1865
Mendel’s Genetics • Clifford A. Pickover
Gregor Johann Mendel (1822–1884)
The Austrian priest Gregor Mendel studied the inheritance of easily identifiable traits in pea plants, such as color or wrinkling, and showed that the inheritance could be understood in terms of mathematical laws and ratios. Although his work was not recognized in his lifetime, the laws that he discovered formed the foundation of genetics—the science of heredity and variation in organisms.
In 1865, Mendel reported on his studies of more than 20,000 pea plants, conducted over six years, which led him to formulate his laws of genetics. He observed that organisms inherit traits via discrete units that we now refer to as genes. This finding was in contrast to other popular theories of his time, such as an individual inheriting a smooth blend of traits from the parents, or an individual inheriting “acquired characteristics” from their parents (such as a son having large muscles simply because his father lifted weights).
As an example, consider that in peas, each plant has two alleles (versions) of each gene, and that the offspring inherit one allele from each parent. It is a matter of chance which gene from each parent is received. If the offspring receives a gene for a yellow seed together with a gene for a green seed, the yellow gene may dominate in the offspring, but the gene for green is still present and is transmitted to the plant’s descendants in a consistent and predictable manner.
Today, medical geneticists aim to understand how genetic variations play a role in human health and disease. For example, the disease cystic fibrosis, which includes difficulty breathing among other symptoms, is caused by a mutation (change) in a single gene that affects membranes of cells. The ideas associated with Mendel’s genetics eventually led to a better understanding of genes and chromosomes (composed of a DNA molecule containing many genes), along with the potential to cure many diseases and shape the evolution of the human species. Human genes have even been placed into bacteria to create large quantities of insulin for diabetic individuals.
SEE ALSO Chromosomal Theory of Inheritance (1902), Epigenetics (1983), Human Genome Project (2003), Gene Therapy (2016).
Gregor Mendel studied the inheritance of easily identifiable traits in pea plants, such as color or wrinkling, and showed that inheritance could be understood in terms of simple mathematical ratios.
1869
Periodic Table • Derek B. Lowe
Lothar Meyer (1830–1895), Dmitri Ivanovich Mendeleev (1834–1907), John Alexander Reina Newlands (1837–1898), Antonius van den Broek (1870–1926), Henry Gwyn Jeffreys Moseley (1887–1915)
The periodic table is the undisputed centerpiece of chemistry. Built into its arrangement is a wealth of hard-earned knowledge about atomic structure, reactivity, bonding, and other crucial concepts. The building blocks of our world are all there, organized in a way that shows their deepest relations.
German chemist Lothar Meyer and English chemist John Alexander Reina Newlands were two of the first to realize (independently) that arranging the known elements by their atomic weights revealed underlying patterns. Elements with similar behavior tended to cluster together (such as sodium and potassium, both soft, highly reactive metals). In Russia, chemist Dmitri Ivanovich Mendeleev, unaware of the work of Meyer and Newlands, was thinking along the same lines, and in 1869 he presented his own arrangement based on atomic weights and the number of bonds the various elements tended to form. It not only had all the known elements, but it also boldly included gaps where new ones were predicted to exist. Their discovery (and the successful prediction of their properties) was powerful evidence that Mendeleev had it right.
Modern tables are ordered by increasing atomic number (the number of protons in the nucleus), as suggested by Dutch physicist Antonius van den Broek and by the work of English physicist Henry Gwyn Jeffreys Moseley. The columns (called groups) represent increasing numbers of electrons in each atom’s outermost “shell” (called an orbital), from just one electron on the far left column (reactive sodium and its alkali metal group members) over to the unreactive noble gases on the far right, with their perfectly filled orbitals. Then a new row (called a period) starts, with a heavier alkali metal on one end, going all the way over to a heavier noble gas. The heavier elements demonstrate the greater number of electrons that go into the outer orbitals, and the table spreads out accordingly.
