DNA Replication Visible for the First Time

Microscopic image of DNA strands replicatingLike all living things on earth, your physical characteristics are determined by proteins – and the information for making those proteins is encoded in your DNA.

Life originated on earth about four billion years ago, possibly as soon as 500 million years after the planet’s formation. This suggests the inception of life may not be a massively unlikely occurrence, though it’s too early to know. The first planets around other stars were only detected in 1992, and though the NASA Exoplanet Archive lists 3,496 confirmed planets in 582 multi-planet systems, none has yet been shown to harbor any form of life.

To gain a deeper understanding of how life reproduces, we need to accurately model at an atomic level what happens as a DNA molecule replicates itself. The biologists building those models got a real boost this week when a team at the University of California (Davis) released of an 11-second movie that shows a single DNA molecule (from e. coli bacteria) unwinding and rewinding as its genetic information is copied.

The video is part of their report in the journal Cell (Independent and Stochastic Action of DNA Polymerases in the Replisome), and was created with fluorescent dyes and very high-speed imaging tools. The unprecedented view enabled researchers to watch molecular interactions unfolding in real time, and processes that were thought to move at a fixed speed were in fact seen to be speeding up and slowing down erratically.

(DNA replication starts when an enzyme called helicase unzips the famous double-helix staircase into two separate strands. Each DNA strand is made of four bases — A, T, C, and G — that connect in specific pairs to form rungs along the strands. A second primer enzyme attaches to each strand, then a third enzyme called polymeraseattaches to the primer, moving along with the strand and expanding as it adds more and more letters to form another double helix.)

The video shows individual glowing strands of DNA as they move from left to right while replicating, with the leading strand forging ahead, adding bases as it goes, while the lagging strand follows behind, reconnecting the double helix. Very cool.