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The lagging strand must be synthesized in fragments, known as Okazaki fragments, because DNA is antiparallel and DNA polymerase can only synthesize new DNA in the 5' to 3' direction. As the replication fork opens, the lagging strand runs in the opposite direction, necessitating the formation of short segments that are later joined together. This allows for the continuous unwinding of the DNA helix while efficiently synthesizing the lagging strand.
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What is the definition of a lagging strand?
A lagging strand is one of two strands of DNA found at the replication fork, or junction, in the double helix; the other strand is called the leading strand. A lagging strand requires a slight delay before undergoing replication, and it must undergo replication discontinuously in small fragments.
What fragments of DNA produced from the lagging strand that must be joined called?
The fragments of DNA produced from the lagging strand that must be joined are called Okazaki fragments. These fragments are short sections of DNA that are synthesized in the 5' to 3' direction away from the replication fork during DNA replication. They are later sealed together by DNA ligase to form a continuous DNA strand.
Why are leading and lagging strand primers removed instead of being joined with Okazaki fragments during DNA replication?
Leading and lagging strand primers are removed during DNA replication because they are only needed temporarily to initiate the synthesis of new DNA strands. Once the Okazaki fragments are synthesized, the primers are no longer necessary and must be removed to allow for the joining of the fragments into a continuous DNA strand.
Why two strands of the helix have to be elongated by two slightly different mechanisms?
The two strands of the DNA helix are elongated by slightly different mechanisms due to the antiparallel orientation of the strands. DNA polymerase synthesizes the leading strand continuously in the 5’ to 3’ direction, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments. This difference arises because the lagging strand must be synthesized in the opposite direction to the unwinding of the helix, necessitating a different approach to elongation. Thus, the distinct mechanisms ensure efficient replication of both strands.
What are 4 events that must occur in the lagging strand?
In the lagging strand during DNA replication, four key events must occur: First, RNA primers are synthesized by primase to provide a starting point for DNA synthesis. Second, DNA polymerase adds nucleotides in short segments called Okazaki fragments, working away from the replication fork. Third, these fragments are later joined together by DNA ligase to create a continuous strand. Finally, the RNA primers are removed, and the gaps are filled in with DNA nucleotides.
Why is replication on one strand of DNA continuous while on the other strand the replication must be discontinuous?
DNA replication proceeds in opposite directions on the two strands of DNA due to their antiparallel structure. The leading strand is synthesized continuously towards the replication fork, while the lagging strand is synthesized discontinuously in segments called Okazaki fragments away from the replication fork. This difference is due to the need for primers to start each new DNA fragment on the lagging strand.
Describe the significance of Okazaki fragments?
Okazaki fragments are created during DNA replication because DNA Polymerase can only add nucleotides in a 5' to 3' direction. This means that one strand (the leading strand) can be continuously created, but the other strand (the lagging strand) runs in the opposite direction. This means that loops must be created and shorter parts of DNA replicated one at a time. This creates fragments on the lagging strand. The RNA primers on this strand are later replaced with DNA by DNA Polymerase I, and joined together with DNA ligase.
Why is the leading strand considered continuous?
The leading strand is the correct orientation, so it can be replicated continuosly - meaning the DNA Polymerase can continue to add new nucleotides without stopping. New DNA strands can only be created in a 5' to 3' direction. This is different to the lagging strand - which must be looped and copied in small, non-continuos segments. These segments are known as Okazaki fragments.
Why lagging strand is fragmented?
Think of DNA as a zipper. The left one labelled 5' on the top and 3' on the bottom. The right one labelled 3' on the top and 5' on the bottom. ex. left 5'-------------------------3' right 3'-------------------------5' As you 'unzip' (with helicase), the teeth of the zipper are exposed. The copying mechanism moves along the original strand in a 5' to 3' direction ex left 5'------ .....................\ .......................--------------------3' .......................--------------------5' ....................../ right 3'------ (periods are merely space holders ignore them) On the 'left' strand, the DNA Polymerase attaches to the free 5' end and moves toward the helicase On the 'right' strand, the DNA Polymerase must attach near the helicase (zipper-handle) and move towards the top. It must start several times therefore lagging strands are fragmented.
What enzymes must be present for DNA replication to proceed normally?
For DNA replication to proceed normally, several key enzymes are required, including DNA helicase, which unwinds the double-stranded DNA, and DNA polymerase, which synthesizes new DNA strands by adding nucleotides complementary to the template strand. Additionally, primase is necessary to synthesize RNA primers, providing a starting point for DNA polymerase. Finally, DNA ligase is essential for joining Okazaki fragments on the lagging strand, ensuring the newly synthesized DNA is continuous.
What are leading strands?
the two strand are antiparallel and the new strand must be formed on the old(parent) strand in opposite directions one of the new strand is formed as a continuous occur in long chain in the 5'_3' directions on 3'_5' strand of dna this is called the leading strand..
Why are there many replication forks?
A replication fork is the mechanism by which a strand of DNA is synthesized. If you can imagine a strand of DNA unwound, then it would resemble a ladder. Unzip the DNA and it now looks like a fork, ie fork in road, not eating fork. There is a Leading strand, which is synthesised easily. USing DNA polymerase which 'reads' along the strand in the 3' to 5' direction on the strand, producing a replication strand in the 5' to 3' direction. The opposite strand is called the lagging strand, and this is slightly more complicated. DNA polymerase cannot read in the 5' to 3' direction on the template strand. Thus DNA primase is used to read the strand and replicate small RNA segments, called Okazaki fragments. The lagging strand has no been copied into many small strands of RNA, or Okazaki fragments. Next DNA polymerase comes along and replaces all the RNA nucleotides with DNA nucleotides. ANd finally DNA ligase 'stitches' all the small fragments into one long strand.
