Monomers and Polymers

• Monomers are small units which are the components of larger molecules, examples of include monosaccharides (such as glucose), amino acids and nucleotides
• Polymers are molecules made from monomers joined together
• A condensation reaction is a reaction which joins monomers by chemical bonds and it involves the elimination of a water molecule
• Hydrolysis is the opposite of condensation and it’s when water is added to break a chemical bond between two molecules.
• Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides
• There are three types of saccharides - monosaccharides, disaccharides and 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.
• Glucose has two isomers – alpha and beta glucose with following structures:
• Disaccharides:

  • 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
• Polysaccharides are formed from many glucose units joined together and include:

  • 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 and therefore energy, can be released quickly.
• Moreover, glycogen is a relatively large but compact molecule thus maximising the amount of energy it can store.
• 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.
• Lipids are biological molecules which are only soluble in organic solvents such as alcohols.
• There are two types of lipids:

  • 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
• Also, some triglycerides contain a mix of different fatty acids. 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.