Software Development: Testing
Software Development: Testing
Web 3.0
Web 3.0
Lesson 03 - One Minute Luxembourgish
In lesson 03 of One Minute Luxembourgish you will learn to say that you can speak a little Luxembourgish. Remember - even a few phrases of a language can help you make friends and enjoy travel more. Find out more about One Minute Languages at our website - http://www.oneminutelanguages.com. One Minute Luxembourgish is brought to you by the Radio Lingua Network and is ©Copyright 2008.Author(s):
Technology Water Supply, Desalination and Energy Recorded 12/15/11
How able a King was Richard III? Rising food prices in Kenya A short video depicting the problems faced by Kenyans as a result of sharply rising food prices (such as the price of maize, beans and cooking oil). Extreme Photoshop Makeover A photographer and designer shows the photo retouching process in detail. Arctic Sea Ice 2008 The polar ice caps have been shrinking in summer and expanding in winter for millions of years. But in the last 3 decades, the arctic sea ice at the end of each summer's melt has been getting steadily smaller. Turkish President on miners' deaths: 'Our pain is so big' 4.4 Reducing nutrient availability Once nutrients are in an ecosystem, it is usually much harder and more expensive to remove them than tackle the eutrophication at source. The main methods available are: precipitation (e.g. treatment with a solution of aluminium or ferrous salt to precipitate phosphates); removal of nutrient-enriched sediments, for example by mud pumping; and removal of biomass (e.g. harvesting of common reed) and using it for thatchi 2.4.1 Estuarine species Nutrient runoff from the land is a major source of nutrients in estuarine habitats. Shallow-water estuaries are some of the most nutrient-rich ecosystems on Earth, due to coastal development and the effects of urbanization on nutrient runoff. Figure 2.19 shows some typical nitrogen pathways. Nitrogen loadings in rainfall are typically assimilated by plants or denitrified, but septic tanks tend to add nitrogen below the reach of plant roots, and if situated near the coast or rivers can lead to 8.3 Chromosome distribution within the nucleus DNA from any one particular chromosome is a single chain, many millions of bases long, and this chain is attached to a scaffold structure. It is not surprising then, that if we examine the interphase nucleus, each chromosome is seen to fill a localised area. This localised distribution of individual chromosomes is illustrated in Figure 42 with an examination of human chromosomes within the interphase nucleus. In these examples, special DNA probes have been used to detect the location of the e 8.2 Chromosome scaffolds Most of the chromosomal DNA chains within the interphase nucleus are believed to be held on a scaffold or backbone structure made from various proteins, with loops of between 20 and 200 kb extruding from attachment sites. This chromosome structure is shown schematically in Figure 40. The scaffold, as well as permitting further compaction, serves to bring the DNA together in organised regions. There are many different protein components of these scaffolds, amongst them DNA topoisomerases. 8.1 Introduction The average human cell has around two metres of DNA within its nucleus. In the interphase nucleus, in which transcription and replication are going on, this DNA is packaged into nucleosomes that are variably compacted, through association with H1, into larger 30nm fibres. In fact, the average nucleus most likely contains DNA with a continuum of chromatin configurations, ranging from highly open 10 nm fibres, through to 30 nm fibres and fibres that are even more tightly packed together, call Core histone tail modification regulates DNA compaction What effect would neutralising the positive charges on the octamer N-terminal tails have upon the compaction of DNA by H1? The histone fold and formation of the nucleosome We have seen how in the eubacterial chromosome, bending DNA serves to facilitate its compaction. A similar process occurs in eukaryotic cells in that DNA is bent and wrapped around a protein unit. In this case, the core unit is a protein–DNA complex termed a nucleosome. The nucleosome comprises the core histone proteins H2A, H2B, H3 and H4 arranged in a structure known as the core histone octamer, with an associated length of DNA. In order to understand how the nucleosome is a The histone proteins The genes for the histone proteins are very highly conserved across eukaryotes, reflecting their importance in DNA packaging. The histone family consists of five groups of proteins, histones H1, H2A, H2B, H3 and H4. An examination of their amino acid content gives us clues as to how the histones fulfil their role in DNA packaging. Rather like the polyamines in bacteria, these proteins are highly positively charged, with up to 20% of their amino acids being lysine or arginine, the charged side 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 7.2 The eubacterial chromosome Some of the diverse roles of chromatin components can be illustrated by examining the E. coli chromosome. Like most prokaryotes, E. coli has a single chromosome consisting of a single double-stranded circular DNA molecule. There is no nucleus present, but the E. coli DNA is within a discrete entity in the cytoplasm called the nucleoid. The nucleoid contains a multitude of proteins and is in close proximity to the ribosomes, where translation occurs. In addition to 7.1 Introduction Until now, we have discussed DNA primarily as a double helix, but in its natural state within the cell it is found packaged as a complex mixture with many different proteins and other components. You have already seen examples of proteins with specific roles to play, such as topoisomerases and the proteins with various DNA binding domains, but in this section we will turn our attention to the proteins that serve to pack and organise the DNA into what we call chromatin. The packaging of
How able a King was Richard III? A presentation by Dr. David Grummitt, Senior Research Fellow, The History of Parliament Project, for The History Faculty: www.thehistoryfaculty.com.
History as written and presented by current historians. Visit thehistoryfaculty.com for free downloads and more information.
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May 15 - Turkish President Abdullah Gul says the whole nation is in pain after nearly 300 miners were killed in an explosion as anger grows over workplace safety standards. Jennifer Davis reports.
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SAQ 34
