3.5 A new life There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’, i.e. when a woman could feel her fetus moving inside her. However, both these opinions suffer from an underlying falsehood: that life ‘begins’ at all. Life is a continuum; gametes are produced by living parents, and fuse to produce new living individuals, but unfused gametes are n
4.3 Gamete production in men A sexually mature man is producing sperm all the time at a rate of around 300–600 per gram of testis per second. This provides the 500 million or so which are released at each ejaculation. But the formation of an individual sperm takes about nine weeks (64 days). Sperm are produced in the testes, and production is most efficient at a temperature several degrees lower than the normal body temperature of 371°C. For this reason the testes (plural of testis) are suspended outside the body cavi
8 Summary 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
6 Permeability It is important to distinguish clearly between porosity and permeability. Porosity is a measure of how much water can be stored in a rock, whereas permeability is a measure of the properties of a rock which determine how easily water and other fluids can flow through it (see Section 4). Permeability depends on the exte
1 Water underground Many people have the impression that underground water occupies vast caverns, such as those in the Derbyshire Peak District, flowing from one cavern to another along underground rivers. This is a common misconception: underground caverns are fairly rare, but huge quantities of water exist underground, within rocks. This is because many rocks contain pores, spaces that come in all shapes and sizes. In sediments, and consequently sedimentary rocks, there are often pores between gr
1 Wave energy The energy carried by ocean waves derives from a proportion of the wind energy transferred to the ocean surface by frictional drag. So, ultimately it stems from the proportion of incoming solar energy that drives air movement. Just how much energy is carried by a single wave depends on the wind speed and the area of ocean surface that it crosses; wave height, wavelength, and therefore wave energy, are functions of the distance or fetch over which the wind blows. Not surprisingly the ma
6 Summary Waterlogged organic matter accumulates in deltaic, coastal barrier or raised mires to form peat. Coal forms by the compaction and decomposition of peat. Chemical changes imposed by increasing temperature and pressure over time determine the coal rank. Coalfields can be classified as either exposed or concealed, depending on whether or not the coal-bearing rocks are hidden by younger strata. In most coalfields, mining commenced in the shallower
2.7 Summary Eukaryotic cells contain numerous distinct types of membrane-bound compartment. Transport vesicles move proteins and other molecules between the compartments. Proteins contain signalling sequences or patches that specify their destination compartment. Proteins destined for lysosomes, secretion or the plasma membrane are synthesised in the ER, transported to the cis Golgi, modified in the Golgi apparatus, and sorted and pa
1.7 Localization of signalling proteins Since signalling proteins cannot diffuse as rapidly as small second messengers, they need be close to their downstream target in order to be able to function. Where they are located with respect to both their subcellular position and their immediate neighbours is therefore vitally important. The plasma membrane is usually the initial location, and proteins can be attached to the plasma membrane in various ways (Author(s):
Acknowledgements Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged below is Proprietary and used under licence (not subject to Creative Commons licence). See Terms and Conditions. Figures 3, 5–7, 40, 41 Voet, D. and Voet, J. G. (1995) Biochemistry, 2nd edn, copyright © 1995 John Wiley & Sons Inc Figures 4, 8, 9a, 10, 14, 24, 25a,c Voet, D. and Voet,
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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 <
4.3 Conserved protein domains By comparing the extensive protein databases, it is possible to identify many thousands of conserved domains. For example, within eukaryotes, over 600 domains have been identified with functions related to nuclear, extracellular and signalling proteins. The majority of conserved domains are evolutionarily ancient, with less than 10% being unique to vertebrates.
8.2 Extended radio sources In section 7.5 we studied the spectrum of the synchrotron emission, i.e. how the flux density of radiation depends on the frequency or wavelength of the radio emission. Using radio telescopes such as the VLA (Author(s):
8.1 Continuum spectra Read Section 1.3 of Peterson, up to and including the first two paragraphs of Section 1.3.1 by clicking the link 7.8 Example 2 and questions Example 2 Show that the synchrotron spectrum produced by a power-law distribution of electron energies N(E) dE = N0E−s dE, is described by You may use the approximation that all the power 7.6 Producing synchroton radiation in a laboratory Synchrotron radiation can, of course, be produced in a laboratory by arranging for electrons to be deflected by a magnetic field. Figure 13 shows a beam of synchrotron radiation produced at the European Synchrotron Radiation Facility (Author(s): Learning outcomes By the end of this unit you should be able to: recognise the terminology which is used to describe the properties and behaviour of active galactic nuclei (AGN); manipulate numbers, algebraic symbols and mathematical functions in equations. 1.3.1 Inheritance of colour in maize We can trace the inheritance of characters in animals and plants by following the phenotype from generation to generation, in breeding experiments. We will describe work with maize (Zea mays), alternatively called corn (sweetcorn, or corn on the cob), which occurs throughout the world as an extremely important commercial crop plant, and which is used extensively in genetic research. We can also study the inheritance of characters at the level of the genotype. In this section we will ju 1.2 Like begets like It is possible to follow a character, such as eye colour or hair colour in humans, that is handed down from generation to generation. Such characters are said to be inherited characters (or heritable characters) and are determined by genes. A gene can be considered as a unit of inheritance, which determines a particular character and which is passed on from parent to offspring. Genes maintain the differences between species, such as oak and human, but they also contribute Learning outcomes After studying this unit you should know: the number of chromosomes is characteristic of each species and can vary enormously between species genetics is based on the concept of the gene as the unit of inheritance that sexual reproduction always includes two distinctive processes: the production of gametes, which involves meiosis, and fertilisation. The two processes are accompanied by changes in the chromosome number, from diploid to haploid and fr
Activity 4: General properties of quasars and power-law emission
