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Reactive oxygen species

The metabolism that occurs in every cell and is associated with the basic requirements of physiology inevitably leads to the production of reactive intermediates, many of which are capable of reacting with DNA or free dNTPs, which could subsequently be incorporated during synthesis. One particular group of such molecules are called reactive oxygen species (ROS). The essential feature of ROS is the presence of an unpaired electron on an oxygen atom in the molecule, which enables the ROS to rea
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2.3 Global power demand

In Section 2.2 we calculated a value of 14.3 TW for the average global requirement for primary power in 2002
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6.2 Do supermassive black holes really exist?

One outstanding feature of the black-hole model is that the black hole must be supermassive. Can one at least detect the presence of a massive central object?

  • How might a massive central object be detected using information from galactic rotation curves?

  • By measuring rotation speeds near the nucleus of the galaxy. The faster the rotation speeds, the greater the enclosed mass.

So the answer is yes. In NGC 4151
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Acknowledgements

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9.1 Field-work risk assessment

Field-work covers a wide spectrum of outdoor activities and takes place in almost every environment present both in the UK and abroad. It is acknowledged that there is an element of risk in much of this work. The Health and Safety at Work Act recognises that risk is inherent in some occupations and seeks to ensure that systems of work are in place to reduce risks to an acceptable level.

There has been increasing concern about the safety of field trips in the light of recent court cases
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7.6 Personal protective equipment

Figure 12
Figure 12 Personal protective equipment (PPE) for working with highly corrosive liquids

In most laboratories, laboratory coats and
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4.3 Golden Rice in the public domain

In January 2000, the successful experiments were announced in a paper published in the American journal Science. This, in itself, is significant. Generally, work on genetic manipulation would be published in one of a number of more specialist journals. Publication in a journal like Science indicates that this was important work, likely to be of interest to a wider audience. In its ‘Notes for Authors’, the journal states that ‘Priority is given to papers that reveal novel c
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1 Genetic manipulation of plants and GM crops: an introduction

In this unit we will consider the genetic manipulation of plants, and the production of GM crops. A great deal has been written about the science of GM crops and the controversial issues surrounding their introduction around the world. In the study time available, we will focus on a small number of selected issues.

In this unit you'll have the opportunity to learn more about the science that has been used to engineer a range of GM crops, and examine both the science and social concerns
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Learning outcomes

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

  • understand more about the science that underlies the development of genetically modified organisms and in particular how gene transfer is brought about;

  • know something of the potential benefits and uncertainties associated with gene transfer and the high levels of technical ingenuity involved;

  • be better able to understand the science that underpins the development of Golden Rice and understand why the u
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3.1 How do organisms take up iron?

Nearly all organisms are able to take up iron. However, only a handful of organisms have had their iron-uptake chemistry studied. The organism that has received most attention (other than human) is a single-cell, prokaryotic bacterium (found in the human large intestine and elsewhere), called Escherichia coli (abbreviated to E.coli), a high-resolution image of which is shown in Author(s): The Open University

3.4.3 Summary of Section 6

  1. For the first week after fertilization, the conceptus (early embryo) foats freely in the female reproductive tract, obtaining some of its nutrients from the fuid in which it is bathed.

  2. The fertilized egg begins a series of divisions to give 2, then 4, then 8 undifferentiated cells. There is no net cell growth, so each generation of cells is smaller than the last.

  3. The 8- to 16-cell division is different, and important. Each
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Introduction

We have seen that where precipitation reaches the ground, some runs off the surface into streams and rivers and some of it infiltrates, passing through the soil. Water that reaches the water table to become groundwater may eventually re-emerge at the surface as springs where the water table intersects the surface. Almost all streams and rivers have springs or seepages as their ultimate source, or are fed by them at various points along their courses.

This unit is from our archive and is
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1.3.4 Coil conformations

In addition to the repetitive helical and pleated sheet structures, there are other non-repetitive, and therefore more varied, elements of secondary structure called coil conformations. The lack of regular repetitive order in coil conformations does not, however, mean that these structures are disordered or unstable. In fact, it is clear from X-ray diffraction studies of proteins that these regions are consistent in the conformation that they adopt.

Regions of disorder do exist,
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Acknowledgements

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

The content acknowl
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1.5.6 Velocity and acceleration as derivatives

Recalling that the instantaneous velocity of a particle at time t is given by the gradient of its position–time graph at that time, we can now use the terminology of functions and derivatives to say that the velocity of the particle is given by the derivative of its position function. In terms of symbols:

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1.5.4 Functions and the function notation

In Figure 25, the position x of the car depends on the time t. The graph associates a particular value of x with each value of t over the plotted range. In other circumstances we might know an equation that associates a value of x with each value of t, as in the case of the equation x = At + B that we discussed in Section 3. You can invent countless other ways in which x depends on t: for instance x = 
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2.6 How can we find out more about Europa?

There are currently no scheduled missions to Jupiter's moons, since NASA's Jupiter Icy Moons Orbiter (JIMO) was cancelled in 2005, but Europa remains a high priority target for both NASA and ESA, so a mission with simlar objectives to JIMO seems likely by about 2020. On arrival at Jupiter, JIMO would have gone into orbit first round Callisto, then Ganymede and finally Europa.

The main objectives of JIMO at Europa would have been to:

  1. Determine the
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3.4 Stereoscopic vision

DA explains that ancestral monkeys had to ‘decide whether a branch was within reach of a stretch or a jump – or beyond either’ [p.248]. Individuals that were able to judge distances between themselves and branches more accurately had a competitive edge over other individuals, which led to the development in primates of stereoscopic vision. Stereoscopic vision evolved convergently in carnivores that judge distances to capture fast-moving prey.

The field of view of a single eye is t
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