Topoisomerase Breaks The DNA Binding Site Helicase

For growth and development, every cell requires its full fledging machinery to duplicate, so for DNA as well. For initiation of replication requires energy and enzymes. DNA is double stranded helix which requires linear conformation for replication. So to help it out special enzymes and proteins bind to it. Topoisomerase cuts the DNA strand and made path for helicase to bind to DNA strand. Helicase plays part in unwinding of DNA helix so that to facilitate other replicative machinery to bind to DNA(Pope et al., 2001). The two strands of DNA are unzipped by this motor protein. It mostly performs its activity by converting chemical energy to mechanical energy. Helicase is hexameric molecule with different nucleotide binding sites with different affinities for NTPs. The two binding

It releases the energy dissipation. How helicase actually works is still unknown but there are recently three proposed models which include Plough-share model, rotary pump model and steric exclusion model(Ding and Liu, 2015). Once DNA strand unwound the RNA primase form primer to 3’end of new strand so that DNA polymerase easily held to the strand and add nucleotides to the strand which are already freely available in nucleus. The energy provided to DNA polymerase comes from breakage of bonding by helicase and also by nucleotides(Edwards et al., 2015). The hydrogen bond between GC is stronger as compared to AT, so energy dissipation also depends on the quantity of presence of GC content. The ORC complex that binds to DNA strand also have ATP binding site “special sequence” to which ATP molecule bind. Mutation in sequence led the inhibition of ATP to bind. DNA polymerase uses energy from NTPs that are freely present in nucleus. NTPs by hydrolysis with help of RNA polymerase form primer on which DNA pol adds nucleotides. DNA ligase by using NAD+ into NMN+ +AMP or ATP into PPi and AMP ligate the