All matter is composed of basic substances called elements. An element cannot be broken down into esimpler units by chemical reactions;it contains only one kind of atom.An atom is the smallest characteristic unit of an element.A compound is a substance th...[继续阅读]

    Carbohydrates are usually defined as polyhydroxy aldehydes and ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones.Monosaccharides are classified according to (1) the number of carbon atoms present in the molecule and (2) wheth...[继续阅读]

    The basic nutritional requirements of heterotrophic (异养型的),microorganisms are an energy or carbon source,an available nitrogen source,inorganic elements,and water,for some microorganisms,growth factors (生长因子) and oxygen are also needed.The elemental compo...[继续阅读]

    The IUPAC rules for naming alcohols are as follows.These are rules for what are called substitutive names (The names such as methyl alcohol and ethyl alcohol are also approved by the IUPAC).Select the longest continuous carbon chain to which the hydroxyl ...[继续阅读]

    Flavour compounds include other alcohols,esters,carbonyl compounds,organic acids,sulphur compounds,amines and phenols.Quantitatively,and in terms of their flavour-producing effects,the most important compounds present in beverages and spirits are the high...[继续阅读]

    It would be difficult to overemphasize the importance of proteins in living systems.For instance,certain types of proteins form important parts of structural components in all cells and in spaces between cells. Furthermore,enzymes,antibodies (抗体)[ which a...[继续阅读]

    Some enzymes are produced consititutively,that is,they are always made in substantial amounts when cells are growing.Other enzymes are inducible,that is,they are formed only in the presence of key substrates in the medium.The structural genes of inducible...[继续阅读]

    The basic structure of the penicillins is 6-aminopenicillanic acid(6-APA)made up of a thiazolidine ring fused with a β-lactam ring.The 6-amino position carries a variety of acyl substituents.In the absence of addition of side-chain precursors to the ferme...[继续阅读]

    Biosynthetic metabolic pathways(生物合成代谢途径) often have a common enzyme sequence and then branch leading to more than one end-product.Microorganisms have evolved feedback mechanisms,whereby a build-up of one end-product cause a feedback effect on the first e...[继续阅读]

    A cup of sugar left undisturbed for twenty years will change very little. But when you put some of the sugar in your mouth,it undergoes chemical change very rapidly. Enzymes secreted by some of your cells account for the difference in the rate of change,E...[继续阅读]