1.6 Fibrous proteins Most of the proteins described so far have been globular proteins. There are, however, some distinctive features that characterise fibrous proteins and we present here a general overview of these. Elongated fibrous proteins frequently play a structural role in the cell. They do not readily crystallise but tend to aggregate along their long axis to form fibres. X-ray diffraction studies of these fibres, in contrast to analysis of protein crystals, provides only very limited information on the
Introduction Proteins are the ‘doers’ of the cell. They are huge in number and variety and diverse in structure and function, serving as both the structural building blocks and the functional machinery of the cell. Just about every process in every cell requires specific proteins. Let us begin by listing some of the basic cellular processes and the role that proteins play. Chemical catalysis Enzymes, which are responsible for catalysing biological
8.7 Luminosity functions Samples of galaxies can be biased due to the flux limit of the sample that is observed. This is the so called Malmquist bias. Read Pe 7.9 Compton scattering Electromagnetic radiation interacts strongly with electrons. If a photon encounters an electron, there is a high probability that a scattering interaction will occur. In the low-energy non-relativistic regime, i.e. where h 7.5 Emission from spiralling electrons: synchrotron radiation In the very first reading (Activity 1) we encountered the term ‘non-thermal’ describing the spectrum of light emitted from AGN. In this subsection we will learn more about the most important type of non-thermal radiation: synchrotron emission. When a charged particle moves in the presence of a magnetic field it experiences a Lorentz force, which produces an acceleration whose direction is perpendicular to both the magnetic field line and the velocity of the particle, 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 5 The Scopes monkey trial This section was written by Gary Slapper. In 2007, Professor Michael Reiss, a Church of England priest and the head of science at London's Institute of Education, said that it is becoming more difficult to teach evolution in schools because of the spread of creationism. Similar debate has long been burning in the United States. Also in 2007, a creationist museum opened near Cincinnati, where children in animal skins play amid model dinosaurs, suggesting they once coexisted and th 1.6 Summary The number of chromosomes is characteristic of each species and can vary enormously between species. 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 from haploid to diploid, respectively. Genetics is based on the concept of the gene as the unit of inheritance. A particular phenotypic character is det 2 The biology of prions The increasing interest in kuru during the 1950s and 1960s had the effect of stimulating research into TSEs in humans and other animals. Summarise, in general terms, the possible causes of disease in animals. Learning outcomes After studying this unit you will know more about: the way that prion molecules cause diseases such as BSE and vCJD, and how the key discoveries about prions were made; the patterns of BSE and vCJD in populations, and how this information is used to predict the number of cases there may be in future (and to assess the accuracy and precision of such predictions); how science can make important contributions to managing episodes such as BSE/vCJD, and 6 Thermoregulation and mammalian fur A coat of profuse mammalian body hair is commonly called fur. Fur provides insulation, which is a property that one first thinks of as useful for mammals to help retain body heat. Fur is a unique and fundamental feature of mammals, though not all living species possess it. 3 Reproduction in marsupials The study of mammals requires you to deal with measurements, which we call numerical ‘data’, and you will get practice with compiling and analysing data if you work through all the units in this series. We assume only that you can add, subtract, multiply and divide. In this section, we ask you to use units 1.5.2 Instantaneous acceleration The procedure of Question 15 for determining the instantaneous velocity of the car can be carried out for a whole set of different times and the resulting values of
vx
can be plotted against t to form a graph. This has been done in Figure 28, which shows how the velocity varies with time. At time t = 0 s, the car has zero velocity because it starts from rest. At later times, the velocity is positive because the car moves in the direction of in 1.4.5 Velocity–time and speed–time graphs Just as we may plot the position–time graph or the displacement–time graph of a particular motion, so we may plot a velocity–time graph for that motion. By convention, velocity is plotted on the vertical axis (since velocity is the dependent variable) and time (the independent variable) is plotted on the horizontal axis. In the special case of uniform motion, the velocity–time graph takes a particularly simple form – it is just a horizontal line, i.e. the gradient is zero. Ex 1.1 The description of motion The concepts that have been developed to allow the description of motion – concepts such as speed, velocity and acceleration – are now so much a part of everyday language that we rarely think about them. Just consider the number of times each day you have to describe some aspect of motion or understand an instruction about motion; obey a speed limit or work out a journey time. We may take the description of motion for granted, but the concepts involved are so fundamen Acknowledgements This extract is taken from S809 © 2005 The Open University. All written material contained within this unit originated at the Open University. 6.3.1 Collimator Without a collimator, gamma rays from all directions would be collected by the crystal and no useful image could be obtained. Gamma rays cannot be focused by a lens but a collimator consisting of a series of holes in a lead plate can be used to select the direction of the rays falling on the crystal. Most collimators in use today are parallel hole collimators. A parallel hole collimator is shown schematically in Author(s): 2.6 How can we find out more about Europa? There are currently no scheduled missions to Jupiter's moons, since NASA's Jupiter Icy Moons Orbiter (JIMO) was cancelled in 2005, but Europa remains a high priority target for both NASA and ESA, so a mission with simlar objectives to JIMO seems likely by about 2020. On arrival at Jupiter, JIMO would have gone into orbit first round Callisto, then Ganymede and finally Europa. The main objectives of JIMO at Europa would have been to: Determine the 2.4 How thick is Europa's ice? You learned in Section 1.4 that geophysical data show the ‘icy’ outer part of Europa to be about 100 km thick, but that the information is inadequate to distinguish between the extreme possibilities of solid ice all the way down to the bedrock and a floating sheet of ice supported above a liquid ocean (Author(s): 2.3.2 The crater Pwyll You might also have noted that there are no obvious impact craters visible in Figure 16 (see Section 2.3.1). In fact there are a few. One is a bright spot, 15 km in diameter, surrounded by a dark halo of ejecta that occurs 10 mm from the top edge and 65 mm from the left-hand edge of the figure. Another is a s
Activity 9: Radio-quiet quasars
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Question 12
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