It’s no exaggeration to say that many of the chemistry advances over thousands of years were leading up to this: Understanding how the elements differ and why has been one of the great works of the human race.
SEE ALSO Electron (1897), Atomic Nucleus (1911), Hydrogen Bonding (1920).
The current periodic table, where all of chemistry begins.
1874
Cantor’s Transfinite Numbers • Clifford A. Pickover
Georg Cantor (1845–1918)
German mathematician Georg Cantor founded modern set theory and introduced the mind-boggling concept of transfinite numbers that can be used to denote the relative “sizes” of an infinite collection of objects. The smallest transfinite number is called aleph-nought, written as ℵ0, which counts the number of integers. If the number of integers is infinite (with ℵ0 members), are there yet higher levels of infinity? It turns out that even though there are an infinite number of integers, rational numbers (numbers that can be expressed as fractions), and irrational numbers (like the square root of 2 that cannot be expressed as a fraction), the infinite number of irrationals is in some sense greater than the infinite number of rationals or integers. Similarly, there are more real numbers (which include rational and irrational numbers) than there are integers.
Cantor’s shocking concepts about infinity drew widespread criticism—which likely contributed to Cantor’s bouts of severe depression and multiple institutionalizations—before being accepted as a fundamental theory. Cantor also equated his concept of the Absolute Infinite, which transcended the transfinite numbers, with God. He wrote, “I entertain no doubts as to the truths of the transfinites, which I recognized with God’s help and which, in their diversity, I have studied for more than twenty years.” In 1884, Cantor wrote to Swedish mathematician Gösta Mittag-Leffler explaining that he was not the creator of his new work, but merely a reporter. God had provided the inspiration, leaving Cantor only responsible for the organization and style of his papers. Cantor said that he knew that transfinites were real because “God had told me so,” and it would have diminished God’s power had God only created finite numbers. Mathematician David Hilbert described Cantor’s work as “the finest product of mathematical genius and one of the supreme achievements of purely intellectual human activity.”
SEE ALSO Sieve of Eratosthenes (c. 240 BCE) Transcendental Numbers (1844), Gödel’s Theorem (1931).
Photo of Georg Cantor and his wife, taken around 1880. Cantor’s startling ideas about infinity initially drew widespread criticism, which may have exacerbated his severe and chronic battles with depression.
1875
Boltzmann’s Entropy Equation • Clifford A. Pickover
Ludwig Eduard Boltzmann (1844–1906)
“One drop of ink may make a million think,” says an old proverb. Austrian physicist Ludwig Boltzmann was fascinated by statistical thermodynamics, which focuses on the mathematical properties of large numbers of particles in a system, including ink molecules in water. In 1875, he formulated a mathematical relationship between entropy S (roughly, the disorder of a system) and the number of possible states of the system W in a compact expression: S = k∙log W. Here, k is Boltzmann’s constant.
Consider a drop of ink in water. According to Kinetic Theory, the molecules are in constant random motion and always rearranging themselves. We assume that all possible arrangements are equally probable. Because most of the arrangements of ink molecules do not correspond to a drop of clustered ink molecules, most of the time we will not observe a drop. Mixing occurs spontaneously simply because so many more arrangements exist that are
mixed than that are not. A spontaneous process occurs because it produces the most probable final state. Using the formula S = k∙log W, we can calculate the entropy and can understand why the more states that exist, the greater the entropy. A state with a high probability (e.g. a mixed ink state) has a large value for the entropy, and a spontaneous process produces the final state of greatest entropy, which is another way of stating the Second Law of Thermodynamics. Using the terminology of thermodynamics, we can say that there are a number of ways W (number of microstates) that exist to create a particular macrostate—in our case, a mixed state of ink in a glass of water.
Although Boltzmann’s idea of deriving thermodynamics by visualizing molecules in a system seems obvious to us today, many physicists of his time criticized the concept of atoms. Repeated clashes with other physicists, combined with an apparent lifelong struggle with bipolar disorder, may have contributed to the physicist’s suicide in 1906 while on vacation with his wife and daughter. His famous entropy equation is engraved on his tombstone in Vienna.
