1) Body cells connect to collagen by a special protein, named fibronectin, which at one end has binding sites for a special family of membrane proteins, called integrins. Along the length of fibronectin, there are a series of selective binding sites for collagen, fibrin (=blood clots) and several other extracellular structural proteins., blood clots. Fibronectin also sticks non-specifically to glass and plastic. Fibronectin was independently discovered and purified by four different researchers, each using a different criterion. One of these co-discoveries resulted from 2-dimensional chromatography & electrophoresis of all the proteins found in cancerous cells, as compared with the most closely related non-cancerous cells. There was one spot that was dramatically reduced in amount in the cancerous cells. One of the other independent studies was a comparison of commercially-bought batches of calf serum. Tissue culture media traditionally contains 10% calf serum; and you buy this serum from meat packing companies, sometimes indirectly. Some batches produce much more cell locomotion ("spreading", "growth") than others. A post-doc was assigned to find out what was missing in the bad batches, present in the good batches, and could by itself produce much better cell spreading. Until then, the dominant opinion was that plasma membranes themselves adhered to external materials by forming "calcium bridges". That was because if you reduce the concentration of calcium and magnesium ions, cells will detach from glass, plastic and each other. This effect is mostly because the cell cortex becomes much more flexible when Ca and Mg are reduced, and gets pulled out in strands. 2) Genes are made of DNA. This was discovered using transfer of genes between pneumonia-causing bacteria. Some members of a certain species were fatal (to mice and humans), and had "smooth" patterns of growth in culture, with both these properties resulting from sugar polymers on their outer surfaces. Mutant forms of the same species formed "rough" colonies, had different surface sugars, and were much less lethal. Griffith had discovered in the 1920s that if you injected mice with some of the rough bacteria, plus molecules from killed bacteria of the harmful smooth strain, then not only would the mice die, but you could culture smooth bacteria from them. Oswald Avery & 2 co-workers, in the late 1940s, tested which kinds of molecules from the "rough" bacteria had the power to transfer this genetic property. They expected it would either be a protein, or possibly it would be those sugar polymers that give colonies of bacteria that smooth outline. They bravely grew the killing bacteria in 20 and 50 gallon glass carboys, killed them, and separated proteins, RNA, DNA and other components from each other, and tested which purified substance could convert rough bacteria to smooth (killing) bacteria. To their surprise, "the transforming factor" was DNA. Many or most scientists refused to believe them, much less to believe that the genetic material for all genes in all life forms is DNA. People said it is impossible to encode that much information in just four alternatives. They wrote that using 26 letters of the alphabet. Avery and his collaborators did not win the Nobel Prize. Alfred Hershey and Martha Chase used bacteriophages labeled with radioactive sulfur and radioactive phosphorous. They infected large numbers of bacteria with these viruses, and then quickly put them in a Waring blender, to knock off all the viruses, and centrifuged the bacteria separate from the viruses. Proteins contain sulfur and DNA contains phosphorous. Only the radioactive phosphate entered the bacteria. Hershey received the Nobel Prize, but Chase didnŐt. 3) The mutations produced by a certain chemical dye (acridine orange) have the strange property that triple mutants are often normal. Organisms with just one or two of these point mutations had very abnormal properties, but some with 3 mutations behaved almost normal. These are "frame shift mutations". 1=bad, 1+1=bad, 1+1+1=OK. These fell into two categories. Some had lost individual base pairs; others had gained base pairs. An organism with one mutation from each category would be normal. 1-1=OK. Ask yourself if you would have been able to figure out the meaning of these results. 4) From what did mitochondria and chloroplasts evolve? They evolved from commensal bacteria and blue-green algae (Procaryotic algae). They reproduce by splitting in two; if entirely lost, cells cannot make more. Many organisms have commensal algae and some have commensal bacteria, that can live separately. Mitochondria and chloroplasts have DNA; chloroplasts have about as much per chloroplast as regular bacteria have per cell! This DNA codes for proteins that are found in mitochondria or chloroplasts. Recombination was used to make genetic maps of their genes. Mitochondria and chloroplasts are damaged by streptomycin-type antibiotics, that specifically damage the prokaryote type of ribosomes, and donŐt hurt eucaryote ribosomes. When ribosomes were purified from chloroplasts and mitochondria, they had the size of prokaryotic ribosomes. 