Biochemistry

• Give two main reasons why carbohydrates are so important

  Carbohydrates act as main energy sources and structural components
• What elements do carbohydrates contain and what is their general formula?

  Carbon, Hydrogen, Oxygen.

  Cx(H2O)y
• How can carbohydrates be classified?

  Sugars- Monosaccharides (glucose, fructose and galactose)

  Disaccharides (maltose, sucrose and lactose)

  Polysaccharides- Storage (starch and glycogen)

  Structural (cellulose and chitin)
• Explain what is meant by a monosaccharide and why this type of molecule is important

  Monosaccharide- single sugar unit building block usually consisting of 3 to 7 carbons, smallest carbohydrates.

  Important as they are a good source of energy.
• Monosaccharides are classified according to the number of carbon atoms. Give 3 examples

  Triose sugars, glyceraldehyde 3 phosphate

  Pentose sugars, ribose and deoxyribose

  Hexose sugars, glucose
• What are the functions of Triose sugars

  intermediate in respiration and photosynthesis
• What are the functions of Pentose sugars

  Present in DNA and RNA
• What are the functions of hexose sugars

  Glucose (example of hexose sugar) is used as a respiratory substrate
• What two reactive/functional groups do all monosaccharides contain?

  Carbonyl group (C=O) and a Hydroxyl group (OH)
• Describe with the help of structural formula diagrams, the difference between a-glucose and b-glucose

  ABBA- alpha below, beta above

  
  

  In ALPHA GLUCOSE the C1 hydroxyl lies below the plane of the ring. (storage)

  In BETA GLUCOSE the C1 hydroxyl lies above the plane of the ring. (structural)

  
• What is the difference between the L and D-forms of glucose?

  L glucose, the OH lies to the left on C5

  D glucose, the OH lies to the right on C5
• Describe how two monosaccharide molecules can combine together to form a disaccharide by a condensation reaction

  Water comes off when the hydrogen of one monosaccharide reacts with the hydroxyl group of another.
• Why are condensation reactions so called?

  because water is produced
• Give 3 examples of common disaccharides and describe what monosaccharides they are composed of

  Maltose- glucose+glucose

  Sucrose-glucose+fructose

  Lactose- glucose+galactose
• Describe how you would determine whether a particular sugar is reducing or non reducing.

  Benedicts reagant (blue) when heated with reducing sugars produce a red insoluble precipitate with copper(II)oxide.
• Which sugar will not give a positive test with Benedict's reagent?

  sucrose
• Describe the structure of a starch molecule

  Amylose- straight chained, forms into a helix

  Amylopectin- branched, wraps around amylose
• What is the energy storage polysaccharide found in animals?

  Glycogen
• Describe the features of a starch molecule which make it a suitable for storage in cells

  Compact

  Insoluble

  Does not affect the water balance of the cell

  Accessible to enzymes when needed
• What is glycogen composed of?

  Alpha glucose molecules, highly branched
• Describe the structure of a cellulose molecule

  It consists of many thousands of glucose molecules joined by a beta (1-4) glycosidic bonds (identical to that in cellobiose). Successive glucose units are inverted with respect to one another. This allows hydrogen bonding to take place between parallel chains.
• Describe the features of a cellulose molecule which make it a suitable material for constructing cell walls.

  Hydrogen bonds between sheets give rigidity and strength.