SUGAR

• What is a single sugar unit called?

  A monosaccharide, a simple sugar consisting of one monosaccharide unit, eg. glucose.
• What are two monosaccharide units called?

  A disaccharide, eg. sucrose.
• What are more than two monosaccharide units called?

  A polysaccharide, eg. glycogen.
• What is glucose?


  A hexose monosaccharide of 6 carbons that is polar, and soluble in water.
• How is maltose made?

  Two alpha glucose molecules next to each other, whose two hydroxyl groups interact, causing bonds to be broken and new ones reformed in different places producing new molecules. A covalent, glycosidic bond forms between the two glucose molecules, and a water molecule is formed as a product. Carbon one joins to carbon two, making a one, four glycosidic bond; two monosaccharides, a disaccharide.
• What does fructose (hexose monosaccharide) and glucose form?

  Lactose, a disaccharide (milk).
• What does galactose (hexose monosaccharide) and glucose form?

  Sucrose, a disaccharide (sugar).
• What are pentose monosaccharides?

  Sugars containing five carbon atoms, containing both RNA ribose and DNA deoxyribose; both of which are pentose sugars.
• What is starch?


  Starch is the primary chemical energy store in plants, a complex carbohydrate made up of many alpha glucose molecules joined by glycosidic bonds. It consists of two polysaccharides, amylose and amylopectin formed by one, four glycosidic bonded alpha glucoses. The angle of the bonds of amylose causes a long chain of twists to form a helix that is stabilised by hydrogen bonding, making it more compact and less soluble. Some of the bonds in amylopectin are formed through condensation reactions between one and six on two glucose molecule, forming a branch structure.
• What is glycogen?


  A storage form of glucose in animals and fungi that forms more branches than amylopectin, and so are more compact storage for mobile animals. Branching also allows for free branch ends to add or remove a glucose, speeding up the process of storing and releasing glucose.
• What is cellulose?


  A complex carbohydrate that is the main structural component of plant cell walls; makes hydrogen bonds with each other to form microtubules which combine to form fibres that are strong and insoluble for walls, and a healthy digestive system. Consists of beta glucose that forms a polymer by joining to an alternative beta glucose that is turned upside down; when a polysaccharide is formed, it's unable to coil or branch, forming a straight cellulose chain.
• Hydrolysis reactions in the release of glucose?

  When glucose is needed for respiration, the biochemicals in stored nutrients are converted into useable energy, done through the addition of a water molecule.
• How to test for carbohydrates?

  Benedict's test for reducing sugars, sugars that can donate electrons or reduce another chemical.
• How would we test for reducing sugars?

  1. Place your sample in a boiling tube, and if not in liquid form then grind it.
  2. Add equal volumes of benedict reagent, and heat the mixture in a water bath for five minutes.
• What results will you find for a benedict test?


  Reducing sugars will react with the copper ions in benedict solution, resulting in the addition of electrons to blue copper ions (Cu2+), reducing them to brick red copper ions (Cu+). So when a reducing sugar is mixed with the reagent, a red precipitate is formed, indicating a positive result. The more red precipitate formed and less blue copper ions (Cu2+) left in the solution, the more reducing sugars present.
• How to test for starch?

  Iodine.
• What is the process of testing for starch?

  1. Drop a few drops of iodine dissolved in potassium iodine solution and mix with the sample.
  2. If the solution changes from yellow/brown to purple/black then starch is present.