Why Learn Chinese?
Why Learn Chinese?
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4.2 Reducing eutrophication

In Britain, water supply companies have tended to regard eutrophication as a serious problem only when it becomes impossible to treat drinking water supplies in an economic way. Threshold concentrations at which action is taken to reduce nutrient loadings thus depend on economic factors, as well as wildlife conservation objectives.

There are two possible approaches to reducing eutrophication:

  1. Reduce the source of nutrients (e.g. by phosphate str
    Author(s): The Open University

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4.1 Measuring and monitoring eutrophication

During the 1990s there was increased demand in the UK for effective methods of monitoring eutrophication. There was also considerable interest in the development of monitoring systems based on biotic indices. Several ‘quality indices’ based on a variety of organisms were explored. For monitoring tools to have practical application, they must satisfy certain requirements:

  • sampling must be quick and easy;

  • monitoring must be based on
    Author(s): The Open University

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3.2 Anthropogenic sources of nutrients

In addition to the natural sources of nutrients referred to above, nitrogen and phosphorus enter the environment from a number of anthropogenic sources. These are considered below.


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The DPS protein compacts the eubacterial chromosome during stress

When an E. coli cell enters into stationary phase, transcription and cell division cease completely. In such cells, the normal chromatin components, such as those described above, are replaced by a negatively charged protein called DPS. The interaction between DPS and DNA appears to be a specialised bacterial adaptation to survive starvation. In normal conditions of growth, the DNA within the bacterial cell is distributed evenly throughout the entire cytoplasm. In stationary cells, how
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6.2 Non-covalent bonding in site-specific binding

The affinity of a protein for DNA is determined in thermodynamic terms by the free energies of the individual components compared to the free energy of the DNA-protein complex. DNA binding proteins, which contain different binding motifs, demonstrate a wide range of thermodynamic strategies.

The affinity of a site-specific DNA binding protein for its specific DNA sequence is generally of the order of 104−107 times greater than its affinity for non-specific sequen
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4.6 Summary

  1. RNA chains play fundamentally important roles within the cell, including genetic information transfer (mRNA), components of the translation machinery (rRNA in ribosomes and tRNAs) and as regulatory small RNAs.

  2. The tertiary structure of RNA is determined by interactions that maximise base pairing. Despite instability and isolation problems, the tertiary structures of several major cellular RNAs are known.

  3. Transfer RNA struct
    Author(s): The Open University

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Aptamers

Aptamers are nucleic acid molecules that have been developed to mimic the selective and tight binding of other molecules such as antibodies. In order to identify an aptamer that is capable of binding to a target molecule, a process called Selex (systematic evolution of ligands by exponential enrichment) is utilised. The strategy relies upon a combination of a selective binding assay and amplification by PCR. A ‘library’ of short single-stranded DNA oligonucleotides is synthesised <
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Antisense regulation of gene expression

The term antisense refers to the use of a nucleic acid that is complementary to the coding (i.e. ‘sense’) base sequence of a target gene. When nucleic acids that are antisense in nature are introduced into cells, they can hybridise to the complementary ‘sense’ mRNA through normal Watson-Crick base pairing. Synthetic antisense DNA chains as short as 15–17 nucleotides in length have been used to block specific gene expression by either physically blocking translation of the tar
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3.2 Higher-order DNA structures: DNA twisting and torsional effects

As discussed earlier, the helical nature of DNA results for the most part from the properties of the bases, their interactions and the geometry of the helix itself. There is, however, another important contributor to the structure of DNA that is found within the cell. The DNA helix is actually under a torsional stress due to what is called DNA twisting, which arises when the two strands of the helix are twisted around the axis, as shown in Figure 11a.


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1.2 Nucleic acids: genetic, functional and structural roles in the cell

The first role that one immediately thinks about for nucleic acids is that of an inherited genetic material, principally in the form of DNA. In some cases, the inherited genetic material is RNA instead of DNA. For example, almost 60% of all characterised viruses have RNA genomes and these are more common in plant viruses than in animal viruses. There is considerable variation in the amount of genetic material present within organisms (Author(s): The Open University

Learning outcomes

After studying this unit you should be able to:

  • define and use each of the terms printed in bold in the text;

  • understand the properties of nucleotides, how they contribute to secondary and tertiary structures of nucleic acids at the molecular level, and how torsional states are maintained in cellular DNA;

  • understand the different composition and roles of nucleic acids in the cell and their interactions with each other and with agents that cau
    Author(s): The Open University

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Acknowledgements

Except for third party materials and otherwise stated (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:

Author(s): The Open University

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1.3 Summary of Section 1

  1. Water is a renewable resource; globally there is a virtually constant supply of fresh water, as water is recycled by natural processes, but it is unevenly distributed.

  2. A few litres of water per day are needed per person for human survival. For subsistence, the daily requirement is 20–40 litres per person; this includes the use of water for cooking and washing in addition to drinking, but not water for growing food. Water use in industrialise
    Author(s): The Open University

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Learning outcomes

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

4.5 Generating carbon — the legacy of volcanoes

What is the origin of the carbon within the carbon cycle? Figure 1.9 showed that the great
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3.3 The Earth's internal heat

The occurrence of both volcanoes and hot springs shows that the Earth's interior is hot, producing molten rock at temperatures up to 1250 °C, and also superheated steam. However, these phenomena are mainly confined to several narrow zones along the world's active plate boundaries. Many measurements have now been made of the amount of heat flowing from the Earth's interior. Outside the distinctive zones mentioned above, heat flow varies from 40–120 milliwatts per square metre (mW m−2
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2.3 Broadband spectra

The broadband spectrum is the spectrum over all the observed wavelength ranges. To plot the broadband spectrum of any object it is necessary to choose logarithmic axes.

  • Why is it necessary to use logarithmic axes?

  • Because both the spectral flux density, Fλ, and the wavelength vary by many powers of 10.

Author(s): The Open University