DNA replication: The "speed" of DNA polymerase

During DNA replication, DNA polymerase adds bases that pair to the bases already present in the template DNA strand. The average distance between consecutive base pairs in a DNA strand is 3.4 Angstroms (1 Angstrom = 10${}^{-10}$‍ m). DNA polymerase can replicate a DNA strand even as it follows the twists and bends of the DNA strand.

Figure 1 DNA polymerase replicating template strand

The DNA polymerase molecule can form new base pairs quickly. However, quantifying its maximum replication rate is difficult, because individual polymerase molecules can accelerate, decelerate, pause, or fall off the template strand. Polymerase replication rates are often reported in base pairs per second (bp/s).

Researchers determined the maximum replication rate of individual DNA polymerase molecules by measuring the elasticity of single strands of DNA as they were being replicated. The total number of bases in the DNA molecule, N(total), was known. The elasticity of the molecule at each point in time was compared with the known elasticities of single-stranded and double-stranded DNA of length N(total), in order to infer the percentage of the DNA molecule that had been replicated, p(t). Researchers used p(t) to determine the number of base pairs replicated at any given time, as shown in Equation 1.

Equation 1 N(t) = p(t) x N(total)

Results of this analysis are shown below.

Figure 2 Activity of a single DNA polymerase molecule