User:Betaclamp/Sandbox/Semi-discontinuous replication

Semidiscontinuous replication is a term that describes a particular type of double-strand (ds) DNA replication.

Replication is the copying of DNA. Semidiscontinuous describes the process by which the situation, namely that DNA may be copied in only one direction yet the native conformation of two strands of DNA together has them linked in opposite directions, is dealt with. Its necessity is due to the following two intricately linked reasons.

First, a single strand of DNA has a directionality: call the 5' (five-prime) end the top and the 3' (three-prime) end the bottom. The holoenzyme that copies DNA may do so only in one direction, from 5' to 3'.

Second, when two single DNA strands (molecules) combine to form a DNA double helix, they lie opposite each other: see antiparallel/Biochemistry; also see complementary.

The semi in semidiscontinuous refers to the fact that the actions of mechanism are different for each strand. The 5' - 3' strand, that a polymerase can copy nicely in that direction, is replicated continuously; while the 3' - 5' strand must be copied in segments discontinuously, in a "backward" fashion.

The continuous copying occurs on the "leading" strand, the other is called the "lagging" strand. The segments of DNA that are synthesized individually and then ligated together to form an intact copy of the lagging strand are called Okazaki fragments.

Semiconservative replication
A related concept is "semiconservative replication." Semiconservative relates simply to the facts that when the two strands of Dna in a parental duplex molecule are separated for copying, the structure of each is unchanged (conserved) but they do not recombine. Each daughter duplex winds up with half original and half (semi) newly synthesized material.

Minor Compendium of internal links :

1) Good, in place :  Complementary Dna - nice, expansive, actually a separate topic.

Complementary - needs ranking -

2) Good, need reassignment : have 2 in the wings to relocate -

3) Iffy and Bad :  Complementation (genetics)  -  dislocate -

4) Others : Complementarity (molecular biology)  -  v short, no refs, 2005 attempt to merge with  complementary.                     Complementation  redirects to  Complement  -  which is ultra-general.