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Difference Between Leading DNA Strands and Lagging DNA Strands

Leading DNA Strands and Lagging DNA Strands

For living organisms, the basis of life is to pass on their genetic characteristics to the next generation. This transmission of characteristics is achieved by DNA present in the chromosomes of each living thing. DNA is responsible for the transmission of all hereditary characteristics to the next generation by means of replicating and making two exact copies of its original self.

DNA stands for deoxyribonucleic acid. It is a chromosome’s main constituent. DNA is responsible for all the hereditary characteristics of a person and the transmission of those characteristics to the offspring from their parents. The DNA molecule has two polynucleotide chains; they are in the form of a helix and contain sugar deoxyribose and phosphates which are linked by hydrogen bonds. These hydrogen bonds are between complementary thymine and bases of adenine, guanine, and cytosine. DNA is self-replicating.

DNA replication
DNA replication is a biological process which is necessary for the inheritance of characteristics. It is the process by which the DNA is copied; the double-stranded molecule replicates to produce two identical copies of the molecule. Each strand of DNA molecule acts as a template for the complementary strand to be produced. The DNA splits forming a “fork.” A new DNA strand is always synthesized in a 5’ to 3’ manner, thus the replication of both the strands goes two different ways.

Leading strand
A leading strand is the strand which is synthesized in the 5’-3’direction or the direction the same as the replication fork movement. It is synthesized continuously; there are no breaks in-between. This strand is formed as nucleotides are continuously added to the 3’ end of the strand after polymerase reads the original DNA template.

Lagging strand
A lagging strand is the strand which is synthesized in the 3’-5’ direction or opposite direction as to the movement of the replication fork. It grows or is synthesized away from the fork. Its movement in the opposite direction is the cause why it is discontinuous; it is synthesized in fragments. The primase, which is responsible for adding an RNA primer, has to wait for the fork to open before putting in the primer. The lagging strands have fragments of DNA which are called Okazaki fragments.

The continual synthesis of the lagging strands is prevented by the original DNA orientation; this is the reason why the synthesis of the lagging strand is more complicated than the leading strand.


1.A leading strand is the strand which is synthesized in the 5’-3’direction while a lagging strand is the strand which is synthesized in the 3’-5’ direction.
2.The leading strand is synthesized continuously while a lagging strand is synthesized in fragments which are called Okazaki fragments.
3.Leading strand synthesis does not require an RNA primer while a lagging strand synthesis requires RNA primase.


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  1. Very detailed

  2. No. This is INCORRECT, DNA Polymerase ALWAYS synthesizes in the 5 to 3′ direction. The lagging strand is synthesized in pieces building from 5 to 3′, once helicase opens up more DNA it goes backwards to sit on the newly exposed DNA then once again moves in the 5′ to 3′ direction.

  3. Incorrect!
    RNA primers are necessary for DNA replication in BOTH strands!
    The difference being that the lagging strand needs multiple of them (which leads to the formation of Okazaki fragments) while leading strand synthesis is continuous (only needs one primer).
    The reason it needs multiple is because DNA polimerases can only sinthesize DNA 5’->3’ and adding multiple primers allows for this to happen in the lagging strand.
    However, at the beggining of synthesis in the leading strand A PRIMER IS ADDED so that replication can begin.
    In addition DNA synthesis occurs 5’—>3’ IN BOTH STRANDS.

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