Introduction Even the simplest organisms can detect and respond to events in their ever-changing environment. Similarly, within a multicellular organism, cells are surrounded by an extracellular environment from which signals are received and responded to. Extracellular events are decoded and transmitted to relevant parts of individual cells by way of a series of activation/deactivation steps involving many intracellular molecules. This relay of information along molecular pathways is called signal tra
7.1 Introduction You will already be aware of some of the many experimental techniques employed to study protein structure, including X-ray diffraction, CD, NMR and SDS–PAGE. There are also many techniques that have been developed to study protein function, of which several are described in this section.
5.3.2 Cooperative binding A feature of some proteins comprising more than one subunit is that binding of a ligand to its binding site on one subunit, can increase the affinity of a neighbouring subunit for the same ligand, and hence enhance binding. The ligand-binding event on the first subunit is communicated, via conformational change, to the neighbouring subunit. This type of allosteric regulation is called cooperative binding. Haemoglobin, as we have already discussed, is a tetramer consisting of two
5.2 All proteins bind other molecules All proteins bind to other molecules (generically termed ligands). Ligands that can bind to proteins include: ions, e.g. Ca2+; small molecules, e.g. H2O, O2 and CO2, glucose, ATP, GTP, NAD; macromolecules, i.e. proteins, lipids, polysaccharides, nucleic acids. These interactions are specific and key to the protein's function and, of course, are critically d
4.1 Introduction The availability of genomic sequence data from every major taxonomic group of organisms on Earth has allowed extensive comparisons to be made between their protein-coding regions, with over 800 000 protein sequences from these organisms being available for comparison in 2003. From these comparisons, it has become apparent that there is extensive homology between the amino acid sequences of many proteins, even between apparently distantly related organisms. In some proteins, this homology exte
3.1 Introduction That proteins contain functionally and physically discrete modules or domains is an important principle, one that will be reinforced as we examine the roles of specific proteins in a variety of different cellular processes. There are several advantages conferred by multidomain protein architecture: Creation of catalytic or substrate-binding sites These sites are often formed at the interface between two domains, typically a cleft. Movement
1.6 Fibrous proteins Most of the proteins described so far have been globular proteins. There are, however, some distinctive features that characterise fibrous proteins and we present here a general overview of these. Elongated fibrous proteins frequently play a structural role in the cell. They do not readily crystallise but tend to aggregate along their long axis to form fibres. X-ray diffraction studies of these fibres, in contrast to analysis of protein crystals, provides only very limited information on the
1.4.2 Protein fold Protein folds are often very extensive arrangements, combining elements of secondary and supersecondary structure. Some of the most common protein folds are described in Table 4: view document with examples of proteins that contain them. Notice that proteins can be conveniently divided into three classes, on the basis of the elements of secondar
8.7 Luminosity functions Samples of galaxies can be biased due to the flux limit of the sample that is observed. This is the so called Malmquist bias. Read Pe 7.3 Polarization of electromagnetic radiation So far we have described electromagnetic radiation in terms of its wavelength, frequency and speed. It has another, sometimes important, property: polarization. Figure 10 shows the electric and magnetic field in a plane-polarized electromagnetic wave. In any electromagnetic radiation, the electric an 1.3.3 A breeding experiment: stage two We now turn to the second stage of the breeding experiment, but this time we will follow the phenotypes and genotypes simultaneously. The purple (Gg) grains of the F1 generation are planted and when these have developed into mature F1 plants they produce male and female flowers. These F1 plants are crossed with each other, as shown in Figure 8. The fertilised ovules develop into grains borne on cobs, and these grains are the beginning of the second f References 5.2 Type 1 diabetes Type 1 diabetes was previously called insulin-dependent diabetes. This is because in people with Type 1 diabetes their pancreas fails to produce insulin and they are dependent on taking insulin for their treatment. It would be useful to look back at Figure 5 to remind yourself of the actions of insulin. As we have already discuss 3.8 Glucagon Glucagon is another hormone produced by the pancreas. Question: Can you recall which cells make glucagon? 14 Unit questions and answers Note: Question 1 is included in Section 3. 8 Managing the BSE/vCJD episode up to May 1990 BSE was formally recognised as a new disease in November 1986. However, this information was kept under ‘embargo’ at first while an initial epidemiological study – involving the collection of data from 200 herds – was started. The Ministry of Agriculture, Fisheries and Food (MAFF) was officially informed about BSE by the Chief Veterinary Officer (CVO) in June 1987. By December 1987, those responsible for analysing the data from the initial epidemiological study had concluded that the 5.3 Heat production There are two graphs in this section, Figure 2 and Author(s): Introduction Mammals come in a bewildering variety of shapes and sizes and yet all of the 4700 or so species have some characteristics in common. Indeed, it's the existence of these common features that justifies the inclusion of all such diverse types within the single taxonomic group (or class) called the Mammalia. This is the first in a series of units about studying mammals. To get the most from these units, you will need access to a copy of The Life of Mammals (2002) by David Attenboroug 1.4.6 The signed area under a constant velocity–time graph There is a simple feature of uniform velocity–time graphs that will be particularly useful to know about when we come to consider non-uniform motion in the next section. It concerns the relationship between the velocity–time graph and the change in position over a given time interval. Consider the following problem. A vehicle travels at a velocity vx = 12 m s−1 for 4 s. By how much does its position change over that interval? The answer, fro 1.3.5 A note on graph drawing There will be many occasions throughout your study of physics when you will need to draw graphs. This subsection gives some important guidelines for this activity.
Decide which is the independent variable and which the dependent variable. Plot the independent variable along the horizontal axis and the dependent variable along the vertical axis. This is purely a convention but is why, for instance, we usually plot the time
Activity 9: Radio-quiet quasars
Question 2