SEE ALSO Brownian Motion (1827), Second Law of Thermodynamics (1850), Kinetic Theory (1859).
LEFT: Ludwig Eduard Boltzmann. RIGHT: Imagine that all possible arrangements of ink and water molecules are equally probable. Because most of the arrangements do not correspond to a drop of clustered ink molecules, most of the time we will not observe a droplet once the ink drop is added.
1876
Gibbs Free Energy • Derek B. Lowe
Josiah Willard Gibbs (1839–1903)
If you want to look under the hood of chemistry and see what really makes things work, study thermodynamics. It measures changes in energy, the driving force for all chemical processes. Credit here goes to American scientist Josiah Willard Gibbs, whose theoretical insights and great mathematical ability turned thermodynamics into a precise scientific tool with applications in every possible area of chemistry, physics, and biology.
In 1876, he published his work on chemical systems and the “free energy” of reactions (now called Gibbs free energy, or G, in his honor). When a system changes from one state into another (chemically, as in a reaction, or physically, as in melting or boiling), the change in G (called ∆G or delta-G) is the work exchanged by the system with its surroundings (for example, the heat that is given off). Chemical reactions that can spontaneously give off energy show a negative ∆G. A fire is a perfect example. Reactions that have even larger negative ∆G values (such as the thermite reaction or the decomposition of nitroglycerine) can be dangerously energetic. In contrast, reactions with a positive ∆G—photosynthesis in plants, for example—require the addition of external energy, such as sunlight.
The other key thing to know about ∆G is that it’s made up of two parts: enthalpy and entropy. Enthalpy (designated by the letter H) can be thought of as a pure measure of heat and energy, while entropy (S) is related to disorder and the reactants’ “degrees of freedom” (i.e., how many different ways that they can move and vibrate). Chemists think in these terms constantly, gaining great insight into reactions by keeping all these factors in mind.
Some chemical reactions are spontaneous even though they actually get cold and soak up heat from their surroundings, like an instant “cold pack.” This can happen because the entropy of the final state is so much higher (∆S) than that of the starting materials, canceling out an unfavorable enthalpy change (∆H), and giving an overall favorable ∆G. If both ∆H and ∆S are large and negative, though, you have an explosion in the making!
SEE ALSO Conservation of Energy (1843), Second Law of Thermodynamics (1850), Boltzmann’s Entropy Equation (1875).
LEFT: Josiah Willard Gibbs, 1903. RIGHT: This explosive thermite reaction has a large negative ∆G value.
1876
Telephone • Marshall Brain
Alexander Graham Bell (1847–1922)
Imagine that the year is 1850 and you want to talk to someone. You have exactly one option: You can travel and meet with that person face-to-face, which could take days or weeks, depending on distance. Your alternative: a handwritten letter. Or, by 1850, the telegraph system has started to expand. But the simple act of talking to someone still requires a face-to-face meeting.
Enter the telephone. The patent for Alexander Graham Bell’s telephone was issued in 1876. The device itself was incredibly simple—a microphone made of carbon granules and a speaker. To connect two telephones together, all you needed was copper wire and a small source of electric current, like a battery—with this innovation, two people talked to each other at a distance for the first time.
How did engineers scale this up? The first innovation was the central office. In a town, copper wires ran from each home or business to the central office. An operator could connect any line to any other line in town. Wires are added to connect the town to the next town over. At that point, anyone in the two towns could communicate. As additional towns connected, this led to the creation of regional central offices. Eventually trunk lines spanned the country, then the world, and now everyone could connect to everyone else.
Engineers developed mechanical switches to replace the human operators. The telephone dial told the switches what to do. As a result, the cost of calling fell. Engineers created much smaller computers to replace the mechanical switches, and touch-tone dialing became possible. The cost of calling fell again. Engineers turned voice signals into digital bits and sent the bits through fiber optic cables, drastically reducing costs and increasing capacity. Then engineers created voice over IP (VoIP) so calls were routed through the Internet. Internet telephony was born and calling became free on many VoIP networks. The success story for engineering: taking something that used to be impossible and eventually making it free!
