Introduction

The cytoskeleton is of fundamental importance to a cell, and the development of different elements of the cytoskeleton were key steps in the evolution of eukaryotic cells. The cytoskeleton controls cell shape and allows cell movement; it is required for many aspects of intracellular trafficking of vesicles and organelles, and it is involved in cell division. Because of its important role in facilitating the movement of vesicles between compartments, but a basic understanding of how the cytosk
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3.8 Activation of transcription factors

We have already come across several examples of signalling pathways leading to activation (or inactivation) of transcription factors, which in turn modulate transcription of sets of genes leading to, for example, programs of differentiation or proliferation. You will also meet several other specific examples in subsequent chapters. For now, we shall examine one particular scenario, namely the activation of immediate early genes by MAP kinases, which illustrates some of the principles and deta
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3.5 Summary of Section 3

  1. Protein domains allow segregation of different functions in the same protein. They can have a binding function, a structural function or a catalytic function.

  2. Binding domains mediate interactions between proteins of related function (such as those in a signalling cascade) and often are important in regulation of activity. Interactions via these binding domains are often dependent on the phosphorylation state of one of the binding partners. Exa
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3.1 Introduction

That proteins contain functionally and physically discrete modules or domains is an important principle, one that will be reinforced as we examine the roles of specific proteins in a variety of different cellular processes.

There are several advantages conferred by multidomain protein architecture:

  1. Creation of catalytic or substrate-binding sites These sites are often formed at the interface between two domains, typically a cleft. Movement
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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
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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
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1.4.3 Protein domains

An important concept in protein structure is that of the protein domain. In many cases, a single polypeptide can be seen to contain two or more physically distinct substructures, known as domains. Often linked by a flexible hinge region, these domains are compact and stable, with a hydrophobic core. Domains fold independently of the rest of the polypeptide, satisfying most of their residue–residue contacts internally. Typically, two or more layers of secondary structural elements eff
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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.

Activity 9: Radio-quiet quasars

0 hours 20 minutes

Read Pe
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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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7.3 Polarization of electromagnetic radiation

So far we have described electromagnetic radiation in terms of its wavelength, frequency and speed. It has another, sometimes important, property: polarization. Figure 10 shows the electric and magnetic field in a plane-polarized electromagnetic wave. In any electromagnetic radiation, the electric an
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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
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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.

Activity 4

Watch ‘A Winning Design’ on the DVD from 30.50–34.12 and write down the behavi
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Learning outcomes

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

  • explain the distinctive biological features of monotremes;

  • distinguish contrasting modes of reproduction in monotremes, marsupials and placental mammals;

  • describe the cellular basis of lactation and explain the benefits of an early diet of milk;

  • explain the significance of mammalian metabolic rate;

  • explain how and why the thermogenic response differs amongst species;


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6.3.3 Photomultiplier tubes and detection circuitry

The visible photons are collected by an array of photomultiplier tubes behind the crystal. These convert each visible photon to an electron and then multiply the number of electrons sufficiently to give a voltage pulse. Because the number of visible photons is proportional to the energy of the incoming gamma ray, the height of the pulse depends on this energy. This gives a method of counting the numbers of gamma photons at different energies that reach the crystal.

A resistive network c
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2.3 Examining Europa's surface

It is all very well speculating about conditions in an ocean below Europa's ice, but what evidence is there that it actually exists? After all, tidal heating might not result in ice melting on a global scale, and current geophysical models of Europa's internal structure (e.g. Figure 14 in Section 1.5) cannot te
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4.3 Hierarchies within groups

Within multimale-multifemale groups of the type portrayed in Figure 7f, complex social relationships exist. These animals are ‘forced together’ to defend resources and to avoid predation, but competition for food and mates is substantially greater in large groups. This internal competition has led to males or female
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6 Promoting science promotion: the move from deficit to dialogue

This unit has tried to distinguish between institutional science outreach events and independent alternatives by recognising some of their characteristics and evaluating the extent to which they fulfil (and even create) a political mandate for PEST (Public Engagement in Science and Technology). Although institutional events sometimes involve the deficit style of ‘top-down’ transmission of facts, the examples provided in this unit suggest that they are increasingly imaginative and unusual.
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2.4 ‘Go Use’ science promotion events

Science shops, created in the Netherlands in the 1960s and now spread throughout Europe, first emerged in the UK in 1988 (at Queen's University, Belfast). They act as a demand-driven link between a university or independent research facility and the community (usually via citizen groups, such as pressure groups, social groups, consumers and residents associations), putting one in touch with the other upon request. They carry out scientific research on practical, scientific problems at the loc
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2.2 Size and shape

The shape of the head is determined mainly by the relative sizes of the jaws and the nose and the back of the skull containing the brain, eyes, ears and, in artiodactyls, the horns or antlers. All these structures may differ greatly between otherwise similar species.

SAQ 7


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3.1 Angular size

Figure 19
Figure 19 A total eclipse of the Sun, revealing the outer part of the Sun's atmosphere, the corona, and the inner part, the chromosphere, which can just be seen
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