2.2 Using A. tumefaciens to genetically modify plant cells

Genetic engineers have capitalised on the fact that part of the DNA from the Ti plasmid of A. tumefaciens is integrated into the plant genome during the infection process. Ti plasmids can be isolated and a foreign gene spliced in at an appropriate point, making it possible to transfer the novel gene into the plant.

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2.1 Crown gall disease: genetic engineering in nature

A. tumefaciens causes crown gall disease in a wide range of dicotyledonous plants. (Dicotyledonous plants, are also known as dicots, have broad leaves with branching veins. An example would be a broad leaved tree like an oak. Narrow leaved plants with parallel grains such as grasses are known as monocotyledonous plant or monocots.) The infection normally occurs at the site of a wound in the plant. The disease gains its name from the large tumour-like swellings, or galls, that o
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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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Acknowledgements

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

The content acknowledged below is Proprietary and used under licence (not subject to Creative Commons licence). See Terms and Conditions.

Figures

Figure 4 BP (2
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3 Summary

Hydropower was the earliest means of commercial electricity generation, and currently dominates alternative electricity supply. However, its global capacity for large-scale exploitation is less than six times that currently installed.

Growth of hydropower is slow and its contribution to global electricity supply is falling. Both are due to economic factors, the slow pace of large-scale project construction, the remoteness of high-potential sites, and increasing resistance to the social
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1 Hydropower

Hydroelectric energy is ultimately solar energy converted through evaporation of water, movement of air masses and precipitation to gravitational potential energy and then to the kinetic energy of water flowing down a slope. That energy was harnessed for centuries through the use of water wheels to drive mills, forges and textile works, before being supplanted by coal-fired steam energy. Electricity generation using water turbines, although first centred on constricted streams, has increasing
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Learning outcomes

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

  • explain the principles that underlie the ability of hydropower to deliver useable energy;

  • outline the technologies that are used to harness hydropower;

  • discuss the positive and negative aspects of hydropower in relation to natural and human aspects of the environment.


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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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4.3 Iron storage

In humans, iron is stored mainly in the bone marrow, spleen and liver. About 10 per cent of all the iron in the body is in storage. Two proteins are involved in iron storage; these are called ferritin and haemosiderin (they also occur in other organisms). We shall only study the better characterised (and simpler!) ferritin.

Each ferritin molecule can store iron up to about 20 per cent of its total mass. This is a very high percentage, considering that less than 0.2 per cen
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4.2 Iron transport

It is obvious that iron must be transported around the human body. Firstly, it must be transported from the food in the gut to the places where it is required. Mostly, iron is required in the bone marrow, where red blood cells are formed. Red blood cells have a finite lifetime of about only four months, and old cells are destroyed, usually in the spleen. Iron from the destruction of these cells is then transported from the spleen back to the bone marrow to be recycled.

Iron cannot be tr
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3.2 Removal of iron

Before leaving enterobactin to look at iron transport and storage in humans, it is worth asking the question: how does E. coli remove the iron from such a stable complex as the iron(III)–enterobactin once it has been absorbed?

The answer to this question can be found if we look back to reaction 38. The rigid, three-dimensional structure of the triserine ring of enterobactin is the main reason why enterobactin is such an effective ligand. If the structure of the ring is destroye
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2.1 The problems of iron uptake

Iron has a high natural abundance. It is the second most abundant metallic element by mass in the Earth's crust (7.1 per cent).

Activity 1

What are the main oxidation states of iron?


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Introduction

In this unit we will see that, despite having a high natural abundance, iron is in very short supply because of the insolubility of its oxides and hydroxides. A result of this is that organisms have developed methods for the uptake, transport and storage of iron. For example, iron storage in mammals, including humans, is achieved by ferritin, which stores iron as a hydrated iron(III) oxide – an example of biomineralisation.

This unit is from our archive and is an adapted extract from
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References

Green, S. (1971) The Curious History of Contraception, Ebury press, London.

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3.9 Questions for Unit

Question 1 (Objective 2)

Figure 19 is a graph showing how the viscosity (thickness and stickiness) of a woman's cervical mucus changes with time. Day 0 is the start of her menstrual period.


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3.7 Selecting the sex of a child

Once a pregnancy has been established, many couples are anxious to know the sex of their unborn baby. The reasons for this are many, ranging from the prosaic (will the baby be able to use its brother's or sister's old clothes) to the deeply religious (as described for Hindus in Section 2). In many communities there is so much social pressure on mothers to produce the ‘right’ sex (usually male) that infanticide of the ‘wrong’ sex is widely practised. Because this is illegal in most soc
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3.5 A new life

There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’, i.e. when a woman could feel her fetus moving inside her. However, both these opinions suffer from an underlying falsehood: that life ‘begins’ at all. Life is a continuum; gametes are produced by living parents, and fuse to produce new living individuals, but unfused gametes are n
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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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3.4.2 Compaction and adhesion

Around the time of the 8- to 16-cell division, the conceptus undergoes a morphological (shape) change, called compaction, in which the cells fatten on each other, and the outlines of individual cells become hard to distinguish. This stage, sometimes referred to as a morula, from the Greek word for mulberry, is shown in Figure 17i. At this stage it is hard to see individual cells; in fact, unless the cells are separated by various laboratory treatments, it is not possible to see the two
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