Protein-Tracking Microscope
According to the original article, the first ever high-powered compound binocular microscope that is so sensitive as to track the real-time motion of a single protein to the level of its individual atoms has been designed by Stanford University. It allowed researchers to settle debates about the way the genes are copied from DNA – a biochemical process that is essential to life.
This type of high-powered compound binocular microscope has infrared light to trap and control the forces on a functional protein, and allows the monitoring of molecules. The measurements were accurate to 1 anaptrom, or, one-tenth of a anometer which is 10 times finer than any precious measurements.
In their study, published in Native, Block and his colleagues, dealt on the biological dogma that in living organisms, genetic information flows from DNA to RNA to proteins. The DNA is similar to a twisted ladder, in that it has two strands connected by molecular rungs called bases, identifiable by abbreviations as A.T. G and C. This ladder contains genes that encode thousands of proteins which keep the organism alive. Misplacement or substitution of letters in its sequence in the DNA can produce a defective protein and may cause a serious disease.
One crucial step in this dogma is the transcription where each gene is copied from DNA onto RNA beginning with an enzyme called RNA polymerose (RNAP) which latches onto the DNA ladder, pull a small section apart, then builds a new complimentary strand of RNA that copies each base to an exposed strand and finally moves down the strand until the gene is fully copied.
Transcription process at molecular level is still being debated by scientists as to the question of whether the RNAP enzyme actually climbs up the ladder one at a time or moves instead in chunks, called discontinuous elongation.
According to the article, two basic hypotheses were proposed:
1. RNAP moves along DNA inchworm-like, frontally;
2. RNAP pulls in (“scrunches”) a loop in DNA, copies each base grabs another loop farther up the ladder.
Whichever is the correct one has not been settled because no
conventional device, even a compound binocular microscope or other high-powered microscopes, can measure anything smaller than 10 anaptroms. However, since DNA lader bases are only about 3.4 anaptroms apart, scientific hard work is seen to be the answer to break this barrier.
To attain that goal, the block group had to overcome the two problems with conventional force clamps which are the fluctuating signals, and the bending of light waves.
Laser beams that shines through the air wiggle just as stars twinkle so that taking measurement of the position of anything that moves at even 1 angtrom is not possible. By sealing optics external to the microscope in a box the air which was replaced with helium, the researchers came-up with something that has 10 times less twinkling and with much more light stability.
Aside from light stabilization, the group have yet to improved on the method for detecting force and displacement.
Conventional force clamps use microscopic beads attached near the opposite ends of a long DNA molecule, resembling that of a dumbbell. One RNAP enzyme attaches to a bead, churns out a complimentary strand of RNA as it moves along with the two beads drawing close together, and usually held near the center of two separate optical traps. In the original article, a graduate student discovered that if one or two beads was placed near the outer edge of the trap, the force would remain constant allowing armostrong-level measurements to be made quickly and efficiently.
With these experiments, it appears that the two hypotheses of the discontinous elongation are inconsistent with the new data. The long-held idea that RNAP climbs the DNA ladder one base at a time is right after all.
Just what makes this molecular motors drive was presented in two models, the power stroke models and the Brownian (or thermal) model but Block and his colleagues favored the latter model without reaching out other power stroke models or absolutely acceptance of the thermal model.
With the years of careful instrument development through the sponsorship of Stanford University and many agencies, as well as dedication of graduate students, Dr. Block is simply proud of these outstanding outcome.
