Tuesday, September 03, 2013

Practical science

On Sunday Sept 1, I gave a lecture at AACI Netanya in their "Coffee and..." series on the subject of "Practical Science", based on several blogs I had written in the past.

Many people think of science as a remote and difficult subject. But, actually science is all around us and is part of our lives all the time. Here are some examples that might intrigue you.

· How does a towel work? Water has an intrinsic surface tension that results in capillary action, namely water rises in a capillary, the narrower the diameter the higher the rise. This is because the forces that hold the water molecules tegether are unequal at the surface. This effect is used for example when a drop of blood is collected into a capillary. In a towel, capillary action causes the water to cling to the narrow spaces within the weave of the towel and results in a drying effect

· Why is hair curly or frizzy when dry and lank when wet? Water causes a change in the structure of the protein called keratin that makes up hair; the dry form is a bent or helical structure (frizzy or curled hair) and the wet form is an extended one. This was discovered by William Astbury in 1936 when he did X-ray diffraction patterns of wool kertatin in dry and wet conditions in Leeds and observed two different patterns. These were called the a and b-forms, the former shortened into a helix and the latter elongated. The same experiment was done with DNA fibers by Rosalind Franklin in 1952 showing that there are two forms of DNA, the A and B-forms. It was the latter form at high humidity that gave a relatively simple X-pattern in the x-ray diffraction photo that allowed Francis Crick to determine that the structure was a helix, and that led to the formulation of the Watson-Crick double helical model for DNA.

· How does a detergent work? The detergent has a combination of water-soluble and oil-soluble parts joined together chemically, so it is capable of causing oil and water to mix, in effect to dissolve in each other. The ionic part of the molecule is termed hydrophilic (loves water) and the tail portion is hydrophobic (hates water, i.e. is fat soluble) and so the bifunctional detergent molecule allows the solubilizatrion of fat into water.

· Why does transparent egg white form a solid white substance when heated? This is due to the denaturation of the lysozyme protein that makes up the egg white and once this change happens it is irreversible. Proteins are made up of strings of amino acids linked together like beads on a necklace. But, it is the folded structure or conformation that gives the proteins their native structure and function, for example the enzymes of the gut that degrade food. When proteins are heated above a certain tempertature they denature or unfold and become random structures that have no activity and intertwine around each other forming a white opaque solid. This is what happens when we boil an egg. This is the basis of sterilization, by heating things in boiling water, this denatures the proteins of any microorganisms that are present and in effect kills them.

· How does electromagnetism work? Electricity and magnetism are intimately connected and an electrical generator works on the same principle as an electromagnet. If you run an electic current through a wire this produces a magnetic field, for example if you wind a wire solenoid around a piece of iron, you can induce it to be magnetized and to pick up paper clips or other metal objects. Equally, if you pass a wire through a magnetic field you produce a current in the wire. This is how electricity is produced, except that many thousands or millions of wires are turned rapidly thru magnetic fields in huge generators turned by steam and this produces electricity, that is then distributed throughout towns and cities.

· How can water be turned into blood or wine? With the appropriate chemical it can appear to happen. For example a few crystals of the substance potassium permanganate can turn a large volume of water a deep red color. This might explain how people supposedly turned water into wine or blood.

· How can chemical substances in a complex mixture be separated? Applying a complex mixture of substances, such as green chlorophyll extracted from plants, onto filter paper then allowing a solvent (such as alcohol) to spread them out, the components can be seen as colored bands. Thus, it was found that there are 8 different chemical components in chlorophyll. This simple process is called chromatography, or the study of colors, but actually it involves the separation of chemical substances that don't have to be colored but can be detected by other means, such as UV light. When this method of chromatography is applied on a large scale, pure components can be isolated and their chemical structures determined.

· How can diamonds and graphite be the same substance? Diamonds and graphite are both forms of carbon, yet they have entirely different properties that are dependent on their totally different chemical structures. In diamonds the carbon atoms are joined together in the form of many tetrahedra, that give the structure a very hard and crystalline form, but in graphite the carbon atoms are joined together in separate planes, that can slide over each other and makes the whole structure soft and so it is used in pencils.

· How do drugs work? Someone once asked me how do drugs know where to go in the body? Of course, they don't, this is teleological, drugs don't know anything. Drugs work at the molecular level by binding to specific binding sites of proteins into which they fit, something like a baseball fitting into a glove. Usually this causes a molecular change in the protein, called a conformational change that triggers biochemical and physiological responses. Often drugs enter cells by transiting their cell wall or membrane. But, often there is a transmembrane receptor protein, that spans the cell wall, many of which have 7 transmembrane elements. When the drug moleclue binds to an outside receptor element, it causes a change in the macromolecular structure, which in turn triggers an intracellular biochemical event. So drug action can be very complex.

Science is the nearest thing we have to magic. In fact a lot of what was considered magic in the distant past can be explained by subsequent scientific knowledge. The explanations given here should enhance understanding of the world around us.


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