4.1 The varied structures of RNA RNA is a versatile cellular molecule with the ability to adopt a number of complex structural conformations. Although RNA is often thought of as a single-stranded molecule it is actually highly structured. 2.4 Analysis of nucleic acids by electrophoresis and hybridisation Nucleic acids can be separated according to size by gel electrophoresis, most commonly performed using a horizontal gel (Figure 7a). This is in contrast to the vertical gel electrophoresis set-up, which is generally used for analysis of proteins. The size of DNA molecules is usually expressed in terms of the number of 1.2 Nucleic acids: genetic, functional and structural roles in the cell The first role that one immediately thinks about for nucleic acids is that of an inherited genetic material, principally in the form of DNA. In some cases, the inherited genetic material is RNA instead of DNA. For example, almost 60% of all characterised viruses have RNA genomes and these are more common in plant viruses than in animal viruses. There is considerable variation in the amount of genetic material present within organisms (Author(s): Learning outcomes After studying this unit you should be able to: define and use each of the terms printed in bold in the text; understand the properties of nucleotides, how they contribute to secondary and tertiary structures of nucleic acids at the molecular level, and how torsional states are maintained in cellular DNA; understand the different composition and roles of nucleic acids in the cell and their interactions with each other and with agents that cau 4.5 Generating carbon — the legacy of volcanoes What is the origin of the carbon within the carbon cycle? Figure 1.9 showed that the greatest proportion of the global carbon store is locked into car 4.1.1 Identifying the pregnacy Our description of the developing embryo has, so to speak, detached it from its mother. But we should remember that on the other end of the placenta is a woman whose reaction to her pregnancy may lie almost anywhere in the scale of human emotion, and whose behaviour during her pregnancy will have an enormous effect on its outcome. This section attempts to look at the pregnancy from the mother's point of view. Of course, it cannot possibly be applicable to all women in all pregna 1.2.1 Decoupling sex and reproduction Humans have separated sex and reproduction: unlike other species, we can enjoy sexual intercourse even (or especially) at times when fertilization is not possible. Many sexual encounters are casual, and in these cases it is often very important to avoid pregnancy. Even during long-term relationships, many couples choose to avoid having children. Thus for many people contraceptive measures are an essential part of their lives. This is not a modern phenomenon: as you will see, birth control has Conclusion The rate at which water infiltrates into the ground depends on the permeability of the rocks and the state of the ground surface. Below the ground surface there is an unsaturated zone which has air in the pore spaces, and a saturated zone which has all the pores filled with water. The water table is the boundary between the unsaturated zone and the saturated zone, and is the level at which water stands in wells. Water below the water table is called groundwa Learning outcomes After studying this course, you should be able to: use information from wells, the topography of the ground and a water table contour map, to carry out the following: interpret cross-sections, calculate the thickness of the unsaturated zone, and the rate of groundwater flow; deduce the direction in which groundwater is flowing; and estimate the depth to the saline interface in a coastal area from the height of the water table list the types of rock that usually ma 5 Biomass conversion of solar energy Photosynthesis in the geological past was responsible for all fossil fuel reserves, but its products are buried about 2000 times more slowly than we use them at present. The total carbon content of all biomass growing on land is estimated to be 5.6 × 1014 kg and, as Figure 10 shows, about one-fifth of this mass is renewed each year. Figure 6 shows how modern plant biomass is distributed across the continents. Clearly, biological conversion of solar energy to a chemical form in com Learning outcomes After studying this course, you should be able to: explain the principles that underlie the ability of various natural phenomena to deliver solar energy outline the technologies that are used to harness the power of solar energy discuss the positive and negative aspects of solar energy in relation to natural and human aspects of the environment. 6 Direct heating using geothermal energy In the same way that waste heat from conventional power stations can be used for direct heating of buildings, and in industrial production and horticulture, low-grade geothermal energy has considerable potential. Many existing developments, such as those in Iceland, use spent fluids from geothermal electricity generation. Areas of natural hot springs are an obvious target, but it is also relatively simple to exploit normal heat flow using either natural groundwater or a variety of heat-exchan 4.3 The UK's coal reserves Production of large quantities of coal in the UK during the 19th and 20th centuries led to the progressive depletion of reserves. In 2005 underground mining was limited to the Carboniferous coalfields of Yorkshire and the East Midlands, with only one underground mine operating in South Wales. However, surface mining sites still work coal in most of the coalfields (Author(s): 4.1 Global coal reserves Having looked in detail at how coal is mined, this section focuses on those areas of the world that produce it. It begins by looking at how and why reserves of coal are distributed throughout the UK and Europe, before reviewing the current global reserves of coal. 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 rootlets are p Conclusion This free course provided an introduction to studying the arts and humanities. It took you through a series of exercises designed to develop your approach to study and learning at a distance and helped to improve your confidence as an independent learner. 7.4 Proteomics Traditionally, the study of the biochemistry or structure of a protein necessitated its purification to a high degree. The development of protocols for cloning, manipulation and expression of genes greatly facilitated this kind of study, as will be clear to you from the previous section. In recent years, a number of high-throughput techniques have, to an extent, obviated traditional approaches and permit simultaneous analysis of all the expressed proteins in a cell or organism, known as the < 7.3.1 Physical methods for demonstrating an interaction between proteins To identify those unknown proteins in a complex mixture that interact with a particular protein of interest, protein affinity chromatography can be used (Figure 49a). This approach uses a ‘bait’ protein attached to a matrix. When this baited matrix material is then exposed to a mixture of proteins, only proteins that interact with th 2.4 The covalent modification of proteins Many proteins are modified by the covalent linking of groups that can affect their function and/or localisation in the cell. Such covalent modifications occur after synthesis and folding of the polypeptide component. The main types of covalent modification and their functions are listed below. Methylation/acetylation of amino acids at the N-terminal tails of histone proteins in eukaryotes can affect the structure of chromatin and ultimately gene 1.3.1 Helices A variety of helical structures can be identified in proteins using X-ray diffraction. A helix can be described by the number of units (amino acid residues) per turn (n) and by its pitch (p), which is the distance that the helix rises along its axis per turn. These parameters are indicated in Figure 8 for a number of helice
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