1.1.1 The chemical structure of DNA

This unit explores the chemical nature of the genome. Genomes are composed of DNA, and a knowledge of the structure of DNA is essential to understand how it can function as hereditary material. DNA is remarkable, breathtakingly simple in its structure yet capable of directing all the living processes in a cell, the production of new cells and the development of a fertilized egg to an individual adult.

DNA illustrates beautifully the precise relationship between molecular structure and b
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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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Introduction

Genomes are composed of DNA, and a knowledge of the structure of DNA is essential to understand how it can function as hereditary material. DNA is remarkable, breathtakingly simple in its structure yet capable of directing all the living processes in a cell, the production of new cells and the development of a fertilized egg to an individual adult.

DNA has three key properties: it is relatively stable; its structure suggests an obvious way in which the molecule can be duplicated, or re
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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:

Unit Image

Chase Crowson flickr.com (18 October 2007)

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


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3 The flow of information from DNA to RNA to protein

The information flow from DNA to protein is more complex than shown in Figure 1. The genetic information encoded within the DNA of a gene is carried via an intermediary molecule, RNA (ribonucleic acid). Information within a cell can therefore be seen as passing from DNA, via RNA, to a protein. This flow of information can b
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1.4 Broadly typical phases of PhD research

A modern PhD can be viewed as having three key phases (very roughly, but not strictly, corresponding to the three years of a full-time degree), each of which contributes a necessary element of mastery:

  1. Orientation – mastering the literature and formulating a research problem and plan.

  2. Intensive research – gathering the evidence to support the thesis, whether empirical or theoretical.

  3. Entering t
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1.3 Different models of PhDs within and across disciplines

There are many different models of how a PhD might be conducted. The models are shaped by the expected place of study (e.g. on the OU campus, in an industry laboratory, at the kitchen table), by the intensity of study and focus (e.g. full time, part time), by the number of influences on the research (e.g. student directed, part of a larger research project, part of an industry research programme), by the level of intended guidance (e.g. taught introduction, supervision-as-collaboration, large
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1.1 Thoughts on a PhD

Entering students often think of a PhD as a ‘magnum opus’, a brilliant research project culminating in a great work. This is rather a demanding model, and few students win Nobel Prizes as a result of their doctoral studies. More realistically, a PhD is research training leading to a research qualification. The PhD is a passport to a research career.

There are other views of a PhD, as well. Getting a PhD can be a ‘rite of passage’, prerequisite to admission into the academic ‘t
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2.2 Why study ecology?

These days, bird watching is a popular leisure activity and in the past so were collecting insects, wild flowers and birds’ eggs (although such activities are not now recommended – indeed, they are often illegal – because of the potential damage they cause to flora and fauna). Some amateurs are or were truly experts in their fields. In fact, much of the original identification of the British flora and fauna was done by amateur naturalists. Many a Victorian vicar or other self-taught nat
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1.11 Summary

Rocks are classified into three types according to how they were formed. Igneous rocks are formed by crystallisation from the molten state; sedimentary rocks are deposited at the Earth's surface from water, air or ice; and metamorphic rocks are rocks of any origin that have been subsequently transformed (metamorphosed) by heat and/or pressure, often several kilometres below the Earth's surface.

Rocks are generally either crystalline, i.e. formed of interlocking mineral crystals, or frag
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1.9.1 Moving around the rock cycle

One way of illustrating the possible ways of moving material around the rock cycle is to draw a diagram that places the processes into their geological contexts. Since the rock cycle involves processes occurring on the Earth's surface and also within its interior, we use a cross-section through the Earth's crust and uppermost mantle to do this, as shown in Author(s): The Open University

1.8.2 Interpretation of a geological exposure

We now want to make use of the observations obtained by sketching the exposure, and it is useful to start by briefly summarising the features seen. First of all, you probably noticed the large boulder in the foreground of Figure 16 (which has been attached below for ease of access). Where did this boul
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1.8 Geological fieldwork

Although much can be learned from samples of rocks in the laboratory or at home, the ‘natural habitat’ of rocks is outdoors. Here the distribution and layout of different rocks is visible wherever rocks are exposed in places such as stream beds, cliffs, rocky shorelines, quarries, or road cuttings. The exposed rocks can be studied in just the same detail as individual laboratory samples, and geological fieldwork allows the size and extent of each rock unit to be seen and the relationships
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4.1 Introduction

The second topic in this unit concerns neural ageing – remember the term ‘neural ageing’ is used to mean ageing
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How the AS–AD Model Incorporates Growth, Unemployment, and Inflation
OpenStax College
By the end of this section, you will be able to: Identify periods of economic growth and recession using the aggregate supply–aggregate demand model Explain how […]

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Animal Life Cycles
In this video, students will observe various photographs of animal life cycles and their life cycle stages. It includes the life cycles of a butterfly, chicken, frog and mosquito. Images set to music. This is a good companion teaching resource for a science lesson/unit. (03:26)
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2.3.6 Torus with 1 hole

We need not restrict ourselves to rectangles: we can also build surfaces by identifying edges of other polygons. For example, if we start with a pentagon and identify two pairs of its edges as shown in Figure 33, what do we get? Identifying the edges labelled a and c in the directions indicated, we obtain
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2.3.5 Projective plane

The final surface that can be obtained by identifying edges of a rectangle is even more complicated. Again it cannot be constructed in three dimensions, so is not a surface in space and is hard to visualise. This time we identify both pairs of opposite edges of the rectangle in opposite directions, as indicated by the arrowheads in Author(s): The Open University

2.3.1 Cylinder

The simplest example of a paper-and-glue construction is to make a rectangle into a cylinder by gluing together two opposite edges. We take a closed rectangle ABB' A' in the plane and identify the opposite edges AB and A'B', as shown in Figure 27. This means that:

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Digital Library Object - Graphics-oriented battlefield tracking systems: U.S. Army and Air Force int
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