SEE ALSO Telegraph System (1837), Fiber Optics (1841), Radio Station (1920), ARPANET (1969).
Bell Telephone Company, America. Engraving from Scientific American, 1884.
1878
Enzymes • Michael C. Gerald with Gloria E. Gerald
Wilhelm Kühne (1837–1900), Eduard Buchner (1860–1917), James B. Summer (1887–1955)
Life cannot exist without enzymes. Thousands of chemical reactions occur in living cells: old cells are being replaced by new ones; simple molecules link to form complex ones; food is digested and converted to energy; waste materials are disposed of; and cells reproduce. These reactions, involving buildup and breakdown, are collectively referred to as metabolism. For each of these reactions to occur, a certain degree of energy is required (activation energy) and in the absence of such energy, these reactions would not occur spontaneously. The presence of these enzymes—which are usually proteins or RNA enzymes—reduces the amount of activation energy required for these reactions to occur and increases the rate of these reactions by millions. In the process, enzymes are neither consumed nor chemically changed.
Each of the chemical reactions in the body is a component of a pathway or cycle, and most enzymes are highly specific and act on only a single substrate (reactant) in the pathway to produce a product in the metabolic sequence. Most of the more than 4,000 enzymes in living cells are proteins, with a unique three-dimensional configuration, the shape of which accounts for their specificity. An enzyme is commonly named by adding the suffix ase to the root name of the substrate on which it acts, although more specific (and descriptive) names are used in chemically oriented literature.
It was known in the late seventeenth and early eighteenth centuries that meat was digested by secretions in the stomach and starch could be broken down to simple sugars by saliva and plant extracts. Wilhelm Kühne, a German physiologist, was the first to coin the name enzyme in 1878 to refer to trypsin, a protein-digesting enzyme he had discovered, and, in 1897, Eduard Buchner at the University of Berlin first demonstrated that enzymes could function outside living cells. In 1926, working with the jack bean, James Summer at Cornell University isolated and crystallized the first enzyme, urease, and provided conclusive proof that it was a protein. Summer was the co-
recipient of the 1946 Nobel Prize in Chemistry.
SEE ALSO Cellular Respiration (1937), Ribosomes (1955), Polymerase Chain Reaction (1983).
Certain anticancer and immunosuppressive drugs target purine nucleoside phosphorylase (PNP), an enzyme that carries out housekeeping functions by clearing away certain waste molecules that are formed when DNA is broken down. The image depicts a computer-generated model of PNP.
1878
Incandescent Light Bulb • Clifford A. Pickover
Joseph Wilson Swan (1828–1914), Thomas Alva Edison (1847–1931)
The American inventor Thomas Edison, best known for his development of the light bulb, once wrote, “To invent you need a good imagination and a pile of junk.” Edison was not the only person to have invented a version of the incandescent light bulb—that is, a light source that makes use of heat-driven light emissions. Other equally notable inventors include Joseph Swan of England. However Edison is best remembered because of the combination of factors he helped to promote—a long-lasting filament, the use of a higher vacuum within the bulb than others were able to produce, and a power distribution system that would make the light bulb of practical value in buildings, streets, and communities.
In an incandescent light bulb, an electric current passes through the filament, heating it to produce light. A glass enclosure prevents oxygen in the air from oxidizing and destroying the hot filament. One of the greatest challenges was to find the most effective material for the filament. Edison’s carbonized filament of bamboo could emit light for more than 1,200 hours. Today, a filament made of tungsten wire is often used, and the bulb is filled with an inert gas such as argon to reduce evaporation of material from the filament. Coiled wires increase the efficiency, and the filament within a typical 60-watt, 120-volt bulb is actually 22.8 inches (580 millimeters) in length.
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