Carbohydrates
Teacher recommended
?- Created by: Buffya
- Created on: 25-05-13 13:56
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- Carbohydrates
- Simple sugars
- Functions in organisms
- Energy source - released from glucose during respiration
- Energy store e.g Starch
- Structure e.g. cellulose
- Monosaccharides
- 5 carbon monosaccharides are known as pentose sugars e.g. Deoxyribose
- All are soluble in water, sweet tasting and form crystals
- 3 carbon monosaccharides are known as triose sugars
- 6 carbon monosaccharides are known as hexose sugars.
- Glucose
- Hexose sugar
- Can be drawn in a chain or ring structure
- In the ring structure there are two different isomers ALPHA glucose and BETA glucose
- In alpha-glucose, the OH is below the plane of the ring
- In the beta-structure, the OH IS above the plane of the ring
- Joining and splitting
- Two monosaccharides can be joined together in a CONDENSATION reaction
- A covalent glycosidic bond is made with the elimination of water
- The reverse reaction is a hydrolysis reaction which uses water to break the glycosidic bond
- Two monosaccharides can be joined together in a CONDENSATION reaction
- Functions in organisms
- Carbohydrates make up a group of molecules containing carbon, hydrogen and oxygen in the ratio Cn(H2O)n
- Energy storage
- The breaking of glucose into simpler molecules of carbon dioxide and water in respiration releases energy in the form of ATP
- Each step is driven by a specific enzyme. Animals and plants have enzymes that break down alpha-glucose only due to the different structure
- A polysaccharide formed from alpha glucose is amylose
- The long chains of amylose coil into a spring due to the formation of the glycosidic bonds
- Iodine molecules can be trapped in the coils of the spring which causes it to change from yellow/brown to blue/black
- The bond is called a 1,4-glycosidic bond
- Insoluble in water
- Hold glucose in chains so they can easily be broken off for respiration
- The long chains of amylose coil into a spring due to the formation of the glycosidic bonds
- In plants
- Starch is a mixture of long, straight-chain amylose and branched amylopectin
- Stored in chloroplasts and elsewhere in membrane-bound starch grains
- Starch is a mixture of long, straight-chain amylose and branched amylopectin
- In animals
- Glycogen differs from starch in that the 1,4-glycosidic chains are shorter and have many more branches
- More compact so forms glycogen granules - especially in liver and muscle cells
- Glycogen differs from starch in that the 1,4-glycosidic chains are shorter and have many more branches
- The breaking of glucose into simpler molecules of carbon dioxide and water in respiration releases energy in the form of ATP
- Structural units
- Beta glucose can be condensed to form long and straight chained polymer chains called cellulose chains
- Cellulose is found in plants only
- As the glucose monomers contain many OH groups, many hydrogen bonds can be formed
- About 60 - 70 cellulose molecules become cross-linked to form microfibrils
- These in turn can form hydrogen bonds to form macrofibrils which are embedded in pectin to form cell walls
- About 60 - 70 cellulose molecules become cross-linked to form microfibrils
- As the glucose monomers contain many OH groups, many hydrogen bonds can be formed
- Cellulose is found in plants only
- Other structural carbohydrate polymers include chitin in exoskeletons and peptidoglycan in bacterial cell walls
- Structure and function of cell wall
- The wall prevents bursting and the cell becomes turgid instead, for support
- Arrangement of macrofibrils allow water to move in and out of the cell
- Can be reinforced with other substances to proved extra support or to make the walls waterproof
- The macrofibril arrangement in stomata result in the opening and closing of a stoma
- Beta glucose can be condensed to form long and straight chained polymer chains called cellulose chains
- Simple sugars
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