Biology, 27.07.2019 15:00 alimfelipe

In which direction does the replication fork move as dna replication occurs?

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Answer from: nellys2096

DNA replication occurs in the 5 prime (5') to 3 prime (3') direction.
I'm sure you've heard this many times. I tutor in genetics, and all of my students can rattle that off. Less understand what it means.

First, understanding what 5' and 3' mean is important. DNA is composed of a ribose sugar, a phosphate group, and a base (A,T,G,C). The sugar has a phosphate group attached to its fifth carbon, and a hydroxyl group on its 3rd carbon. Nucleotides (separate components of DNA) are linked by the phosphate group and the hydroxyl group. So, every nucleotide is linked at the phosphate group and the hydroxyl group besides two - the two nucleotides at either end of the strand of DNA. The one that leaves a phosphate group exposed is called the 5' end of DNA, and the one that leaves a hydroxyl group exposed is called the 3' end of DNA.

A problem with many students just memorizing that replication occurs in the 5' to 3' direction is that there are two strands of DNA involved in replication. DNA polymerase (the major enzyme responsible for replication) reads the already existing strand of DNA in the 3' to 5' direction, and creates the new strand of DNA in the 5' to 3' direction (meaning that it adds nucleotides to the 3' end of the new strand).

Answer from: Quest

you are certainly talking about this picture:

a: is the label of the white square, it is showing the replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes the dna with the dna template and increases the processivity of the enzyme. ==> stops polymerase from falling off the template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built in the opposite sense of the helicase, so dna will be built in fragments ==> built fragments from 5' to 3 joins

and finally f: is the enzyme that builds the new dna strand (dna polymerase) ==> adds nucleotides to make a new dna helix.

credit: gradman555p98x9p

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