Websites Reaction Biology

The Malaria Parasite Metabolic Pathway (MPMP) is a website (http // sites.huji.ac.il/malaria last accessed 16 July 2008) that contains over 120 maps that encompasses not only classical biochemical pathways but next to each entry there is a 48-h clock that depicts stage-dependent transcription of a particular gene in P. falciparum. At the clock s zero hour, merozoites invade and at 12 o clock the 48-h cycle terminates. In the middle of the clock appears the hour of maximal transcript level. Clicking on the clock links to a transcriptomic database (http //malaria. ucsf.edu last accessed 16 July 2008). The enzymes are also linked to the International Union of Biochemistry and Molecular Biology website (http //www.iubmb.org last accessed 16 July 2008) where there is a detailed chemistry of the enzymatic reaction. Unlike other databases MPMP has been developed, curated and updated manually (Ginsburg, 2006). 

Some of the energy released in the metabolism of foods is not given out as heat, but is used to make a substance called adenosine triphosphate (ATP). ATP maybe converted to adenosine diphosphate (ADP) when required, and it is the ATP ADP reaction that produces the energy upon which we depend for the synthesis of biologically important molecules, for the transport of vital nutrients within the body and for muscle action (see Appendix 13 in the website). 

Catalysts are often specific, i.e. they will only afiect the rate of a particular reaction. This is particularly true of some biological catalysts (enzymes). Enzymes are proteins. They are often deactivated (or even destroyed) if the temperature rises much above 40 °C (Fig. 14.9). Most enzymes operate in a narrowband of pH, and many require the presence of a metal ion or another complex organic molecule as cofactor. For more about enzymes, see Case Study 1 on the website. 

Biological catalysts are known as enzymes (Chapter 23 on the accompanying website) and consist of proteins, often associated with metal ions. A substance that decreases the rate of a reaction is called an inhibitor. An example of an inhibitor is the anti-knock compound, tetraethyl lead(iv), which was used to prevent pre-ignition in leaded petrol vapour but has now been banned in practically all countries (Chapter 10). There are many specific and general inhibitors known for enzymes many nerve gases and poisons, for example cyanides, operate as enzyme inhibitors, often by interacting with the active site of the enzyme (Figure 6.13). 

Electron transfer reactions are central to many of the metabolic processes necessary for the survival of all living organisms. These reactions depend upon the approach of an electron donor and an electron acceptor. In biology, intermolecular electron transfer is common and occurs between sites on different proteins. This leads to electron-transfer chains that function as a series of consecutive electron-transfer reactions between metal sites within a protein or group of proteins (Chapter 9). Electron-transfer chains are important in photosynthesis and respiration (see Chapter 23 on the accompanying website). 

Biochemists know these two forms of butenedioic acid by different (non-systematic) names. Fumaric acid (trans-butenedioic acid) is an intermediate in the Krebs cycle, an essential part of aerobic respiration for energy release in cells (Chapter 15, and Chapter 23 on the accompanying website). Maleic acid (cis-butenedioic acid) is an inhibitor of reactions involved in the interconversion of amino acids in the liver. These different biological roles are a consequence of the molecules different shapes and their interactions with the enzymes involved in metabolic pathways. 

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