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1 of 30© Boardworks Ltd 2008 Haggerston School Biology A-Level.

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Presentation on theme: "1 of 30© Boardworks Ltd 2008 Haggerston School Biology A-Level."— Presentation transcript:

1 1 of 30© Boardworks Ltd 2008 Haggerston School Biology A-Level

2 2 of 30© Boardworks Ltd 2008 All truths are easy to understand once they are discovered; the point is to discover them. Galileo Galilei

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5 5 of 30© Boardworks Ltd 2008 Structure of water Each hydrogen shares a pair of electrons with the oxygen. The oxygen has a greater affinity for electrons than the hydrogens, so it pulls the electrons closer. Water (H 2 O) consists of two hydrogen atoms covalently bonded to one oxygen atom. This makes the oxygen slightly negative (indicated by δ – ) and the hydrogens slightly positive (indicated by δ + ). This creates different charged regions, making water a polar molecule. Because it has two charged regions it is dipolar ° δ–δ– δ+δ+ δ+δ+

6 6 of 30© Boardworks Ltd 2008 Hydrogen bonds The slight negative charge on the oxygen atom makes it attract the slightly positive hydrogen atom of another water molecule. Many of the properties of water are due to its ability to form hydrogen bonds. The numerous hydrogen bonds in water make it a very stable structure. hydrogen bond

7 7 of 30© Boardworks Ltd 2008 Water as a solvent

8 8 of 30© Boardworks Ltd 2008 Properties and biological roles of water

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10 10 of 30© Boardworks Ltd 2008 Introducing carbohydrates Carbohydrates are a group of substances used as both energy sources and structural materials in organisms. All carbohydrates contain carbon, hydrogen and oxygen, with the general formula: C x (H 2 O) y. There are three main groups of carbohydrates: monosaccharides – these are simple sugars, with the general formula (CH 2 0) n, where n can be 3–7 disaccharides – these are double sugars, formed from two monosaccharides polysaccharides – these are large molecules formed from many monosaccharides.

11 11 of 30© Boardworks Ltd 2008 Glucose The structure of glucose can be represented in different ways: Glucose is an abundant and very important monosaccharide. It contains six carbon atoms so it is a hexose sugar. Its general formula is C 6 H 12 O 6. Glucose is the major energy source for most cells. It is highly soluble and is the main form in which carbohydrates are transported around the body of animals. straight chain ring ring (simplified)

12 12 of 30© Boardworks Ltd 2008 Alpha and beta glucose Glucose exists in different forms called structural isomers. Two common isomers are alpha glucose and beta glucose. alpha glucose beta glucose The only difference between these two isomers is the position of the –OH group attached to carbon 1. In alpha glucose it is below the carbon and in beta glucose it is above the carbon This minor structural difference has a major effect on the biological roles of alpha and beta glucose.

13 13 of 30© Boardworks Ltd 2008 Fructose and galactose Galactose is not as soluble as glucose and has an important role in the production of glycolipids and glycoproteins. Two other important hexose monosaccharides are fructose and galactose. fructose galactose Fructose is very soluble and is the main sugar in fruits and nectar. It is sweeter than glucose.

14 14 of 30© Boardworks Ltd 2008 Pentoses Pentose monosaccharides contain five carbon atoms. Like hexoses, pentoses are long enough to form a ring. Two important pentose molecules are the structural isomers ribose and deoxyribose. These are important constituents of RNA and DNA. ribosedeoxyribose The only difference between them is that ribose has one H atom and one –OH group attached to carbon 2, whereas deoxyribose has 2 H atoms and no –OH group

15 15 of 30© Boardworks Ltd 2008 The formation of disaccharides

16 16 of 30© Boardworks Ltd 2008 Maltose, sucrose and lactose Maltose (malt sugar) is formed from two glucose molecules joined by an alpha 1–4 glycosidic bond. Sucrose (table sugar) is formed from glucose and fructose joined by an alpha 1–4 glycosidic bond. Lactose (milk sugar) is formed from galactose and glucose joined by a beta 1–4 glycosidic bond.

17 17 of 30© Boardworks Ltd 2008 Benedicts test for reducing sugars

18 18 of 30© Boardworks Ltd 2008 Mono- and disaccharides

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20 20 of 30© Boardworks Ltd 2008 What are polysaccharides? Polysaccharides are polymers containing many monosaccharides linked by glycosidic bonds. Like disaccharides, polysaccharides are formed by condensation reactions. The major polysaccharides are starch and cellulose in plants, and glycogen in animals. Polysaccharides are mainly used as an energy store and as structural components of cells.

21 21 of 30© Boardworks Ltd 2008 The structure of starch

22 22 of 30© Boardworks Ltd 2008 Properties and uses of starch Starch is the major carbohydrate storage molecule in plants. Starch is produced from glucose made during photosynthesis. It is broken down during respiration to provide energy and is also a source of carbon for producing other molecules. It is usually stored as intracellular starch grains in organelles called plastids. Plastids include green chloroplasts (e.g. in leaves) and colourless amyloplasts (e.g. in potatoes).

23 23 of 30© Boardworks Ltd 2008 Iodine test for starch

24 24 of 30© Boardworks Ltd 2008 What is cellulose? Unlike starch, cellulose is very strong, and prevents cells from bursting when they take in excess water. Cellulose is another polysaccharide and is the main part of plant cell walls. It is the most abundant organic polymer. Cellulose consists of long chains of beta glucose molecules joined by beta 1–4 glycosidic bonds. The glucose chains form rope-like microfibrils, which are layered to form a network.

25 25 of 30© Boardworks Ltd 2008 The structure of cellulose

26 26 of 30© Boardworks Ltd 2008 What is glycogen? Animals do not store carbohydrate as starch but as glycogen. Glycogen has a similar structure to amylopectin, containing many alpha 1–6 glycosidic bonds that produce an even more branched structure. Glycogen is less dense and more soluble than starch, and is broken down more rapidly. This indicates the higher metabolic requirements of animals compared with plants. Glycogen is stored as small granules, particularly in muscles and liver.

27 27 of 30© Boardworks Ltd 2008 Polysaccharides: true or false?

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29 29 of 30© Boardworks Ltd 2008 Glossary

30 30 of 30© Boardworks Ltd 2008 Whats the keyword?

31 31 of 30© Boardworks Ltd 2008 Whats the carbohydrate?

32 32 of 30© Boardworks Ltd 2008 Multiple-choice quiz


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