Carbohydrates

Carbohydrates are used by organisms as a source of energy, as building materials, and as cell surface makers for cell-to-cell identification and communication 

• Carbohydrates contain carbon, hydrogen, and oxygen atoms in 1 : 2 : 1 ratio

• Carbohydrates can be classified into: 

 
monosaccharides: simples sugars with many _OH groups 

    

disaccharides: 2 monosaccharides covalently linked

    

polysaccharides: a few monosaccharides

    

oligosaccharides: chains of monosaccharides or disaccharide units

The term saccharide and the suffix -ose both refer to sugars.

• Glycosidic Bond ---> a bond between 2 monosaccharides to form disaccharides

• Condensation---> the process of putting together by removal of water

• Hydrolysis---> opposite of condensation, a large molecule is split into smaller sections by breaking a bond, adding a -H to one section and -OH the other. The products are simpler substances.

Monosaccharides                                                     

• Aldoses---> have aldehyde group at one end (RCHO), and ketoses---> have keto group usually at C2 (RC=OR)

• May be distinguished by the carbonyl group they posses_ aldehyde or ketone, and the number of atoms in their carbon backbone.

• Sugar with 5 carbons is called a pentose, one with 6 carbons a hexose

• Simplest monosaccharides are dihydroxyacetone and glyceraldehyde

• Glucose, galactose and fructose are isomers, they posses the same number and types of atoms but a different arrangement of those atoms

Disaccharides                                                           

• It's formed when two sugars are joined together and a molecule of water is removed. 

• Lactose is made from glucose and galactose 

• Cane sugar, sucrose is made from glucose and fructose

• Maltose is also a disaccharide

Polysaccharides                                                       

• Also known as complex carbohydrates are monosaccharide polymers composed of several hundred to several thousand monosaccharide subunits held together by Glycosidic Linkages.

• Some are in form of straight chains while others are branched 

• Serve 2 important functions in living cells: energy storage and structural support

• Starch and glycogen are storage polysaccharides while cellulose and chitin are structural.

Section of Glycogen

Oligosaccharides                                                 

• Sugars containing 2 or 3 simple sugars attached to one another by covalent bonds known as glycosidic linkages ----> these bonds form by condensation reactions in which the H atom comes from a hydroxyl group on one sugar and _OH group comes from hydroxyl group on another

• Lactose, maltose and sucrose are oligosaccharides consisting 2 simple sugars while raffinose is an oligosaccharide consisting of 3 simple sugars

• They are covalently attached to proteins or membrane lipids and may be linear or branched

• Have many functions; for example they are commonly found on the plasma membrane of animal cells where they play a role in cell-cell recognition

• Selectin is an integral protein that that protrudes on outer surface of mammalian cells

    -----> it participates in cell-cell recognition and binding

Raffinose