Chapter 12, Problem 16A

Summary Introduction

To determine:

The correct statement about the elongation of lagging strand.

Introduction:

DNA replication a process by which DNA makes copies of itself and this requires lots of enzymes to complete the process. DNA replication occurs in three stages namely, Initiation, Elongation, and Termination.

Explanation of Solution

Initiation: During initiation, a short piece of RNA known as RNA primer, bind to one of the strands of DNA called leading strand, and this acts as starting point for DNA synthesis.

Elongation: During the elongation process, DNA polymerase binds to the leading strand of DNA and synthesizes the new DNA by pairing bases of template strands to their complementary bases.

One of the template strands of DNA is read in a 3’ to 5’ direction, which means that the new strand will be formed in a 5’ to 3’ direction. This newly formed strand is referred to as the Leading Strand. Only oneRNA primer is required to initiate DNA polymerase, during synthesis of leading strand as the process is occurring in a continuous manner. This is because DNA polymerase is able to extend the new DNA strand by reading the template 3' to 5', synthesizing in a 5' to 3' direction.

The other template strand or lagging strand is antiparallel, and is read in a 5’ to 3’ direction. As the helix unwinds, new RNA primers are added to the newly exposed bases on the lagging strand and DNA synthesis occurs in fragments,known as Okazaki fragments. The DNA synthesis of this strand also occurs in the 5' to 3' direction but many RNA primers are required during the synthesis of lagging strand.

The DNA synthesis of this strand also occurs in the 5' to 3' direction but many RNA primers are required during the synthesis of lagging strand.

Termination: The process of expanding the new DNA strands continues until there is either no more DNA template left to replicate.The okazaki fragments are then joined by the enzyme DNA ligase.