7.3 The central engine An object that fluctuates in brightness on a timescale Δt can have a radius no greater than R ∼ cΔt. The point-like nature of AGNs and their rapid variability imply that the emitting region is smaller than the size of the Solar System. The central engine of a typical AGN is believed to contain a supermassive black hole of mass ∼108M ⊙ and Schwarzschild radius
Active galaxies
Figure 6 shows a schematic optical spectrum of an active galaxy. It is immediately apparent that the emission lines are stronger and broader than in the spectrum of a normal galaxy shown in Author(s):
5 How might dialogue move on from GM Nation? There is a widespread optimism that ‘lessons have been learnt from the GM Nation? Debate’ – indeed the government's response to the exercise was couched in just those terms (DEFRA, 2004). One concern has been touched on already – many felt that the debate took place too late, on a rushed timetable, at a time in the controversy when the debate had become highly polarised and divisive ‘pro’ or ‘anti’ stances already embedded. This late in the day, questions for public discussion
3.4 Consensus conference on plant biotechnology The first UKNCC (at Regent's College) was hosted by the Science Museum and funded by the Biotechnology and Biological Sciences Research Council (BBSRC). The conference was based on a procedural model developed by the Danish Board of Technology. In Denmark, consensus conferences are held regularly and can be seen to have had unequivocal effects on policy making. Indeed, in a number of instances, Parliament has explicitly incorporated lay-panel recommendations in legislation. For example, lay-p
References
3.2 Uranium occurrence and ore deposits In igneous rocks, uranium is more abundant in granites (~3.5 ppm) than in basalts (~1 ppm). The large size of the uranium atom prevents it from easily entering the structures of common rock-forming minerals, so it is an incompatible element that tends to remain in magmas until a late stage of crystallisation, when it enters minor minerals, or even the uranium oxide, uraninite (UO2). In suitable circumstances, following fractional crystallisation of uranium-rich granitic magm
Acknowledgements The content acknowledged below is Proprietary (see terms and conditions). this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence. Grateful thanks is made to the pupils and staff of: The Henley College, Oxon; Langtree School, Woodcote, Oxon and The Hill Primary School, E
Acknowledgements Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 LicenceSee Terms and Conditions Figure: 1 Copyright Â
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2.1 Introduction Every receptor has to be able to recognize its particular ligand in a specific manner, and become activated by it in such a way that it transmits the signal to the cell. We shall deal with receptor specificity and activation mechanisms. Then we shall see how the same principles of specificity and activation also apply to intracellular receptors.
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 Studying protein–protein interactions The investigation of protein–protein interactions is a very important aspect of understanding proteins. Identifying binding partners can give insight into a protein's function. Many different methods and technologies have been developed to identify and characterise interactions between proteins, a few of which are described here.
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
1.4.4 Covalent cross-linkages stabilise protein structure Proteins that are secreted by the cell, or are attached to the extracellular surface of the plasma membrane, can be subject to more extreme conditions than those experienced by intracellular proteins. Often, covalent cross-linkages stabilise these proteins by connecting specific amino acids within a polypeptide or between polypeptide chains in multisubunit proteins (see below). Typically such a linkage will be a covalent sulfur–sulfur bond which forms between the –SH groups of two cystein
6.3 Risk Risk is a difficult concept. Most of what we do in life involves making choices and taking risks. Sometimes the risks are small, and sometimes they are large. It can be difficult sometimes to know what the risk of doing something is. Past experience can also influence the way we think about risk. If one was knocked over by a car crossing the road, then even though the risk of it happening again is small we may remain worried and concerned about crossing the road. How you explain risk is
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. 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 1.7.2 End-of-unit questions
Table 8 shows the atmospheric pressure P in pascals (Pa) at various heights h above the Earth's surface. Plot a graph to give a visual representation of the data in the table. Be careful to label your axes co 1.7.1 Unit summary 1. A coordinate system provides a systematic means of specifying the position of a particle. A system in one dimension involves choosing an origin and a positive direction in which values of the position coordinate increase. Values of the position coordinate are positive or negative numbers multiplied by an appropriate unit of length, usually the SI unit of length, the metre (m). 2. The movement of a particle along a line can be described graphically by plotting values of the particle's 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 1.6.2 The equations of uniformly accelerated motion Equations 22, 23 and 24 provide a complete description of uniformly accelerated motion. By combining them appropriately, it is possible to solve a wide class of problems concerning the kinematics of uniformly accelerated motion. Nonetheless, those particular equations are not always the best starting point for the most common problems. For example, it is often the case that we want to know the displacement from the initial position after some specified period of constant acceleration, rather
Question 12
Activity 4
Question 25
