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2.4 Obesity – an evolutionary perspective

If you were now to take a broader biological approach to the data discussed in the previous section you might still be puzzled. Excess body weight leads to a variety of diseases, including diabetes, osteoarthritis and so on – surely this must reduce overall biological fitness.

SAQ 21

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7.6 Questions

Question 15

Suppose that a galaxy has emission lines in its optical spectrum. A line of wavelength 654.3 nm is broadened by 2.0 nm. Estimate the velocity dispersion of the gas giving rise to the broadened spectral line. Is it likely to
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7.5 Outstanding issues

  • Evidence from rotation studies shows that some AGNs do indeed contain compact, supermassive objects within them, though there is no direct evidence that these are black holes.

  • Quasars were most abundant at redshifts of 2–3 and have been declining in number for the last 10 billion years.

  • It seems probable that AGNs fade with time as the supply of accreting material is used up. There is speculation that AGNs may be rejuvenat
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Introduction

There are a wide range of different interactions between ‘science and the public’. Examples range from visiting a museum, or indulging in a science-related hobby, to reading a newspaper article about a breakthrough in the technique of therapeutic cloning, to attending a protest meeting about plans to build a waste disposal unit near to a residential area. Some such interactions are largely one-way; being a member of the audience for a ‘go-hear’ lecture, visiting a museum or‘‘liste
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Introduction

Energy from sources other than fossil or nuclear fuels is to a large extent free of the concerns about environmental effects and renewability that characterise those two sources. Each alternative source supplies energy continually, whether or not we use it. Many alternative sources of energy have been used in simple ways for millennia, e.g. wind and water mills, sails, wood burning – but only in the last two centuries has their potential begun to be exploited on an industrial scale. Except
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Learning outcomes

By the end of this unit you should be able to:

  • using information from wells, the topography of the ground and a water table contour map, 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 make g
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3.4 Second messengers

In the previous section, we have discussed the principles of second messengers (Section 1.5) and, in particular, those produced by PLC (IP3 and DAG) and PI3 kinase (PI(3,4)P2 and PI(3,4,5)P3). We shall now consider the roles and mechanisms of action of the other chief mediators, which are Ca2+ ions, cAMP and cGMP
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3.3.2 Phospholipase C (PLC)

Members of this family of enzymes contain two catalytic domains and several protein binding domains (Figure 13). The PH domain can temporarily tether phospholipase C to the membrane by attachment mainly to PI(3,4)P2.

We shall discuss two main isoforms of PLC: PLC-β, which is activated by a subset of trimeric G proteins (Gαq an
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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).

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2.6 Summary

  1. Receptors comprise a limited number of structural motifs, which determine binding affinity and specificity of receptor–ligand complexes. Some ligands bind to several receptors and some receptors bind to several ligands.

  2. Acetylcholine is a good example of a ligand with two structurally different kinds of receptor. Nicotinic receptors are ion channels, which are found predominantly in skeletal muscle, and are stimulated by nicotine. Nicotinic
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Learning outcomes

This unit will:

  • encourage you to engage with the natural environment around you

  • help you to take part in observing nature yourself

  • provide an opportunity to communicate with a wider community

  • encourage you to to use ICT to record your findings.


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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,
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3.2 QSO spectra

It only became apparent that these quasi-stellar objects were not stars when their spectra were examined. At first astronomers could not interpret their spectra because the spectral lines did not appear at appropriate wavelengths for atoms of any known chemical element. The spectrum shown in Figure 4 provided the
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3.7 Insulin

Insulin is a hormone produced by the pancreas. It has many actions, but is particularly important in keeping the blood glucose level normal.

Question: How does
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3 Computed tomography

The aim of computed tomography (CT) is to produce an image of a slice of the body. (The Greek word ‘tomos’ means slice.) This is achieved by rotating a thin, fan-shaped beam of X-rays around the patient and measuring the intensity on the opposite side of the patient with a very large number of detectors.

Figure 6
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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
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Learning outcomes

By the end of this unit you should be able to:

  • discuss processes upon and within, and internal structure of, differentiated icy bodies (primarily large satellites) in comparison with the terrestrial planets;

  • describe the conditions that may be required to originate and foster life in an icy body and discuss the likelihood of their having occurred;

  • recognise the moral and ethical issues of landing spacecraft on potential life-bearing worlds and appre
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3.2 Colour vision

DA stresses that colour vision is very important in primates, not only because colour is used ‘in sexual displays’ such as advertising a female's receptiveness to mating [p. 275], but also to identify ripe fruit [p.247] and to select nutritious leaves [p. 255]. This section discusses these points in more detail and explains how the visual system in primates is able to detect colour.

White light is composed of light of different wavelengths, from 300–800 nanometres (nm); 1 nm is on
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References

Durant, J., Bauer, M., Gaskell, G., Midden, C., Liakopoulos, M. and Scholten, L. (2000) ‘Two cultures of public understanding of science andtechnology in Europe’ in Dierkes, M. and Von Grote, C. (eds) Between Understanding and Trust: the Public, Science and Technology, Amsterdam: Harwood Academic Publishers.
Eurobarometer
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4.3 Phenotypic changes that appeared without being selected

As well as these behavioural changes, many of the selected foxes had unusual white markings (Figures 13c and d). The first colour change that the Russian investigators noted in their foxes was a white ‘star’ on the forehead similar to that of other domesticated mammals (Author(s): The Open University

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