Structures of simple sugars, starch and cellulose, peptides ..., Lecture notes of Accounting

Download Structures of simple sugars, starch and cellulose, peptides ... and more Lecture notes Accounting in PDF only on Docsity! CHM 224 -Structures of simple sugars, starch and cellulose, peptides and proteins. (online module v) BY: OKE, DG SIMPLE SUGARS - Introductions Carbohydrates are polyhydroxy aldehydes, ketones or compounds that can be hydrolysed from them. A carbohydrate that cannot be hydrolysed to simpler compound is called a monosaccharide. A carbohydrate that can be hydrolysed to two monosaccharide molecules is called a disaccharide while a carbohydrate that can be hydrolysed into many monosaccharide molecules is called a polysaccharide. Simple sugars - structures OH O H OH H OH OH H H OH OH OH H H OH H OH O OH 2,3,4,5,6-pentahydroxyhexanal 1,3,4,5,6-pentahydroxyhexan-2-one D- Glucose D- Fructose OH O OH H H OH 2,3,4-trihydroxybutanal D-Threose Disaccharides Disaccharides are carbohydrates that are made up of two monosaccharide units. Examples are : (+)-maltose (malt sugar), (+)- cellobiose (cotton fibre), (+)-lactose (milk sugar) and (+)-sucrose (cane of beet sugar). (+)-Maltose has the molecular formula C12H22O11 and is made up of two units of D-(+)-glucose units joined by an alpha glycosidic bond. It is obtained from partial hydrolysis of starch. O OHOH H H H H HOH O OH O OH H H H H OH OH OH Structure of maltose Sucrose (+)-sucrose is the common table sugar, obtained from sugar cane and beets. It is a non-reducing sugar. It is made up of a D-glucose and D-fructose units. ◦ Structure of Sucrose O OH H H H H OH OH OH H O O OH H OH H OH H OH Polysaccharides The polysaccharides cellulose, starch, and glycogen are all polymers of D-glucose units linked by glycosidic bonds. Cellulose is the major structural component of the cell walls of plants and is the most abundant organic compound on Earth, accounting for more than half of the carbon in the biosphere. It is a linear polymer containing 2500 to 15,000 D-glucose units linked by β-glycosidic bonds between carbons 1 and 4. O HOH H H H H OOH -O OH O HOH H H H H OOH OH O HOH H H H H O~OH OH CELLULOSE Amylopectin contains up to 106 glucose units. It differs from amylose in that it has branches that occur every 20 to 30 glucose units. These branches are also amylose-type chains that are connected to the main chain by an α -glycosidic bond from carbon 1 of the branch to carbon 6 of the main chain. Branches occur on the branches also, so amylopectin has a treelike structure. Glycogen, the food reserve of animals, has a structure similar to that of amylopectin except that it has branches every 8 to 10 glucose units. O OOH H H H OH O O OH H H H H OH OH O OH H H H H OH OHH H H H O O OH H H H OH OH O -O H O OH H H H OH OH HH H O~ -O Amylopectin Peptides and Proteins Amino acids and the polymers that are formed from them, peptides and proteins, are among the most important compounds found in living organisms. They act as structural components, catalysts, hormones, neurotransmitters, and essential nutrients, among other things. Peptides and Proteins Because they contain two functional groups, amino acids can react to produce condensation polymers by forming amide bonds. These polymers are called peptides, polypeptides, or proteins. Although there is no universally accepted distinction, the term protein is usually reserved for naturally occurring polymers that contain a relatively large number of amino acid units and have molecular masses in the range of a few thousand or larger. The term peptide is used for smaller polymers. As a simple example, the dipeptide formed by the reaction of two glycines has the following structure: +NH2 OH O NH2 OH O NH2 NH OH O + OH2 Amide/peptide bond By convention, peptides are written so that the end with the free amino group, called the N-terminus, is on the left and the end with the free carboxyl group, the C-terminus, is on the right. Because it takes considerable space to show the structure of even a small polypeptide like this one, it is common to represent the structures of peptides and proteins by using the three-letter abbreviation for each amino acid. Thus tuftsin, with a threonine N- terminal amino acid, followed by lysine, proline, and, finally, arginine as the C-terminal amino acid, is represented as Thr-Lys-Pro-Arg.