5) Energy from oxidation reactions is used to pump hydrogen ions (which it is a mistake to call "protons", because they are really H3O1 +, and often H11O5 +) through the inner membrane of mitochondria and the innermost membrane of chloroplasts. These hydrogen ions then leak back past special rotating enzymes (called ATP synthase) that transfer the energy to the formation of ATP from ADP. Incidentally, the chemical bonds formed are not "high energy". The ATP phosphate bonds are extremely low energy bonds. The inventor of the idea of "chemiosmosis" won the Nobel Prize for it. It was published in 1961. The acidity around isolated mitochondria, and inside them, changes as they make ATP from ADP, and their ATP-making ability can be changed by adjusting the acidity of the fluid around them. 6) When skeletal muscles contract, myosin molecular slide actively past fibers made of actin. Myosin is an ATPase. Transmission electron microscope pictures eventually could see both the thin (actin) fibers and the thick (myosin) fibers; what clinched it were comparisons of EMs of muscles fixed when relaxed, as compared with muscles fixed when contracted. You can see neither thick or thin fibers get shorter, but the amount of overlap between them increases by exactly the same proportion as the muscle had contracted. 7) What causes the active bending of cilia and flagella of animals and plants. For a while, the microtubules were assumed to contract. But Peter Satir at Einstein Med School made electron microscope sections through cilia that had been fixed (locked in position by chemical cross-linking) when bent the maximum amount in one direction, and other cilia that had been fixed when maxiimally bent in the opposite direction. He discovered (proved) that the outermost ends of the outer nine doublet microtubules extend further on the side of the cilia toward which it is bending. This proved that the microtubules arenŐt getting shorter, which they should have done if they were contracting. Another researcher isolated flagella, removed the membranes, and partially digested the proteins that hold the microtubules in place: then these flagella were exposed to ATP, the outer 9 microtubules sheared past each other like sections of an extendable ladder. Dynein was then discovered to be the ATPase that pulls one microtubule along another, but it was a surprise when this was also found in the cytoplasm, being used to transport vesicles along microtubules, originally in nerve axon cytoplasm. 8) What bacterial flagella do that is different than animal cell flagella. They are stiff helices, like bed springs, that are rotated by a motor protein at their base. The first clue was that particles stuck to individual bacteria often spin round and round, especially if they are stuck by antibodies against the protein that the flagella are made out of. Similarly, bacteria that get stuck to slides by their flagella will spin rapidly (the whole bacterial cell spins, because a flagellum is stuck down). 9) A particular communicable virus of chickens was discovered to produce sarcoma cancers in them. This was in 1911, and was not believed by most cancer researchers, although a Nobel Prize was given in the 1920s to a person who (mistakenly) claimed to have discovered a bacterium that causes cancer! Rous, the discoverer of the Sarcoma Virus got a Nobel Prize when he was about 80 years old, because it took that long for the main-stream to be convinced that he had been correct. Other cancer-causing viruses were found, and by their use it became possible to "do genetics" on whichever of their genes were the ones that converted cells to cancerous behavior. In most cases, and especially in RNA retroviruses, it turned out that just one of the genes in each of these viruses had the cancer-producing effect. Then came an even bigger surprise, which was that these cancer causing genes were mutant forms of genes normally found in the host species of animals. These "oncogenes" had accidentally been picked up by the viruses in some past infection. A big surprise for everyone. Most human cancers are caused by somatic mutations. 10) Ray Rappaport pushed a tiny glass bead down on the top of a sand dollar egg cell, so that the cell became shaped like a dough-nut. At the time of the second mitosis, three cleavage furrows formed. Two of these were not surprising, because they lined up with the equators of the two mitotic spindles. The third cleavage furrow was half-way between the poles of two different mitotic spindles! This third spindle it taken as proof that even when a normal cleavage furrow forms around the equator of a mitotic spindle, where the chromosomes collect in telophase, the signals that stimulate formation of the contractile ring come from the poles of the spindle, even though these are the parts of the spindle that is farthest from the cleavage furrow. It is still debated whether these signals strengthen cortical contraction, or weaken it.

 

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