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According to the IUPAC definition of a hemiacetal, the R 1 and R 2 groups may or may not be hydrogen. In a hemiketal, both of these R-groups must not be hydrogen. Thus, hemiketals are regarded as a subclass of hemiacetals. [1] The prefix hemi, meaning half, refers to the one alcohol added to the carbonyl group.
Generic structure of acetals. In organic chemistry, an acetal is a functional group with the connectivity R 2 C(OR') 2. Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments not hydrogen. The two R' groups can be equivalent to each ...
Structural chemistry is a part of chemistry and deals with spatial structures of molecules (in the gaseous, liquid or solid state) and solids (with extended structures that cannot be subdivided into molecules). For structure elucidation [1] a range of different methods is used.
The nitrogen atoms from the amino group in the nucleotides are covalently linked to the anomeric carbon of the ribose sugar structure through an N-glycosidic bond. Occasionally, the nucleobases attached to the ribose undergo deamination, alkylation, or oxidation which results in cytotoxic lesions along the DNA backbone.
[9] [10] Several forms of glucan synthase from CSLF and CSLH have been identified. [9] [10] All of them are responsible for addition of glucose to the backbone and all are capable of producing both β1-3 and β1-4 linkages, however, it is unknown how much each specific enzyme contributes to the distribution of β1-3 and β1-4 linkages. [9] [10]
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For example, acetylation of histones by histone acetyltransferases (HATs) results in an expansion of local chromatin structure, allowing transcription to occur by enabling RNA polymerase to access DNA. However, removal of the acetyl group by histone deacetylases (HDACs) condenses the local chromatin structure, thereby preventing transcription. [9]
The mechanism is tentatively hypothesized to take place by the following steps: [7] The reduced di-iron coordinates oxygen, which oxidizes the iron and forms a peroxide species. The peroxide species attacks the aldehyde. An electron transfer coupled with cleavage of the peroxo species generates a hemi-acetal radical.