Mere Biochemistry: Cell Division Involves Thousands of Complex, Interacting Parts

first_imgIn biochemistry, the stem -mere means “part” (as in centromere, telomere) and -some means “body” (as in chromosome, ribosome).  Biochemists are learning that these cell organelles are not -mere bit parts, but -some fit bodies.Telomeres and chromosomes:  PhysOrg reported that the chemical “caps” on the end of chromosomes, called telomeres, have a special code to keep them intact.  Scientists from Portugal and U of Indiana found that a histone tag near the telomeres keeps the DNA Damage team from tying separate chromosomes together – a response that would spell death for the cell.  “It’s amazing,” a Portuguese scientist remarked, “but it appears to be this single change that underlies the cell’s ability to distinguish the end of the chromosome (i.e. a telomere) from a break in the middle.”  Described as “like the plastic caps on shoelaces,” telomeres not only keep chromosomes intact, but are also implicated in the aging process as they wear off, or in cancer when they go awry.Ribosome quality control:  Cells need to search and destroy nascent proteins that fail to have a “stop code” when being translated in the ribosome.  PhysOrg reported that a quality control mechanism in bacteria that corrects or deletes failed polypeptides in the ribosomes operates similarly, but is unrelated to, the system in eukaryotes.  Scientists at the Scripps Research Institute used a “homology approach” to identify a protein in yeast that performs the same inspection role on nascent proteins that a different protein plays in bacteria.  “The [bacterial and eukaryotic] mechanisms are very different, but the concepts are remarkably similar,” one researcher said.  “—that’s the beauty of it.”  We know all about that.  Search engines are a concept, but the manifestations (Google, Bing) can be very different.Centromere code:  It goes without saying that heredity depends on accurate copying of DNA at each cell division.  PhysOrg reported on a finding at Pennsylvania School of Medicine that showed how the “histone code” epigenetically (i.e., apart from DNA inheritance) identifies the center of each chromosome – the centromere – so that the spindle apparatus accurately connects to it during cell division (see also 05/06/2010 and 12/17/2007).  Science Daily described how a “centromere identifier attracts other proteins, and in cell division builds a massive structure, the kinetochore, for pulling the duplicated chromosomes apart during cell division.”  The article quoted a researcher happily saying, “Our work gives us the first high-resolution view of the molecules that control genetic inheritance at cell division.  This is a big step forward in a puzzle that biologists have been chipping away at for over 150 years.”Telomere linemen:  Researchers at the Wistar Institute identified another key player in the cell’s task of keeping its chromosome ends (telomeres) intact.  A two-part protein named Cdc13, which has a “crucial support role in maintaining and lengthening telomeres,” is able to simultaneously grip the tail end of the telomere while recruiting the telomerase enzyme to add more cap units.  Emmanuel Skordalakes of Wistar had an interesting analogy to describe the action: “You can think of Cdc13 as if it were you hanging on to the edge of a cliff, with one grip stronger than the other,” he said.  “You’re going to keep that strong hand on the cliff’s edge while your weaker hand reaches into your pocket for your phone.”Centrosomes untangled:  Centromeres, centrosomes; what’s the difference?  Centromeres are the center parts of chromosomes where attachments are made to pull paired chromosomes apart during cell division.  The centrosome is also involved in cell division, but it is a “complex made up of several hundred different proteins,” reported Science Daily, that includes the centrioles and the spindle apparatus that winches the paired chromosomes apart.  In attempting to dissect differences between normal divisions and faulty ones, German biochemists investigating centrosomes in fruit flies “identified more than 250 different proteins making up this complex…. They found a whole series of proteins responsible for the separation of chromosomes, number of centrosomes and their structure.”  They hope their detective work will “unravel regulatory networks in the future, which will help to target and interfere with the division of cancer cells.”Switched-on mitosis:  A casual look at cells in identical circumstances seems to show them dividing at random.  Some scientists have preferred to think there is something inherent in a cell that tells it when to divide.  There is: a toggle switch.  Scientists at Duke University found a switch in the cell that determines which cells will divide, and which ones won’t.  PhysOrg said this “gene circuit” acts like a “bistable switch.”  The article explained, “The gene circuit is in all cells and can tell identical cells to live in two states simultaneously, either on or off.”  When the signal to divide comes, some respond, and some don’t.  This helps reconcile competing hypotheses about how cells know when it’s time to divide.  “Bistability is not unique to biology,” the article said.  In electrical engineering, for example, bistability describes the functioning of a toggle switch, a hinged switch that can assume either one of two positions – on or off.”  The bistable switch in the cell determines which cells will be the dividers and which will not.  “Genetic switch underlies noisy cell division” was PhysOrg’s headline.Coded chromosomes:  Cell division is like a symphony, reported Science Daily, describing what researchers at Rockefeller University have found.  They found hard evidence for the “histone code hypothesis,” the idea that tags on the histone proteins on which DNA is wound provide an independent epigenetic code, distinct from the DNA code, that affects heredity (for historical background, see 11/04/2002, 02/16/2004 and 07/26/2006).   “The orchestration of the exact timing and localization of the vast array of molecules and processes involved in reproducing the chromosomes is one of the basic wonders of biology and is at the core of both healthy living and diseases such as cancer, that arise when the process goes awry,” the article said.  “We cracked one code,” Hironori Funabiki, head of the Laboratory of Chromosome and Cell Biology at Rockefeller, said, “but there are yet many to be decoded to understand how chromosomes orchestrate mitosis.”PhysOrg reported that scientists at the University of Edinburgh “were able to define some 4,000 proteins involved in the division of cells.”  These proteins “protect the fragile genetic material and help it fold into the correct shape before it splits into two new cells.”  They were astonished at “the intricacies of this process” but had nothing to say about evolution.This is some of the de facto intelligent design research taking place around the world.  Keep pouring on the evidence: nothing in biology makes sense in the darkness of evolution; nothing in biology makes sense except in the light of intelligent design.(Visited 49 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img