CORE PRINCIPLES Biological molecules

CARBOHYDRATES: Learning objective to be able to: Identify the elements that make up carbohydrates To describe how monosacharides are the basic molecular units of carbohydrates. Explain how the condensation of monosacharides forms disacharides

Which elements make up carbohydrates? Carbon, hydrogen and oxygen What are carbohydrates needed for? Energy Where can we find carbohydrates? Pasta, potatoes, bread etc Give the chemical formula of a well known carbohydrate C6H12O6 - glucose

Carbohydrates include monomers, dimers and polymers. three properties common to all monosaccarides and disaccharides Sweet tasting, soluble, crystalline, white

Monosaccharides These all have the formula (CH2O)n, where n can be 3-7. The most common and important monosaccharide is glucose, where n=6 This is a six-carbon or hexose sugar, so has the formula C6H12O6. Its structure is: CH2OH Or more simply:

Isomers of glucose They have the same molecular formula (C6H12O6), but different structural formulae. These isomers include Fructose Galactose Mannose

α - Glucose β- Glucose CH2OH H H C O C OH H C C C OH OH H OH

α- Glucose Galactose CH2OH OH H H C O C OH H C C C OH H OH H OH

Fructose

Pentose monosaccharides Common five-carbon, or pentose sugars (where n = 5, C5H10O5) include Ribose Deoxyribose (found in nucleic acids and ATP) Ribulose

Disaccharides Disaccharides are formed when two monosaccharides are joined together by a glycosidic bond. The reaction involves the formation of a molecule of water (H2O)

glucose + glucose = maltose OH O CH2 OH OH O CH2 OH OH OH glucose + glucose = maltose

This shows two glucose molecules joining together to form the disaccharide maltose. Because this bond is between carbon 1 of one molecule and carbon 4 of the other molecule it is called a 1-4 glycosidic bond. Bonds between other carbon atoms are possible, leading to different shapes, and branched chains.

Polymerisation When molecules are joined together this is called polymerisation Because a small molecule is lost, (usually water) this is called a condensation reaction The reaction that joins two monosaccharides together is therefore called a condensation polymerisation reaction

Hydrolysis In general: polymerisation reactions are condensations Breaking apart the disaccharide would require a water molecule This is called a hydrolysis reaction In general: polymerisation reactions are condensations breakdown reactions are hydrolysis

Three common disaccharides Maltose (or malt sugar) is glucose 1-4 glucose. Sucrose (or cane sugar) is glucose 1-2 fructose. Lactose (or milk sugar) is galactose 1-4 glucose. Maltose (or malt sugar) is glucose 1-4 glucose. It is formed on digestion of starch by amylase, because this enzyme breaks starch down into two-glucose units. Brewing beer starts with malt, which is a maltose solution made from germinated barley. Sucrose (or cane sugar) is glucose 1-2 fructose. It is common in plants because it is less reactive than glucose, and it is their main transport sugar. It is the common table sugar that you put in your tea. Lactose (or milk sugar) is galactose 1-4 glucose. It is found only in mammalian milk. It is the main source of energy for infant mammals.

Summary of Carbohydrates Carbon atoms bond strongly to each other forming chains and rings. Carbohydrates include monosaccharides, disaccharides and polysaccharides. They can act as an energy source or provide structural support. Monosaccharides include glucose, fructose and galactose. They have the same chemical formula but different chemical structures ~ we call them isomers. Monosaccharides can become linked together by a glycosidic bond to form disaccharides such as maltose, sucrose and lactose, and polysaccharides, such as starch and cellulose. Polysaccharides can perform structural roles, for example cellulose in plant cells, and energy storage roles, for example starch in plants and glycogen in animals.