Carbohydrates
Most carbohydrates (and proteins/ nucleic acids) are polymers- large, complex molecules composed of long chains of monomers joined together. Monomers are small, basic molecular units, e.g. monosaccharides, amino acids and nucleotides |
Carbohydrates are made from monosaccharides. The monomers that they're made from are monosaccharides, e.g. glucose, fructose and galactose |
Glucose is a hexose sugar, a monosaccharide with six carbon atoms in each molecules. There are two types of alpha and beta- they're isomers. |
alpha vs beta glucose
joined by condensation, has glycosidic bonds
Glucogen
Glycogen is the main energy storage material in animals |
Animals store excess glucose as glycogen, a polysaccharide of alpha-glucose. It has a similar structure to amylopectin, but with more side branches so that stored glucose can be released quickly, important for energy release in animals. |
Also very compact so it is good for storage |
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Condensation Reactions
A condensation reaction is when two molecules join together with the formation of a new chemical bond and a water molecule is released when the bond is formed. Monosaccharides join together by condensation reactions, where a glycosidic bond forms as the water molecule is released. |
2 monosaccharides = disaccharides 2+ monosaccharides = polysaccharide |
sucrose= glucose and fructose, lactose= glucose and galactose, maltose= 2x alpha glucose |
Hydrolysis reactions
Polymers can be broken down into monomers by hydrolysis reactions. It breaks the chemical bind between monomers using a water molecule. Opposite of condensation. E.g. carbohydrates can be broken down into their constituent monosaccharides by hydrolysis |
Starch
The Main energy storage material in plants |
Cells get energy from glucose. Plants store excess glucose as starch. Starch is a mixture of two polysaccharides, amylopectin and amylose |
Amylose- a long,unbranched chain of a-glucose. The angles of the glycosidic bonds give it a coiled structure, making it compact, good for storage because more can be fitted in a small space |
Amylopectin- a long, branched chain of a-glucose. Its side branches allow enzymes that break down the molecule to get at the glycosidic bond easily, so glucose can be released quickly. |
Starch is insoluble in water and doesn't affect water potential, so it doesn't cause water to enter by osmosis., which would make them swell, this makes them good for storage. |
Iodine test for Starch- Add iodine dissolved in potassium iodide solution to test sample. If starch is present the sample changes from browny-orange to a dark blue black colour |
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Benedict's test for sugars
Sugar is a general term for monosaccharides and disaccharides. All sugars are either reducing or non-reducing |
Reducing Sugars- all monosaccharides and some disaccharides |
Non-reducing sugar e.g. sucrose, has to be broken down first to be tested. |
Add Benedict's reagent (which is blue) to a sample and heat it in a water bath that's been bought to boil. If it's positive, it will form a coloured precipitate |
Add dilute hydrochloric acid to solution and gently heating in a water bath that's been bought to a boil. You then neutralise with sodium hydrogen carbonate. |
blue-> green -> yellow -> orange ->brick red |
Then carry out reducing sugar test |
The higher the concentration the further the colour change goes. Can use to copare, but better if filter the solution and weigh the precipitate |
Cellulose
Made of long, unbranched chains of beta-glucose |
When beta-glucose molecules bind, they form straight cellulose chains. These are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres means cellulose provides structural support for cells |
Cellulose
Made of long, unbranched chains of beta-glucose |
When beta-glucose molecules bind, they form straight cellulose chains. These are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres means cellulose provides structural support for cells |
Cellulose
Made of long, unbranched chains of beta-glucose |
When beta-glucose molecules bind, they form straight cellulose chains. These are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres means cellulose provides structural support for cells |
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