3.3 Uranium production and economics Table 3 lists the major uranium-producing countries. Currently, Canada (with 29% of global supply in 2003) is the world's largest producer of uranium, followed by Australia (21%), both having increased production since about 1980, whereas production from the USA, France, and South Africa has declined (
1.6 Impurities in coal Coal rank reflects the maturity of a coal, but another variable is the ratio of combustible organic matter to inorganic impurities found within the coal. As discussed earlier, impurities result mainly from clay minerals washed into the mire prior to its eventual burial. In addition, some impurities are formed from the plant material itself during coalification. These inorganic impurities are non-combustible and therefore leave an inert residue or ash after coal combustion. High-a
1.4 Coal-forming environments in the geological record Figure 5 simplifies a typical vertical succession of sedimentary rocks found in many coalfields. The sequence from the base of the section upwards reveals the following: When a mire starts to form, the first plants take root in underlying clays or sands that form the soil. Their r
4.2 Summary Glycogen metabolism is controlled by two enzymes, glycogen synthase (mediating glycogen synthesis) and phosphorylase (mediating glycogen breakdown). Three pathways converge in the regulation of glycogen synthase: cAMP/PKA and GSK-3β are negative regulators, whereas ISPK/PP1G positively regulate the activity of glycogen synthase. Insulin and adrenalin have opposite effects on glycogen synthesis: insulin promotes glycogen synthes
3.6 Protein kinases Protein kinases phosphorylate proteins either at tyrosine residues (tyrosine kinases), or at serine and threonine residues (serine–threonine kinases), or on any of these three amino acids (dual-specificity kinases). All these activities are employed in signal transduction pathways (histidine kinases also operate in certain plant and bacterial pathways, but not in animals). You should now be familiar with receptor tyrosine kinases, and have seen in some detail how phosph
Learning outcomes By the end of this unit you should be able to: define and use each of the terms printed in bold in the text. understand the basic principles of signal transduction mechanisms, in particular the concepts of response specificity, signal amplitude and duration, signal integration and intracellular location; give examples of different types of extracellular signals and receptors, and explain their functional significance; describe
7.2 Site-directed mutagenesis The application of site-directed mutagenesis (SDM) to the study of protein function has been illustrated with the enzyme lysozyme, as described previously. SDM is a very powerful technique in the study of protein function, allowing the experimenter to assess the importance of particular amino acid side-chains in a protein. It is most commonly used in the study of enzymes; however, it is also very useful in identifying key residues in protein–protein interactions. In this section, we will co
5.3.1 Allosteric regulation In many proteins, the binding of a particular ligand at one site affects the conformation of a second remote binding site for another ligand on the same protein. This effect is called allosteric regulation and it is an important mechanism by which a protein's binding capacity and/or its activity are regulated. Thus the switch between two different protein conformations can be controlled by binding of a regulatory ligand. 1.4.3 Protein domains An important concept in protein structure is that of the protein domain. In many cases, a single polypeptide can be seen to contain two or more physically distinct substructures, known as domains. Often linked by a flexible hinge region, these domains are compact and stable, with a hydrophobic core. Domains fold independently of the rest of the polypeptide, satisfying most of their residue–residue contacts internally. Typically, two or more layers of secondary structural elements eff 9 Summary Active galactic nuclei (AGN) are powered by accretion onto supermassive black holes. The masses of these central engines of AGN can be estimated by means of the virial theorem, using the size of the nucleus of the galaxy and the velocity dispersion of the material in the vicinity of the nucleus. Estimates of the masses are around 109±1 M 7.4 Faraday depolarization Radiation of wavelength λ which starts off linearly polarized in a particular direction and travels through a plasma has its direction of polarization rotated by an angle where ne is the electron density, B| | is the component of the m 1.3.4 Predicting the outcome of crosses By knowing the pattern of inheritance of genes as described above, it is possible to make some predictions about the phenotypes and genotypes of each generation in breeding experiments. This section considers some examples of such predictions. First consider whether it is possible to determine the genotype for certain characters, such as grain colour, from observing an organism's phenotype. 4 How to diagnose diabetes Diabetes is a condition that results in an increased concentration of blood glucose and for diagnosis, accurate measurements of blood glucose levels are required. Blood glucose levels can be measured on different samples of blood. Sometimes the whole of the blood sample is used. This occurs when finger prick samples are measured on small personal meters. For more accurate measurements, the sample of blood is taken to a laboratory and the blood cells are removed. Measurements are then made on 9 Managing the BSE/vCJD episode from May 1990 to March 1996 The discovery of FSE in the domestic cat and TSEs in antelopes of five different species (Section 4) – plus laboratory transmission of BSE to a pig – confirmed the transferability of BSE between species. The ban on SBO was therefore extended from September 1990 to cover all animal feed (including pet food). At 5.4 Coping with heat Not only are there the mechanisms to generate extra heat, but there are cooling mechanisms too, of which sweating is just one example. Watch ‘A Winning Design’ on the DVD from 30.50–34.12 and write down the behavi Learning outcomes By the end of this unit you should be able to: explain the distinctive biological features of monotremes; distinguish contrasting modes of reproduction in monotremes, marsupials and placental mammals; describe the cellular basis of lactation and explain the benefits of an early diet of milk; explain the significance of mammalian metabolic rate; explain how and why the thermogenic response differs amongst species; 1.6.3 The acceleration due to gravity In the absence of air resistance, an object falling freely under the influence of the Earth's gravity, close to the surface of the Earth, experiences an acceleration of about 9.81 m s−2 in the downward direction. The precise value of the magnitude is indicated by the symbol g and varies slightly from place to place due to variations in surface altitude, the effect of the Earth's rotation and variations in the internal composition of the Earth. Some typical values f 1.4.7 A note on straight-line graphs and their gradients We end this section by reviewing some of the important features of straight-line graphs, though we do so in terms of two general variables z and y, rather than x and t, in order to emphasise their generality. If the graph of z against y is a straight line of the kind shown in Figure 22, then z and y are related by an equation of the form Introduction Motion is vital to life, and to science. In many ways it was the investigation of motion, initiated by Galileo Galilei in the late sixteenth century, and brought to a head by Isaac Newton in the seventeenth, that inaugurated the modern era of physics. Progress since that time has been so great that describing motion is now regarded as a fundamental part of science rather than one of its frontiers. Nonetheless, the description of motion played a central role in Einstein's formulation of the sp 6.3.2 Crystal Almost all modern gamma cameras use (thallium-doped) sodium iodide (NaI) as the scintillation crystal. A gamma photon interacts with the crystal to produce many photons of visible light. Sodium iodide is hygroscopic so cannot be left exposed to the air. The front surface is coated with a low atomic number metal that allows the gamma photons to pass through. The rear surface is covered with a transparent coating so that the visible photons can pass through to the photomultiplier tubes.
Author(s):
Activity 4
