During DNA replication in E. coli, the synthesis of each nascent strand occurs i

Question

During DNA replication in E. coli, the synthesis of each nascent strand occurs in a different way. Leading strand synthesis occurs continuously in the 5' to 3' direction. Lagging strand synthesis occurs discontinuously, seemingly in the 3' to 5' direction. In order to regulate the synthesis of both strands, some enzymes and molecules are specific to leading or lagging strand synthesis, whereas others are involved in both processes. Categorize each of the following enzymes or molecules based on whether it is required for leading strand synthesis, lagging strand synthesis, or both types of synthesis. Leading strand synthesisagging strand synthesisBoth types of synthesis DNA gyrase DNA polymerase IlI DNA polymerase l p multiple RNA primers a single RNA primer rimase

Explanation / Answer

Ans. I. Leading strand synthesis: A single RNA primer,

II. Lagging strand synthesis: Multiple RNA primers

III. Both types of synthesis: Primase, DNA polymerase III, DNA pol I, DNA gyrase

# DNA polymerase I removes the RNA primer from both the leading and lagging strands with its 5’3’ exonuclease activity. DNA pol I also simultaneously replaces the RNA nucleotides with complementary dNTPs during removal of the primer.

# DNA pol III binds to both the leading and lagging template DNA strands and synthesizes complementary strands.

# Primase synthesizes RNA onto both the leading and lagging template DNA strands

# Leading strand synthesis requires relatively very few number of RNA primers compared to that of lagging strand. So, on a relative strand, there is 1 RNA primer on the leading strand whereas there are multiple RNA primers on lagging strand.

# DNA gyrase (topoisomerase II) binds to the lagging strand and relieves supercoiling strains by inducing stranded cuts on BOTH the strand and subsequent sealing.

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