In: Biology
1) Explain three main steps in the process of DNA replication. Name the enzyme that goes with each step.
2) In which direction are new nucleotides added during replication?
3) What is the difference between leading and lagging strand?
4) Which enzyme is responsible for "unzipping" the DNA double helix?
1.Three main steps in the process of DNA replication along with the enzyme that goes with each step are as follows:-
a. Initiation-- Enzyme- MCM HELICASE that unwinds the DNA double strand, TOPOISOMERASE reduces the supercoiling strain caused due to unwinding of the helics. RNA PRIMASE adds the short strand of RNA primer for the elongation of DNA.
b. ELONGATION--- DNA POLYMERASE l removes the RNA primer by the 5'-3' exonuclease activity. DNA POLYMERASE III adds the nucleotide and leads to the elongation of the DNA strand.
c.Termination---- Enzyme- NUCLEASES proof reads the newly synthesized strand and removes the mismatch pair bases. DNA POLYMERASE II fills the gap created due to excision of bases. finally, the DNA is joined by the LIGASE and process is completed.
2. New nucleotides are added in 5'--3' direction during replication.
3. Leading strand is the strand of DNA which is synthesized in the direction same as the replication fork. The nascent DNA synthesis is continuous .
whereas lagging strand is the strand of DNA whose direction of synthesis is opposite of the direction of the replication fork. The lagging strand is synthesized in short, separated segments called as okazaki fragments, which are later on joined by the ligase after the excison of RNA primer.
4. DNA HELICASE is responsible for "unzipping" the DNA double helixs by breaking the hydrogen bonds between nitrogenous bases.