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所在平台: Udemy |
课程主页: https://www.udemy.com/course/biomolecules-o/
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**课程名称：** 生物分子 (Biomolecules) **课程概述：** 本课程主要介绍碳水化合物（Carbohydrates）这一类重要的生物分子。课程首先回顾了碳水化合物的早期定义——其化学式常可表示为 Cx(H2O)y，即碳的水合物。然而，这一定义存在局限性，例如，一些具有典型碳水化合物化学性质的化合物（如 rhamnose, C6H12O5）无法用此公式表示，而另一些（如 formaldehyde, CH2O）虽然符合该公式却不具备碳水化合物的性质。 因此，课程给出了更精确的碳水化合物定义：多羟基醛（polyhydroxy aldehydes）或多羟基酮（polyhydroxy ketones），或是水解后能产生这些物质的化合物，并且至少含有一个手性碳原子（chiral carbon atom）。同时指出，碳水化合物中的醛基和酮基通常并不以游离形式存在，而是与分子中的一个羟基结合形成半缩醛（hemiacetals）或半缩酮（hemiketals）。 **课程内容分类：** 根据是否能发生水解以及水解产物的数量，碳水化合物被分为三大类： 1. **单糖 (Monosaccharides)：** * 定义：指不能被水解生成更简单碳水化合物的多羟基醛或多羟基酮。 * 例子：葡萄糖（glucose）和果糖（fructose），分子式均为 C6H12O6。 2. **寡糖 (Oligosaccharides)：** * 定义：指水解后能生成少量单糖分子的碳水化合物。 * 分类举例： * 二糖（Disaccharides），水解后生成两个单糖分子。 * 三糖（Trisaccharides），水解后生成三个单糖分子，例如 raffinose (C18H32O16)。 * 四糖（Tetrasaccharides）等。 3. **多糖 (Polysaccharides)：** * 定义：指高分子量的碳水化合物，水解后能生成大量单糖分子。 * 例子：淀粉（starch）和纤维素（cellulose），分子式均为 (C6H10O5)n。 **教学大纲：** 无。
The group of compounds known as carbohydrates received their general name because of early observations that they often have the formula Cx(H2O)y - that is, they appear to be hydrates of carbon.The above definition could not survive long due to the following reasons:(i) A number of compounds such as rhamnose, (C6H12O5) and 2-deoxyribose (C5H10O4) are known which are carbohydrates by their chemical behaviour but cannot be represented as hydrates of carbon.(ii)There are other substances like formaldehyde (HCHO, CH2O) and acetic acid [CH3COOH, C2 (H2O)2] which do not behave like carbohydrates but can be represented by the general formula, Cx(H2O)y.Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones or substances which give these on hydrolysis and contain at least one chiral carbon atom. It may be noted here that aldehydic and ketonic groups in carbohydrates are not present as such but usually exist in combination with one of the hydroxyl group of the molecule in the form of hemiacetals and hemiketals respectively.ClassificationThe carbohydrates are divided into three major classes depending upon whether or not they undergo hydrolysis, and if they do, on the number of products formed.(i)Monosaccharides: The monosaccharides are polyhydroxy aldehydes orpolyhydroxy ketones which cannot be decomposed by hydrolysis to give simpler carbohydrates. Examples are glucose and fructose, both of which have molecular formula, C6H12O6.(b) Trisaccharides, which yield three monosaccharide molecules on hydrolysis. Example is raffinose, which has molecular formula, C18H32O16.(c)Tetrasaccharides, etc.(iii)Polysaccharides: The polysaccahrides are carbohydrates of high molecular weight which yield many monosaccharide molecules on hydrolysis. Examples are starch and cellulose, both of which have molecular formula, (C6H10O5)n.
