Biomolecules II

Many biomolecules are made up of smaller units in a modular fashion, and they can be broken down into these units again. The construction of these molecules usually takes place through condensation reactions involving the removal of water. Conversely, their breakdown functions in a hydrolytic fashion—i.e., as a result of water uptake. The page opposite illustrates this modular principle using the example of an important coenzyme. 

Coenzyme A (see also p. 106) is a nucleotide with a complex structure (see p. 80). It serves to activate residues of carboxylic acids (acyl residues). Bonding of the carboxy group of the carboxylic acid with the thiol group of the coenzyme creates a thioester bond (-S-CO-R see p. 10) in which the acyl residue has a high chemical potential. It can therefore be transferred to other molecules in exergonic reactions. This fact plays an important role in lipid metabolism in particular (see pp. 162ff), as well as in two reactions of the tricarboxylic acid cycle (see p. 136). 

As discussed on p. 16, the group transfer potential can be expressed quantitatively as the change in free enthalpy (AG) during hydrolysis of the compound concerned. This is an arbitrary determination, but it provides important indications of the chemical energy stored in such a group. In the case of acetyl-CoA, the reaction to be considered is  

In standard conditions and at pH 7, the change in the chemical potential G (AG°, see p.l8) in this reaction amounts to -32 kj mol and it is therefore as high as the AG° of ATP hydrolysis (see p. 18). In addition to the energy-rich thioester bond, acetyl-CoA also has seven other hydrolyzable bonds with different degrees of stability. These bonds, and the fragments that arise when they are hydrolyzed, will be discussed here in sequence. 

The section of the molecule discussed so far represents a functional unit. In the cell, it is produced from pantothenate. The molecule also occurs in a protein-bound form as 4 -phosphopantetheine in the enzyme fatty acid synthase (see p. 168). In coenzyme A, however, it is bound to 3, 5 -adenosine diphosphate. 

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Review Unit 11 Biomolecules II -Lipids, Nucleic Acids, Metabolic Pathways... 

Lord, R. C. and Yu, N. Y. 1970b). Laser-excited Raman Spectroscopy of biomolecules. II.Nativeribonuclease anda-chymotrypsin. J. Mol Biol, 5,203-13. [224]... 

Evans DA, Wales DJ, Dian BC, Zwier TS (2004) The dynamics of conformational isomerization in flexible biomolecules. II. Simulating isomerizations in a supersonic free jet with master equation dynamics. J Chem Phys 120 148... 

Interaction of biomolecules with ginghaosu (artemisinin) and its derivatives in the presence of Fe(II) ion—an exploration of antimalarial mechanism 99PAC1139. 

Depicted in Fig. 2, microemulsion-based liquid liquid extraction (LLE) of biomolecules consists of the contacting of a biomolecule-containing aqueous solution with a surfactant-containing lipophilic phase. Upon contact, some of the water and biomolecules will transfer to the organic phase, depending on the phase equilibrium position, resulting in a biphasic Winsor II system (w/o-ME phase in equilibrium with an excess aqueous phase). Besides serving as a means to solubilize biomolecules in w/o-MEs, LLE has been frequently used to isolate and separate amino acids, peptides and proteins [4, and references therein]. In addition, LLE has recently been employed to isolate vitamins, antibiotics, and nucleotides [6,19,40,77-79]. Industrially relevant applications of LLE are listed in Table 2 [14,15,20,80-90]. 

Fatty alcohol- (or alkyl-)ethoxylates, CoE, are considered to be better candidates for LLE based on their ability to induce rapid phase separation for Winsor II and III systems. (Winsor III systems consist of excess aqueous and organic phases, and a middle phase containing bicontinuous microemulsions.) However, C,E,-type surfactants alone cannot extract biomolecules, presumably because they have no net negative charge, in contrast to sorbitan esters [24,26,30,31]. But, when combined with an additional anionic surfactant such as AOT or sodium benzene dodecyl sulfonate (SDBS), or affinity surfactant, extraction readily occurs [30,31]. The second surfactant must be present beyond a minimum threshold value so that its interfacial concentration is sufficiently large to be seen by... 

The covalent functionalisation of CNTs is the alternative and extremely promising approach for applications in fields such as that of functional and composite materials and that of biology. According to the location of the functional groups, two main strategies are used to covalently functionalise CNTs with biomolecules (i) defect functionalisation, and (ii) sidewall functionalisation. 

GROUP I AND II METALS IN BIOLOGICAL SYSTEMS HOMEOSTASIS AND GROUP I BIOMOLECULES... 

Chapter 6 discussed Group II metal ions in biomolecules, concentrating on magnesium ions in catalytic RNA and on two calcium-containing biomolecules calmodulin and Ca -ATPase. Readers interested in the evolutionary aspects of catalytic RNA as a precursor to the DNA-based life forms that exist in the present time could begin by consulting the publications fisted in... 

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