1.2 The peptide bond and primary structure of proteins The primary structure of a protein is defined as the sequence of amino acids of which it is composed. This sequence ultimately determines the shape that the protein adopts, according to the spatial limitations on the arrangement of the atoms in the protein, the chemical properties of the component amino acid residues, and the protein's environment. The peptide bonds that link amino acid residues in a polypeptide are formed in a condensation reaction between the acidic carboxyl gr
3.3.1 Phosphatidylinositol 3-kinase (PI 3-kinase) Members of this family of lipid kinases usually have two subunits: one is a catalytic subunit with a lipid kinase domain and the other is a regulatory subunit, which contains two SH2 domains and a SH3 domain (p 85 PI 3-kinase in Figure 13). 2.3.2 Seven-helix transmembrane (7TM) receptors Although in unicellular organisms such as the yeast S. cerevisiae there are only two classes of 7TM receptors, the pheromone and glucose receptors, multicellular organisms have many more, accounting for up to 5% of all genes in C. elegans and 2% of genes in the human and Drosophila genomes. 7TM proteins have been classified into four classes, A, B, C (Table 1). Between them, they can bind a huge range of ligands including simple ions, nucleotides, lipids, steroids, modifi 2.3 Receptor activation Receptors may be activated by conformational change (for example, ion-channel receptors such as nicotinic receptors, and 7TM receptors such as muscarinic receptors and adrenergic receptors), by formation of dimers (such as receptors with intrinsic enzymatic activity and recruiter receptors) or by proteolysis. We shall now consider how each cell surface receptor class described in Author(s): 7.1 Blackbody radiation Interpretation of the light astronomers collect from AGN depends on understanding the physical processes leading to the emission of that light. Because the conditions in the emitting regions of AGN are very different from those on the surface of the Earth, some of these processes may be entirely unfamiliar to you. This subsection begins with a discussion of blackbody radiation, which should be familiar, and covers material which you will need to appreciate Peterson's discussion of AGN. 1 Meet your first active galactic nuclei Figure 1 compares two nearby spiral galaxies of similar distance and type. NGC 5548, on the left, has a brighter nucleus than that of NGC 3277, on the right. This extra emission from the central regions of NGC 5548 is not generated by stars. Instead this light is thought to be ultimately powered by material falling in the gravitational field of 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. 5.2 Alpha decay You have probably met the law of radioactive decay, which says that, given a sample of N0 similar nuclei at time t = 0, the number remaining at time t is N(t) = N0e−λt, where λ, the decay constant for a particular kind of nucleus, determines the rate at which the nuclei decay. The half-life is the time needed for half of any sufficiently large sample to decay. It is related to the de 3.5 Scattering from finite square wells and barriers The procedure used to analyse scattering from a finite square step can also be applied to scattering from finite square wells or barriers, or indeed to any combination of finite square steps, wells and barriers. The general procedure is as follows: Divide the x-axis into the minimum possible number of regions of constant potential energy. Write down the general solution of the relevant time-independent Schrödinger equation in Acknowledgements The organisers of this course are grateful for the financial support provided by the Royal Society, whose generous backing covered all aspects of the course's production and presentation. The material acknowledged below is Proprietary and used under licence (not subject to Creative Commons licence). See terms and conditions. This content is made available under a Derived functions and derivative notation Given the function x(t) that describes some particular motion, you could plot the corresponding position-time graph, measure its gradient at a variety of times to find the instantaneous velocity at those times and then plot the velocity-time graph. If you had some time left, you might go on to measure the gradient of the velocity-time graph at various times, and then plot the acceleration-time graph for the motion. This would effectively complete the description of the motion, b 3.7 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 3.5 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. Examples are 6.4 Taking the image Now watch this video clip of a patients lungs being imaged, called a VQ (ventilation quotient) scan. What are the two different types of acquisitions used called? What radioactive substance is used for each acq 6.1 Introduction Radionuclide imaging is a very valuable way of examining the function of an organ, as opposed to the more structural images obtained by other methods such as X-ray and CT. The basic principles of radionuclide imaging are as follows: a radioactive substance, usually combined with a biologically active compound, is injected into the patient; this targets a particular organ or tissue type; the radiation emitted i 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): 1.3 Unravelling the natures of the large satellites Before the dawn of the space age, relatively little could be discovered about even the large satellites. Their orbits were well known, and from the subtle orbital perturbations caused by neighbouring satellites it was possible to deduce their masses. Measurements of their sizes enabled densities to be calculated to within about 20 per cent of the currently accepted values for the Galilean satellites, and with rather less certainty for the large satellites of the other giant planets. However, 4 Germline gene therapy Now that in vitro fertilization – bringing eggs and sperm together outside the prospective mother's body – is an established technology, the possibility exists that genes could be altered in eggs or sperm, or in a very early embryo. The obvious advantages of germline gene therapy are that the cells are accessible (because they are outside the body), so gene delivery is less of a problem than it tends to be with somatic cells; and the inserted gene (or genes) would be present Introduction Following on from the advances made in diagnosing disorders using genetic testing, this course looks at the possibilities for genetic therapies. Two approaches to gene therapy are discussed: correcting genes involved in causing illness; and using genes to treat disorders. Before closing on a discussion of the issues around 'designer babies' somatic gene therapy and germline gene therapy are discussed. This OpenLearn course provides a sample of Level 1 study in Author(s): 1.3 Beyond visible light During the twentieth century, astronomers extended their capabilities by developing telescopes and detectors that were sensitive to radio waves, microwaves, infrared and ultraviolet radiation, X-rays and gamma rays. All these forms of electromagnetic radiation, along with visible light, are emitted by the Sun.
Activity 14
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