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4.4.1 Phosphorus (P)

Like calcium, phosphorus is important in the structure of bones and teeth. It is vital in the body as part of the molecules ATP and DNA, and is also a component of phospholipids, lipoproteins and many other proteins too. Phosphorus can occur, combined with oxygen, in phosphate ions and in this form it plays an important role in switching on and off metabolic pathways in cells. Phosphorus is widely available in the diet, from both plant and animal sources, such as meat, fish, eggs and dairy pr
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Learning outcomes

After studying this Unit you should know:

  • that certain minerals are required in the body and that some minerals form essential structural components of tissues;

  • that sodium, potassium, calcium and chloride ions are important in maintaining the correct composition of cells and of the tissue fluids around them (homeostasis);

  • that some minerals are essential components of important molecules such as hormones and enzymes;

  • that the correct
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Acknowledgements

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All other materials included in this unit are derived from content originated at the Open University.

1. Join the 200,000 studen
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9 Summary

In this unit you have found out that:

  • The sensation of pain is caused by the release of a chemical (prostaglandin) that stimulates the nerve endings and sends an electrical message to the brain.

  • Pain can be reduced if the formation of prostaglandin can be inhibited.

  • Prostaglandin is formed, from arachidonic acid, in a cavity in the active site of the enzyme cyclooxygenase (COX).

  • Geometrical isomerism
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1.8 Enter aspirin!

Aspirin is able to release part of its ester group (Figure 15) in a hydrolysis reaction. Look again at the structure of aspirin, 2.8, and identify this group on the molecule. It is known as an acetyl group and accounts for aspirin also being called acetylsalicylic acid. The acetyl group on aspirin is fairly easily removed and can be available for forming another ester with an —OH group on another molecule; in this case, part of the structure that makes up the inside of the cavi
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under licence.

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

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Chaserpaul

All other materials included in this unit are derived from content originated at the Open University.
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1 1.2 How DNA is replicated

Cell division involving the nuclear division of mitosis produces two progeny cells, which contain identical genetic material, which is also identical with that of the original parent cell. This is how a fertilized egg grows into an adult many-celled organism. For one cell to become two new ones with identical genetic material, the DNA in each chromosome must undergo a process in which an identical copy is made.

As noted above, Watson and Crick postulated that DNA base-pairing provides a
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Learning outcomes

After studying this unit you should understand:

  • the basic composition and structure of DNA;

  • what is meant by complementary DNA base pairing;

  • how base pairing allows a mechanism for DNA replication;

  • the number of DNA molecules within a chromosome.


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5 Where does transcription occur in the cell?

Up to now we have described the processes of transcription without considering where each occurs within the cell.

SAQ 5

Given that transcription — the production of mRNA — requires a DNA template, where do you think this process occur
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Introduction

This unit explores how information contained in DNA is used, explaining the flow of information from DNA to RNA to protein. Also introduced are the concepts of transcription (as occurs between DNA and RNA) and translation.

This unit is an adapted extract from the course Human genetics and health issues (SK195)


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1.1.5 Late-onset single-gene disorders

An individual might know that a late-onset disease such as Huntington's disease (HD) is present in their immediate family and that they might have inherited the disease gene(s). The problems of genetic testing for HD revolve around the fact that it is pre-symptomatic.

One dilemma is the long delay between testing positive and developing the clinical symptoms of the disorder in middle age. Is it better not to know and live in hope, or as one victim cried ‘get it over, I'm so tir
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1.1.4 Genetic testing of adults

Huntington's disease is a good example of a late-onset disorder because it is fatal, non-treatable, relatively frequent and has a strong genetic element that can be tested for. There are others that fall into a similar category, i.e. mainly relate to a single gene, such as adult polycystic kidney disease. The issues surrounding late-onset multifactorial diseases, such as diabetes and breast cancer, will be dealt with separately. To date, relatively few diseases that fall into both these categ
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1.1 What is genetic testing?

When most people encounter genetic testing today, it is usually in a medical context. We may be referred by our GPs to a regional genetics unit, or we may approach our doctors, asking for genetic tests because we suspect something about our family history. In this unit we look at the issues and problems facing individuals and families when confronted with genetic testing.

The technologies that make genetic testing possible range from chemical tests for gene products in the blood,
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Learning outcomes

After studying this unit you should understand:

  • something of the role of a genetic counsellor and its non-directiveness

  • the difference between pre-natal diagnosis, childhood testing and adult testing and give some examples of diseases that may be tested for

  • the ethical and moral difficulties involved in making decisions on whether or not to carry out such tests


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2.5 Critical current

The current density for a steady current flowing along a wire in its normal state is essentially uniform over its cross-section. A consequence of this is that the magnetic field strength B within a wire of radius a, carrying current I, increases linearly with distance from the centre of the wire, and reaches a maximum value of μ0I / 2Author(s): The Open University

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2.4 Critical magnetic field

An important characteristic of a superconductor is that its normal resistance is restored if a sufficiently large magnetic field is applied. The nature of this transition to the normal state depends on the shape of the superconductor and the orientation of the magnetic field, and it is also different for pure elements and for alloys. In this subsection we describe the behaviour in the simplest situation; we shall discuss other more complex behaviour in Section 4.

If an increasing magnet
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2.2 Persistent currents lead to constant magnetic flux

An important consequence of the persistent currents that flow in materials with zero resistance is that the magnetic flux that passes through a continuous loop of such a material remains constant. To see how this comes about, consider a ring of metal, enclosing a fixed area A, as shown in Figure 6a. An initial magnetic field B0 is applied perpendicular to the plane of the ring when the temperature is above the critical temperature of the material from which the rin
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2.1 Zero electrical resistance

In this section we shall discuss some of the most important electrical properties of superconductors, with discussion of magnetic properties to follow in the next section.

The most obvious characteristic of a superconductor is the complete disappearance of its electrical resistance below a temperature that is known as its critical temperature. Experiments have been carried out to attempt to detect whether there is any small residual resistance in the superconducting state. A sensitive t
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1 Superconductivity

Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes (Figure 1) as he studied the properties of metals at low temperatures. A few years earlier he had become the first person to liquefy helium, which has a boiling point of 4.2 K at atmospheric pressure, and this had opened up a new range of temperature to experimental investigation. On measuring the resistance of a small tube filled with mercury, he was astonished to observe that its resistance fell from ~0.1 Ω at a temper
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