleotides from 5’ to 3’ direction.
5. DNA polymerase recognize the primer and binds the strands and walks along it, adding new complimentary nucleotides bases to the strand of DNA in 5’ to 3’ direction
6. DNA polymerase are always polymerized from 5’ to 3’ direction. Replication in one of the DNA template forming leading strand towards replication fork from 5’ to 3’ direction, this type of replication is known as continuous replication.
Other DNA template are anti parallel so replication occur away from replication fork, forming lagging strand, this type of replication is known as discontinuous replication.
7. Numerous RNA primers are made by primase enzyme and binds various point along the lagging strand.
8. DNA polymerase recognize the primer and adding new complimentary nucleotide bases to the strand of DNA at 5’ to 3’ direction. This chunks of DNA are known as okazaki fragments.
9. Once all of DNA bases are matched up another enzyme exonuclease strip away the primers.
10. The gaps are filled by polymerase by adding new complimentary bases.
11. Finally, another enzyme called DNA ligase sealed up the strands of DNA into two continuous double strands.
12. The result of DNA replication is two DNA molecules consisting of one new and one old chain of nucleotides. This is why DNA replication is described as semi-conservative, half of the chain is part of the original DNA molecule, half is new.
13. Following replication, the new DNA automatically winds up into a double helix.
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