The aldehyde-sugars are called aldoses and the ketone-sugars are called ketoses ( Figure 13.1). Therefore, sugars are polyhydroxy aldehydes or polyhydroxy ketones. Monosaccharides combine two organic chemical functional groups: they have a carbonyl (C=O) group, which is either an aldehyde (with the carbonyl carbon bonded to one carbon atom and one hydrogen atom) or a ketone (with the carbonyl carbon bonded to two other carbon atoms), and they also have at least two carbons bearing hydroxyl (alcohol) groups (-C-OH). What are sugars? Figure 13.1 Aldehyde sugars are called aldoses (left, ribose) and ketone sugars are called ketoses (right, ribulose). All monosaccharides share some chemical properties: they are very water-soluble, poorly soluble or insoluble in organic solvents such as ether or hexane, colorless, and, at least in most cases, sweet to the taste and have the approximate formula (CH 2O) n. many monosaccharide units are called disaccharides, trisaccharides … polysaccharides. Simple sugars, with only one sugar unit, are called monosaccharides. They are also found attached to many proteins (“glycoproteins”). We will be looking at the general principles of carbohydrate chemistry.Ĭarbohydrates are of great importance in energy metabolism, and are essential components of nucleic acids (RNA and DNA). However, only a few of these sugars are commonly found in cells, and for the purposes of this course, we only need to consider a few specific sugars. Unlike the proteins, which are built from a limited set of building blocks (the amino acids), the number of possible sugar molecules is very large. Sugars are the most abundant biomolecule on earth. Carbohydrates, in common speaking, are called “sugars”.
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