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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.


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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 <
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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.


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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
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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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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
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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.

Question 12

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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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1.7.2 End-of-unit questions

Question 25

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
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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
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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
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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
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1.6.1 Describing uniformly accelerated motion

An important special case of non-uniform motion along a line is that which arises when an object is subjected to constant acceleration. This kind of motion is called uniformly accelerated motion. An object falling under gravity near to the surface of the Earth, such as the apple of Figure 24, provides
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1.4.7 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

<
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Learning outcomes

After studying this unit you should be able to:

  • explain the meaning of all the newly defined (emboldened) terms introduced in this unit;

  • draw, analyse and interpret position–time, displacement–time, velocity–time and acceleration–time graphs. Where appropriate, you should also be able to relate those graphs one to another and to the functions or equations that describe them, particularly in the case of straight-line graphs;

  • find the derivati
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2.2.2 Collimator

The dimensions of the emerging X-ray beam can be altered by the collimator. This helps to ensure that only the region of interest is exposed to the X-rays.


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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

T
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3.2 Angular size, actual size and distance

The angular size of an object is determined uniquely by its actual size and its distance from the observer. For an object of fixed size, the larger the distance, the smaller the angular size. For objects at a fixed distance, the larger the actual size of an object, the larger its angular size. For objects with small angular sizes, such as typical astronomical objects, the precise relationship between angular size, actual size and distance is well approximated by th
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4.1 The grizzly bear

There are three activities in Section 4, asking you to summarise information in the form of lists. In the first two, the answers are given but in the third, about the diet of the giant panda, they are not. You are asked to tick off the points in your list as you read on through the section. As you gain more stu
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3 Is specialisation always advantageous?

Specialisation generally implies the possession of adaptations that make animals particularly effective or efficient in one or more aspects of their lives. In many of the examples used in other units in this series, mammals are likely to possess adaptations related to the acquisition and/or processing of food.

Que
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