Carbohydrates

• Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides.
• What are the three types of saccharides?

  Monosaccharides

  Disaccharides

  Polysaccharides
• Monosaccharides can join together to form disaccharides and polysaccharides by glycosidic bonds which are formed in condensation reactions.
• Glucose is a monosaccharide containing six

  carbon atoms in each molecule, it is the main

  substrate for respiration therefore it is of

  great importance.

  
• Maltose is a disaccharide formed by condensation of two glucose molecules
• Sucrose is a disaccharide formed by condensation of glucose & fructose
• Lactose is a disaccharide formed by condensation of glucose & galactose
• Glycogen and starch which are both formed by the condensation of alpha glucose
• Cellulose formed by the condensation of beta glucose
• Glycogen is the main energy storage molecule in animals and it’s formed from many

  molecules of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds
• Glycogen has a large

  number of side branches meaning that glucose & therefore energy, can be released quickly.
• Starch stores energy in plants and it is a mixture of two polysaccharides called amylose and

  amylopectin
• Amylose – amylose is an unbranched chain of glucose molecules joined by 1, 4

  glycosidic bonds, as a result of that amylose is coiled and thus it is a very compact

  molecule meaning it can store a lot of energy
• Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1,

  6 glycosidic bonds, due to the presence of many side branches it is rapidly digested

  by enzymes therefore energy is released quickly
• Cellulose is a component of cells wells in plants and it’s composed of long, unbranched

  chains of beta glucose which are joined by glycosidic bonds.
• Microfibrils are strong threads

  which are made of long cellulose chains joined together by hydrogen bonds and they

  provide structural support in plants cells
• What are the two types of lipids?

  Saturated

  Unsaturated
• Saturated lipids such as those found in

  animal fats – saturated lipids don’t contain any

  carbon-carbon double bonds

  
• Unsaturated lipids which can be found in

  plants – unsaturated lipids contain carbon-carbon

  double bonds and melt at lower temperatures than

  saturated fats

  
• The greater the number of unsaturated bonds, the weaker the intermolecular bonds resulting

  in lower melting point, and as a result of that saturated fats which don’t contain any double

  bonds are solid at liquid temperature and unsaturated lipids are liquid at room temperature.
• Triglycerides are lipids made of one molecule of

  glycerol and three fatty acids joined by ester

  bonds formed in condensation reactions.
• There are many different types of fatty acids, they vary in chain length, presence and number of double bonds.
• Triglycerides are used as

  energy reserves in plant and animal cells.
• In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-

  containing group.
• Phosphate heads are hydrophilic and the tails are hydrophobic and as a result phospholipids form micelles when they are in contact with water as heads are on the

  outside as they are attracted to water and tails are on the inside as they move away from water.