How does replication of long DNA molecules occur? Explain the process.
(i) In long DNA molecules the two stands cannot be separated in its entire
length as a large amount of energy is required for this process.
(ii) This replication occurs within a small opening of DNA helix known as
(iii) DNA dependent DNA polymerase catalyses polymerisation of
nucleotides only in one direction, i.e., 5' -> 3'.
(iv) One on stand with polarity 3' -> 5' the replication is continuous and on
other with polarity 5' -> 3' it is discontinuous.
(v) The discontinuously synthesized fragments are later joined by the
enzyme DNA ligase.
(vi) The replication does not initiate randomly at any point in DNA. There
is a definite region in E.coli DNA where the replication originates . Such
regions are termed as origin of replication.
(vii) Replication is a very expensive process. Deoxyribonucleoside
triphosphate are used instead of nucleotides as they serve dual
purposes. That is -
* They act as substrate;
* They provide energy for polymerisation reaction (The two terminal
phosphates in a deoxyribonucleoside triphosphate are high energy
phosphates as in the case of ATP).