Molecular Machines on the Move
Discoveries about the cell's machinery continue to mount. Here's a quick rundown of new findings from the scientific literature about molecular machines, with links for those who want the details.
- Librarians: Before the genetic code can be read, genes must be made accessible. Sometimes to get to a gene, the library needs to be remodeled. A paper in PNAS discusses "chromatin remodeling complexes, or remodelers, which are typically large, multisubunit complexes that use an ATPase subunit to translocate the DNA." (Emphasis added.)
- Electricians: Another paper in PNAS (open access) begins, "Voltage-gated ion channels support electrochemical activity in cells and are largely responsible for information flow throughout the nervous systems." The paper digs deeper into the voltage sensing of the channels.
- Men at work: In some species, males must deliver centrioles to the zygote. A paper in PNAS states, "Our data suggest that the same specialized meiotic mechanisms that function to prevent premature release of sister chromatid cohesion during meiosis I in C. elegans also function to inhibit centriole separation at meiosis II, thereby ensuring that the zygote inherits the appropriate complement of chromosomes and centrioles."
- Traffic cops: Dyneins, kinesins and myosins are among the "motor proteins" that act like molecular trucks for transporting cargo around the cell on highways of actin or microtubules. Like human truckers, they face obstacles. What controls the traffic flow at intersections? Another paper on PNAS looks into the rules of the road in cellular "cargo transport" and finds right-of-way rules, suggesting a "high degree of regulation of motor activity to maintain transport in a given direction."
- Electronic gatekeepers: The nuclear pore complex (and it is complex) is the gatekeeper to the nucleus. This paper in PNAS shows that electrostatic interactions help ferry the cargo through the gate: "The positive electrostatic potential facilitates the translocation of negatively charged particles."
- Locksmiths: "To ensure that the genetic material is equally and accurately distributed to the two daughter cells during cell division, the DNA fibers must have an ordered structure and be closely packed," Science Daily reports. The article is accompanied by an intriguing image of molecular padlocks that hold DNA strands together in a process that "ensures order in the DNA packaging process."
- Multitasking translator: "The ribosome has traditionally been viewed as the cell's molecular machine, automatically chugging along, synthesizing proteins the cell needs to carry out the functions of life," an article on PhysOrg says, preparing us for the surprise discovery that the ribosome is "More than a Machine." New research "reveals that the ribosome is not just an automatic molecular machine but instead also acts as a translational regulator."
- Watchmakers: Another article on PhysOrg describes "Watching the cogwheels of the biological clock" in living cells. "Our master circadian clock resides in a small group of about 10,000 neurons in the brain, called the suprachiasmatic nucleus," the article begins. "However, similar clocks are ticking in nearly all cells of the body." How appropriate this was discovered by Swiss researchers, who "devised an elegant method to watch directly under the microscope how the clock's molecular 'cogwheels' govern the activity rhythms" of an essential protein.
Speaking of biological clocks brings to mind to some philosophical discussions in past centuries about watches and watchmakers. What if William Paley had known that living cells really are in many ways built like finely crafted timepieces? Here are more papers on biological clocks for those wishing to look into the subject further.
- "The Circadian Clock Coordinates Ribosome Biogenesis" (PLoS Biology)
- "Rhythmic Changes in Gene Activation Power the Circadian Clock" (PLoS Biology)
- "Genome-Wide RNA Polymerase II Profiles and RNA Accumulation Reveal Kinetics of Transcription and Associated Epigenetic Changes During Diurnal Cycles" (PLoS Biology)
- "Rhythmic Ca2+ Signaling: Keeping Time with MicroRNAs" (Current Biology): "Pacemaker cells are specialized cell types that drive biological rhythms like the heartbeat and intestinal peristalsis. What determines whether a cell functions as a pacemaker? Studies in Caenorhabditis elegans suggest that pacemaking activity may be controlled in part by microRNAs."
- "Circadian Rhythms: An Electric Jolt to the Clock" (Current Biology): "The animal circadian pacemaker is composed of two transcriptional feedback loops, which regulate electrical activity in circadian neurons. Surprisingly, a new study reports that electrical activity can reprogram circadian transcription, and identifies CREB proteins as candidates for this reprograming."
Back in 1998, Bruce Alberts stated that the "biology of the future" was going to be the study of molecular machines (see here). He was correct; the journals can't get enough of the organic robots that carry on the functions of the cell. As scientists focus on the intricacies of molecular machines, they seem to find it less fruitful to talk about Darwin. With researchers thinking more and more in terms of engineering design, biology is moving along the right track.