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Terence Allen
More books by Terence Allen…
“Long before the idea of scanning specimens with a small spot of light produced confocal light microscopy, the idea of using a small spot of electrons to scan surfaces had been around for as long as electron microscopy itself. A surface demarcates the boundary of a solid, and is the site of interaction with the surrounding environment, from a ball bearing to a living cell. In the mechanical world, adhesion, friction, wear, and corrosion are all dependent upon surface properties. The smooth surface of a ball bearing is crucial in the reduction of friction, but its efficiency may well be compromised by wear or corrosion.”
― Microscopy: A Very Short Introduction
― Microscopy: A Very Short Introduction
“In our own bodies, only the liver is capable of limited regeneration, but chop a limb off a starfish or a salamander, and it will grow a new one. We are starting to understand the molecular signals that are used by these species to regenerate limbs in adult life. Mammals seem to only use this signalling pathway during the growth of the early embryo but it is a pathway that may well have the potential to be reactivated. Following surgical removal, the wings can grow back in embryonic chickens when the production of a protein called wnt is switched on. Frog limb regeneration can also take place later in the life cycle when wnt protein is expressed. Tadpoles have this ability but it is normally lost when they metamorphose into frogs. The expression of wnt signalling protein around an injury is thought to cause a reprogramming or transdifferentiation of mature cells into stem cells capable of producing the cell types needed for the limb. Very young children have been known to re-grow severed fingertips, and so there are intriguing possibilities for human tissue regeneration.”
― The Cell: A Very Short Introduction
― The Cell: A Very Short Introduction
“The actual mechanics of cell division, according to Dick McIntosh at the University of Denver, require significantly more instructions than it takes to build a moon rocket or supercomputer. First of all, the cell needs to duplicate all of its molecules, that is DNA, RNA, proteins, lipids, etc. At the organelle level, several hundred mitochondria, large areas of ER, new Golgi bodies, cytoskeletal structures, and ribosomes by the million all need to be duplicated so that the daughter cells have enough resources to grow and, in turn, divide themselves. All these processes make up the ‘cell cycle’. Some cells will divide on a daily basis, others live for decades without dividing. The cell cycle is divided into phases, starting with interphase, the period between cell divisions (about 23 hours), and mitosis (M phase), the actual process of separating the original into two daughter cells (about 1 hour). Interphase is further split into three distinct periods: gap 1 (G1, 4–6 hours), a synthesis phase (S, 12 hours), and gap 2 (G2, 4–6 hours). Generally, cells continue to grow throughout interphase, but DNA replication is restricted to the S phase. At the end of G1 there is a checkpoint. If nutrient and energy levels are insufficient for DNA synthesis, the cell is diverted into a phase called G0. In 2001 Tim Hunt, Paul Nurse, and Leeland Hartwell received the Nobel Prize for their work in discovering how the cell cycle is controlled. Tim Hunt found a set of proteins called cyclins, which accumulate during specific stages of the cell cycle. Once the right level is reached, the cell is ‘allowed’ to progress to the next stage and the cyclins are destroyed. Cyclins then start to build up again, keeping a score of the progress at each point of the cycle, and only allowing progression to the next stage if the correct cyclin level has been reached.”
― The Cell: A Very Short Introduction
― The Cell: A Very Short Introduction
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