3.6.3
Niacin (vitamin B3) Niacin, which comprises two compounds, nicotinic acid and nicotinamide, also occurs widely in food and is added to many breakfast cereals. It is easily absorbed into the blood from the digestive system and plays a vital role in energy production in cells. It appears to reduce the levels of low density lipoproteins or LDLs in the blood and increase high density lipoproteins or HDLs, perhaps by affecting the proteins that carry the fats. This is important because LDLs are a way of transporting
3.4 Vitamin E Vitamin E is not a single compound, but consists of a group of eight closely related chemicals, of which the most important, responsible for about 90% of its activity in the body is alpha-tocopherol. Since, like vitamins A and D, vitamin E is fat-soluble, it occurs in fat-rich foods. The main sources in the UK diet are from plant oils such as soya, corn and olive oil. Other good sources include nuts and seeds, and wheatgerm (the part of the wheat grain that will develop into the new plant) an
1.1 Introduction to vitamins and why we need them Before the 19th century, one of the hazards of long sea voyages was a condition called scurvy, whose symptoms were loss of hair and teeth, bleeding gums, very slow healing of wounds, and eventually death. Hundreds of sailors and explorers died from scurvy until a Scottish physician, James Lind, in the 1750s discovered that adding a daily portion of citrus fruit to the rations of those at sea could prevent the condition, whereas adding cider, vinegar or various other substances that he tested,
1.8 Enter aspirin! Aspirin is able to release part of its ester group (Figure 15) in a hydrolysis reaction. Look again at the structure of aspirin, 2.8, and identify this group on the molecule. It is known as an acetyl group and accounts for aspirin also being called acetylsalicylic acid. The acetyl group on aspirin is fairly easily removed and can be available for forming another ester with an —OH group on another molecule; in this case, part of the structure that makes up the inside of the cavi
1.2 How does it hurt? This is a useful question because once we know the mechanism of pain sensation we can do something about alleviating it. When tissue is injured there follows a rapid release of ‘messenger’ chemicals that stimulate the nerve endings. Electrical impulses are relayed through the nerves to the spinal column and to the brain, which registers the sensation of pain. It usually, but not always, also directs our attention to the site where the damaged tissue initiated the pain message.
Introduction In this unit you will find out that the sensation of pain is caused by the release of a chemical called prostaglandin that stimulates the nerve endings and sends an electrical message to the brain. Inhibiting the formation of prostaglandin reduces pain and we will see, by looking at the specific shape of the molecules involved, how aspirin can so inhibit the formation of prostaglandin. To make the most of the material of this unit you will need to use an organic molecular modelling kit such a
1.2.3 The transmission of genetic material The full complement of 46 chromosomes in the human genome, the diploid number, is restored at fertilization. As Figure 3.1 shows, all the somatic cells and cells in the testes and ovaries arise from the same fertilized egg by the process of mitosis; the cells all contain copies of the same genetic material (with some exceptions). 1.1.1 Inheritance of characters Imagine you have found some old family photograph albums which span many generations. What are the distinctive family features, or characters, that demonstrate the relatedness of individuals? In other words, what characters do they have in common? For example, they might have brown eyes, a white forelock in their hair, ears that are closely attached to the head, that is, without lobes. But you will also notice the striking differences between related individuals. For example, they may differ Learning outcomes After studying this unit you should understand: that genes are the units of inheritance for individual characteristics and also may contribute to susceptibility to certain diseases; the number of chromosomes that make up the human genome and where they are located within the cell; something of the immense scale of the human genome project; how gametes are produced by the process of meiosis and how the full complement of 46 chromosomes 2.3.1 Perfect diamagnetism Diamagnetism is due to currents induced in atomic orbitals by an applied magnetic field. The induced currents produce a magnetisation within the diamagnetic material that opposes the applied field, and the magnetisation disappears when the applied field is removed. However, this effect is very small: the magnetisation generally reduces the applied field by less than one part in 105 within the material. In diamagnetic material, B = μμ0H 3.6 End of seciton exercises After reading Section 3 you might conduct one of the following three exercises as part of your Portfolio evidence of achievement. You may like to discuss this activity with your supervisor.
Exercise 1
Demonstrate that you can communicate in an en 1.7.5 Theory Again, research is conducted in a context of existing ideas, evidence, and thinking. One key skill is the demonstration of cognisance of the theoretical context and of how it shapes your own research, including: understanding key theoretical strands and theoretical concepts in your discipline understanding how theory shapes your research question the ability to contribute something useful to the theoretical debate in 5.2 Neural ageing: article 1 Now read Neural Ageing Article 1: Concar, D. (2001) ‘Forever young’, New Scientist, 171, pp. 26–27. Click to view 'Concar article' Introduction The material presented in this unit is taken from SD805 ‘Issues in Brain and Behaviour’ – a 60-point postgraduate course within the Frontiers in Medical Science strand of The Open University's M.Sc in Science Programme. SD805 consists of two topics that are of immense worldwide social, economic, ethical, and political importance – ‘Addiction’ and ‘Author(s): 2.1.2 Diffraction and interference of light When light, or indeed any type of wave, passes through a narrow aperture, it will spread out on the other side. This is the phenomenon of diffraction. For example Figure 17 shows the diffraction of water waves in a device called a ripple tank. The extent to which waves are diffracted depends on the size of the aperture rel 1.7 Summary of Section 1 and questions Converging lenses or mirrors cause parallel beams of light to be brought to a focus at the focal point, situated at a distance of one focal length beyond the lens or one focal length in front of the mirror. Diverging lenses or mirrors cause parallel beams of light to diverge as if emanating from the focal point of the lens or mirror. Light paths are reversible, so a converging lens or mirror may also act as a collimator and 1.5.4 Image scale The nearest equivalent definition to angular magnification that is applicable to telescopes used for imaging onto a detector is the image scale (sometimes called the plate scale). Because of the importance of angular measures, the image scale quoted by astronomers indicates how a given angular measure on the sky corresponds to a given physical dimension in an image. The most common convention is to state how many arcseconds on the sky corresponds to 1 mm in the image. Fort 1.5.3 Angular magnification You may be familiar with the scales that appear on terrestrial maps or images obtained with microscopes, possibly stated as 1 : 100 000 or 1 mm corresponds to 1 μm. Scales such as these indicate how the size of the reproduction compares to the real thing. Image scales are no less important in astronomy, though they are usually stated in a different form, as we now explain. Imagine for a moment that you have the use of a telescope that allows you to observe Saturn and its ring system. It must 1.4.1 Deciduous trees During the winter months, a combination of factors, including lower temperatures, reduced light intensity and shorter days, means that plants can only photosynthesise at a slow rate and for restricted periods. As a result, photosynthesis cannot produce energy as fast as respiration expends it. In addition, water is often in short supply because of freezing, and so plants that do not have adaptations to conserve water, as conifers do, would lose water. Deciduous trees avoid these problems in w 1.2.1 The molecular level It is common knowledge that the freezing point of pure water is 0°C. Often, however, the temperature of water can fall below 0°C without it freezing, for two reasons: Any solvent containing a dissolved substance has a lower freezing point than when pure, which is why the sea freezes at a lower temperature than clean freshwater. The occurrence of supercooling, the phenomenon by which a fluid remains liquid at a temperature below
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Portfolio exercises
