C+4 carbon Sn+4 tin (IV), stannic +4 +4 Si silicon Pb lead (IV), plumbic Ge+4 germanium Ti+4 titanium (IV) Mn+4 manganese (IV) -1 all the halogens exhibit the -1 state; several exhibit + states in covalent compounds F-1 fluoride I-1 iodide -1 Cl chloride H-1 hydride Br-1 bromide -2 all the chalcogens exhibit the -2 state for ionic compounds; several exhibit + states in covalent compounds O-2 oxide Se-2 selenide -2 -2 S sulfide Te telluride
solvent, each other and the peptide bond. This is important in what is called helix-capping, in which the unfulfilled H-bonds of the backbone are satisfied. When H-bonded and buried they are effectively no longer polar. The pK of the imidazole of His (6.7) means that at physiological pH it can function either as an acid or a base. Many enzymes use His as a general acid/base catalyst. Cys can make disulfide bonds, which act as covalent cross-links. Charged side chains are usually found on the surface. Buried ones tend to have several H- bonds to "diffuse" the charge. Salt bridges are ion pairs between an acid and basic amino acid. The Asp side chain is more rigid than that of Glu due to the shorter chain in Asp, thus Asp is more frequently found in the active sites of enzymes. Kvaternaarstruktuur on eriti oluline mitmest subühikust koosneva valgu funktsioneerimiseks (ensüümide korral allosteeriline regulatsioon)
[8] 12. (i) max 1 for meaning of term attached to an insoluble material / AW; max 2 for description (micro)encapsulation / (trapped) in alginate beads; adsorption / stuck onto, collagen / clays / resin / (porous) glass; cross linkage / covalent / chemical, bonding to, cellulose / collagen fibres; gel entrapment / trapped inside gel e.g. silica (lattice / matrix); partially permeable membrane (polymer) microspheres; 3 (ii) any three from the following: urine can be processed / no problem of removing urine / AW; pure / drinkable / useable, water produced; A water recycled space saving / less water needs to be taken into space;
Another way to reduce the required be submitted to food regulation (e.g., addi- amount of salt and phosphate is to use micro- tives defined in the Council Directive 89/107/ bial transglutaminase (MTG). It is a calcium- EEC 1989). Most food additives are consid- independent enzyme that catalyzes the ered safe. However, some are known to be polymerization and crosslinking of proteins carcinogenic or toxic. Allergic reactions to through the formation of covalent bonds colorings and hyperactivity from phosphates between protein molecules (Carballo et al. have been reported for sensitive individuals. 2006; Heinz 2007). Although the addition Moreover, some nonmeat ingredients, such of MTG had beneficial effects on reducing as vegetables, egg, or milk proteins, contain cook loss and increasing hardness and chewi- substances that cause allergic reactions in ness, Pietrasik and Li-Chan (2002) found some consumers (e
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