A- DNA replication

DNA replication is a biological process by which a molecule of DNA is copied. This process starts at the origin of replication where the double helix of the parental DNA is being unwound by the helicase in two separated strands. Then, single-strand biding proteins bind on the unpaired strands keeping them from repairing. The topoisomerase helps relieve the strain by breaking and swiveling the DNA strands ahead of the replication fork. The primase synthesize a short stretch of RNA called primer, which is the initial nucleotide chain synthesize during DNA replication. DNA-polymerase catalyzes the synthesis of new DNA by adding nucleotide to the preexisting chain of RNA. The double strands of the DNA is originated in opposite direction this why they form an antiparallel structure. The strand formed in same direction as the replication fork progress is called the leading strand and the one formed is the opposition direction of the fork is called the lagging strand. We have to notice that the lagging strand is synthesized discontinuously as a series of segment called Okazaki fragments. These fragments are joined together by the DNA ligase to form a continuous DNA strand.

B- RNA transcription

Transcription is the synthesis of RNA using the information in the DNA. The stretch of DNA that is transcribed into an RNA molecule is called the transcription unit. The transcription is divided into three stages:
1. Initiation, during this stage, RNA polymerase binds to the promoter located on DNA strands. In eukaryote, some proteins called transcription factors bind to the promoter and mediate the binding of RNA polymerase what forms the transcription initiation complex, which mark the beginning of