1.5 Quaternary structure This level of protein structure applies only to those proteins that consist of more than one polypeptide chain, termed subunits. In such proteins, sometimes referred to as multisubunit proteins, the same kinds of non-covalent interaction that stabilise the folded polypeptides also specify the assembly of complexes of subunits. Quaternary structure refers to the way in which the subunits of such proteins are assembled in the finished protein. Multisubunit proteins can have a numbe
1.3.3 Reverse turns and loops In compact globular proteins, a polypeptide often makes a sharp turn called a reverse turn. For instance, these turns often link adjacent strands in antiparallel β pleated sheet (as represented in Figure 12a). Also known as β bends, reverse turns involve four amino acid residues with a hydrogen bond between the C=O group of the f
8.3 Line spectra: ions and spectral lines For obvious reasons optical astronomy developed earlier than radio and X-ray astronomy, and astronomers are able to learn many things from analysis of optical emission. Just as in the radio band, optical pictures, i.e. the spatial distribution of emission, can be informative. Even when a source is not spatially resolved, astronomers can still deduce some information about what it might look like close-up. These ‘visualizations’ of what is happening in a particular source result from analy
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
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 acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged
5.1 Ruminants The earliest ruminant was probably an ancestor of the present-day chevrotain. The chevrotain skeleton appears to have remained virtually unchanged for the past 30 million years and, although there are now only four species confined to the jungles of Africa and Southeast Asia, they once had a worldwide distribution. So, chevrotains are placed in the suborder Ruminantia within the order Artiodactyla, to which other deer, antelopes, cattle, sheep and goats also belong. A second suborder, the Tyl
1 The herbivores As you work through this unit you will come across boxes, like this one, which give you advice about the study skills that you will be developing as you progress through the unit. To avoid breaking up the flow of the text, they will usually appear at the start or end of the sections. As well as the unit t 3.3 Variation Fossil rodents are first found in rocks that date from around 65 million years ago (from the Eocene) and are thought to have evolved from insectivore/omnivore-type mammals that lived 100 million years ago (in the Cretaceous period). To say that they evolved from simply means that there probably is a direct line of descent but that the descendants have changed from their forebears. One of the most significant ways that evolutionary change can be brought about is by a process known as na 2.1 Overview In this section, you will meet some new units, the units in which energy is measured. Nowadays, there are internationally agreed units (called SI units) that are often used in combination with a prefix to show the scale of the measurement. The SI unit for energy is the joule (pronounced ‘jool’, and with the 3.3 Moles In this section, you will meet one of the ways in which scientists are very precise about the way that they use ordinary words. Spot the difference between ‘The golden mole evolved webbed hind feet so that it can shovel sand backwards as it moves forwards’ and ‘The golden mole evolved webbed hind feet and Learning outcomes By the end of this unit you should be able to: describe the lifestyle of a variety of insect eaters, from four orders; give examples of adaptations linked to feeding in insect eaters; explain the limited extent to which insectivores can be regarded as ‘primitive’; characterise typical adult mammalian dentition and understand dental formulae; recognise teleology and write down accounts of evolution that do not assume 3.5.2 Mechanical force directly opens and closes transduction channels It is believed that tip links aid in causing ‘channels’ to open and close near the top of the hair cell (Figure 16). Tip links are filamentous connections between two stereocilia. Each tip link is a fine fibre obliquely joining the distal end of one stereocilium to the side of the longest adjacent process. It is thought that each l 4 Suggestions for further reading If you wish to pursue some of the topics discussed in this unit in greater detail you might like to start with one or another of the following works.
General John D. Barrow (1988), The World Within the World, Oxford. Richard P. Feynman (1992), The Character of Physical Law, Penguin Books. Brian Greene (1999), The Elegant Universe, W. W. Norton. Werner Heisenberg (1990), Physics and Philosophy, Penguin Books. Jan Hilgevoor 3 Appendix: Some highlights of physics 2.5.2 Quantum fields and unification From its inception, quantum physics was concerned not just with particles such as electrons, but also with light and other forms of electromagnetic radiation. In 1900 Planck discovered the quantum in the transfer of energy from matter to radiation, and in 1905, Einstein's explanation of the photoelectric effect assumed that the transfer of energy from radiation to matter occurred in a similarly quantised fashion. It is therefore hardly surprising that the development of quantum mechanics was 2.5 The uncertain Universe Despite the impact of relativity, the greatest source of change in the scientific world-view in the twentieth century has undoubtedly been the development of quantum physics. This is the branch of physics that is mainly concerned with microscopic entities such as atoms and molecules, and their constituents. It is by far the most quantitatively accurate part of science, routinely providing predictions that are correct to just a few parts in a million. Quantum physics is also of enormous Faraday and Maxwell 2.3.3 Statistical mechanics You saw earlier that very strong claims were made for Newtonian mechanics. Many regarded it as a basic framework that would underlie all scientific explanations. It is therefore natural to ask about the relationship between Newtonian mechanics and thermodynamics: Do they contradict one another? Are they separate aspects of the truth? Can thermodynamics be derived from Newtonian mechanics? These are no 2.3.1 Thermodynamics and entropy The first half of the nineteenth century was a period of great economic and industrial growth. The steam engine, invented in the previous century, was becoming increasingly common in locomotives, mines and factories; power was becoming available on demand. A major priority for engineers was to produce more efficient engines, in order to deliver more useful power for less expenditure on fuel. Thermodynamics emerged as a study of the basic principles determining energy flows and the effi 2.3 The irreversible Universe ‘Science owes more to the steam engine than the steam engine owes to Science.’ L.J. Henderson (1917) From the time of Newton until the end of the nineteenth century the development of physics consisted essentially of the refinement and extension of the mechanical view of the Universe. There were many stages in this process but one of the most interesting came towards its end with the re
c. 624 BC
Birth of Thales of Miletus: traditionally ‘the first physicist’.
384 BC
Birth of Aristotle: author of Physics.
1543
Nicolaus Copernicus' De Revolutionibus Orbium Celestium.
1600
William Gilbert's De Magnete describing the behaviour of
Michael Faraday (1791–1867)
