George H.W. Bush - Mini Biography
A World War II veteran, George H.W. Bush served as Vice President for two terms before being elected President of the United States in 1988.
2.1 Effects on primary producers in freshwater ecosystems Plant species differ in their ability to compete as nutrient availability increases. Some floating and submerged macrophyte species are restricted to nutrient-poor waters, while others are typical of nutrient-rich sites (see Table 2.2). Figure 2.2 shows turbid water in a polluted drainage ditch associated with localized growth of algae. There are no aquatic plants present. 1.2 Resource availability and species diversity A wide range of ecosystems has been studied in terms of their species diversity and the availability of resources. Each produces an individual relationship between these two variables, but a common pattern emerges from most of them, especially when plant diversity is being considered. This pattern has been named the humped-back relationship and suggests diversity is greatest at intermediate levels of productivity in many systems (Figure 1.5). 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. Nucleosomal DNA packaging into a 30 nm fibre: the role of histone H1 When chromatin is isolated from the nucleus and examined under the electron microscope, it can be seen as a 30 nm fibre. This fibre is formed through the action of the histone H1 on the nucleosomal DNA in the 10 nm fibre. In contrast to the other histone proteins, H1 does not contain the histone fold motif. Compaction of the 10 nm fibre to give the 30 nm fibre is achieved by interaction of the H1 protein with both the linker DNA and the histone octamers, as shown in Figure 31 DNA supercoiling and protein binding in the E. coli chromosome As discussed earlier, the DNA of the E. coli chromosome is highly negatively supercoiled due to the action of the DNA gyrase enzyme (Section 3.2). This negative supercoiling serves to assist in compaction of the DNA, with the repulsive forces of the sugar-phosphate backbones being counteracted by polyamines. Many of the proteins 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 6.3 The recognition of specific DNA sequences by proteins Transcription factors act by binding to specific DNA regions, dependent upon the recognition of particular sequences of bases, usually through direct interactions in the major groove. They are known to use certain motifs for DNA binding and many contain the helix–turn–helix (HTH) or zinc finger motifs. We will now discuss the molecular properties of these two protein motifs that confer DNA binding ability on the proteins that contain them. The classical HTH motif consists of two 4.1 Natural stores of carbon The major natural stores of carbon (called ‘reservoirs’) are shown below in Figure 1.9. 4 Fossil fuels Part of the incoming solar energy becomes stored in fossil fuels (oil, gas and coal: 2.3 Global power demand In Section 2.2 we calculated a value of 14.3 TW for the average global requirement for primary power in 2002 1 Energy use Until about 8000 years ago humans relied on hunting and gathering for food, and burning wood to keep warm. Their exact energy demands can at best only be estimated but to survive they probably needed about as much Author(s): Learning outcomes By the end of this unit you should be able to: 7.6 Questions Suppose that a galaxy has emission lines in its optical spectrum. A line of wavelength 654.3 nm is broadened by 2.0 nm. Estimate the velocity dispersion of the gas giving rise to the broadened spectral line. Is it likely to 7.1 The spectra of galaxies The spectrum of a galaxy is the composite spectrum of the objects of which it is composed. The optical spectrum of a normal galaxy contains contributions from stars and HII regions. An elliptical galaxy has no HII regions and has an optical spectrum that looks somewhat like a stellar spectrum but with rather fainter absorption lines. A spiral galaxy has both stars and star-forming regions, and its optical spectrum is the composite of its st 6.2 Do supermassive black holes really exist? One outstanding feature of the black-hole model is that the black hole must be supermassive. Can one at least detect the presence of a massive central object? How might a massive central object be detected using information from galactic rotation curves? By measuring rotation speeds near the nucleus of the galaxy. The faster the rotation speeds, the greater the enclosed mass. So the answer is yes. In NGC 4151 Radio-loud AGNs The second model (Figure 36b) is similar to the first, but now the engine is producing a pair of jets that will eventually end in a pair of lobes, as seen in radio galaxies and some quasars. Looking at the model from the side, one expects to see narrow lines in the spectrum (but not broad lines) and two 2 What should dialogue with the public aim to achieve? The publication Public Dialogue on Science and Technology, published in 2002 by the Parliamentary Office of Science and Technology (POST), states: Proponents put forward two basic arguments in favour of dialogue. The first is that traditional consultation tends to be unattractive to many people and draws only on ‘predictable’ sources. They argue that dialogue can provide new opportunities for people who 4.4 The ongoing story At the time of writing (2006), the Golden Rice tale is an unfinished story. Some of the developments of the last five years are summarised here. One area of ongoing scientific dispute is the question of whether the enriched rice can contribute significantly to the alleviation of vitamin A deficiency. We have seen that Shiva estimated that at best 100 g of rice a day would provide 4.4% of the recommended daily allowance. More sophisticated theoretical models, published since that time, h
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Question 15
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