When does DNA synthesis occur?
What is meant by leading and lagging strands?
Since this is not my area of expertise, I searched Google under the key words "DNA synthesis" to get these possible sources:
http://images.google.com/images?q=DNA+synthesis&hl=en&client=safari&rls=en&um=1&ie=UTF-8&sa=X&oi=images&ct=title
http://en.wikipedia.org/wiki/DNA_replication
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html
http://web.indstate.edu/thcme/mwking/dna.html
http://www.johnkyrk.com/DNAreplication.html
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. You can also search under "DNA leading lagging."
I hope this helps. Thanks for asking.
DNA synthesis, also known as DNA replication, occurs during the S phase of the cell cycle. This process takes place before cell division to ensure that each daughter cell receives an identical copy of the genetic material.
To understand the concept of leading and lagging strands in DNA replication, we need to look at the structure of DNA and how it is replicated.
DNA is made up of two complementary strands that are antiparallel to each other. One strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction.
During DNA replication, the double-stranded DNA unwinds and separates into two single strands. These strands serve as templates for the synthesis of new DNA strands.
The leading strand is the strand that is synthesized continuously in the 5' to 3' direction. Since DNA polymerase can only add nucleotides to the 3' end of a growing DNA strand, it can easily add nucleotides continuously to the leading strand in the same direction as the replication fork.
On the other hand, the lagging strand is synthesized discontinuously in the opposite or 3' to 5' direction. This occurs because the DNA polymerase can only add nucleotides to the 3' end, but the DNA strand is being unwound in the 5' to 3' direction. Therefore, the replication of the lagging strand occurs in short fragments called Okazaki fragments.
To synthesize the lagging strand, RNA primers are first synthesized by an enzyme called primase. DNA polymerase can then add nucleotides to the RNA primers, creating short fragments of DNA. These fragments are subsequently stitched together by another enzyme called DNA ligase to form a continuous strand.
In summary, leading and lagging strands refer to the two strands of DNA that are synthesized during DNA replication. The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments in the opposite or 3' to 5' direction.