- Monosaccharide composed of 6 carbons = hexose monosaccharide.
- Carbons are numbered clockwise beginning with 1C being to the right of the O within the ring.
- Alpha and Beta - OH group on 1C position.
- Polar and soluble in water.
- This is due to the hydrogen bonds thar form between the OH and H2O.
- Solubility is important because glucose needs to be dissolved in the cytosol of the cell.
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- Two alpha glucose side by side = two OH groups interact.
- Bonds are broken and new bonds are reformed in different places producing new molecules.
- Condensation reaction forms a glycosidic bond.
- 1-4 glycosidic bond.
- Maltose is formed - a disaccharide.
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- Fructose + Glucose = Sucrose.
- Glucose + Galactose = Lactose.
- Glucose + Glucose = Maltose.
- Fructose naturally occurs in fruit.
- Fructose is sweeter than glucose and glucose is sweeter than galactose.
- Pentose monosaccharides are sugars that contain five carbon atoms.
- TWO IMPORTANT PENTOSE SUGARS:
- RNA and DNA.
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STARCH AND GLYCOGEN
- Many alpha glucose molecules joined by glycosidic bonds.
- Chemical energy store.
- Amylose - polysaccharide:
- Alpha glucose joined by 1-4 glycosidic bonds.
- Glucose twists into a helix stabilised by hydrogen bonding within the molecule.
- Compact and less soluble than the glucose used to make it.
- Amylopectin - polysaccharide:
- 1-6 glycosidic bonds.
- Also bonds formed 1-4.
- Branched structure.
- 1-6 branching points occuring once every 25 subunits.
- Energy store in animals is glycogen.
- Forms more branches than amylopectin.
- Coiling and branching of these polysaccharides makes them very compact which is ideal for storage.
- Branching speeds up storing and releasing of the glucose molecules.
- Amylopectin and glycogen are insoluble, branched and compact.
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- Glucose is stored as starch by plants and as glycogen by animals and fungi until needed for respiration.
- Starch or glycogen undergo hydrolysis reactions.
- Reactions catalysed by enzymes.
- Break the glycosidic bonds.
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- Beta glucose molecules.
- Unable to join in the same way alpha moleules do.
- To overcome this, alternate beta glucose molecules are turned upside down.
- When a polysaccharide is formed from glucose in this way, it is unable to coil or form branches.
- A straight chain molecule is formed - Cellulose.
- Hydrogen bonds form microfibrils.
- Microfibrils join to make macrofibrils.
- Macrofibrils join to make fibres.
- Fibres are necessary for a healthy digestive system.
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BENEDICT'S TEST FOR REDUCING SUGARS
- Place sample in boiling tube.
- Add an equal volume of benedict's reagent.
- Heat the mixture gently in a water bath over 80 degrees C for five minutes.
- A positive result will be a brick-red precipitate.
- The more reducing sugar present, the less blue copper 2+ ions are left in the solution.
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BENEDICT'S TEST FOR NON-REDUCING SUGARS
- Carry out the reducing sugar test and you should obtain a negative result.
- E.G. Sucrose.
- Sucrose is boiled in dilute hydrochloric acid at above 80 degrees C in a water bath for 5 minutes.
- It is then neutralised with sodium hydrogen carbonate.
- Test with Benedict's again and then there should be a positive result.
- This is because the sucrose has been hydrolysed into glucose and fructose (both reducing sugars).
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IODINE TEST FOR STARCH
- Put a few drops of iodine dissolved in potassium iodide solution onto the sample. (Iodine solution).
- Yellow/brown to blue/black colour change is a positive result.
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