Biological molecules

• Covalent bonding is when atoms share a pair of electrons in their outer shells. As a result the outer shell is filled and a more stable compound ( called a molecule ) is formed
• Ionic bonding is when ions with opposite charges attract one another. This electrostatic attraction is known as an ionic bond. Ionic bonds are weaker than covalent bonds
• Hydrogen bonding is when the electrons within a molecule are not evenly distributed but tend to spend more time at one position. This region is more negatively charged than the rest of the molecule
• Monomers can be linked together and forms long chains called polymers. this reaction is called polymerisation
• The monomers of a polymer are usually based on carbon
• Many polymers, such as polythene and polyesters, are industrially produced
• Other polymers, like polysaccharides, polypeptides and polynucleotides, are naturally made by living organisms
• The basic sub-unit of a polysaccharide is a monosaccharide or a single sugar like glucose
• Polynucleotides are formed from mononucleotide sub-units
• Polypeptides are formed by linking together peptides that have amino acids as their basic sub-unit
• During polymerisation each time a new sub-unit is attached a molecule of water is formed
• Reactions that produce water via polymerisation are called condensation reactions
• The formation of a polypeptide from amino acids and that of the polysaccharide starch from the monosaccharide glucose are both condensation reactions
• Polymers can be broken down through the addition of water
• Water molecules are used when breaking the bonds that link the sub-units of a polymer, thereby splitting the molecule into its constituent parts. This is a hydrolysis reaction
• Polypeptides can be hydrolysed into amino acids, and starch can be hydrolysed into glucose
• All the chemical processes that take place in living organisms are collectively called metabolism
• One mole contains the same number of particles as there are in 12g of carbon-12 atoms. 12g of carbon-12 atoms contain 6.022 x 10^23 , This is Avogadros constant
• Carbon atoms very readily form bonds with other carbon atoms, this allows a sequence of carbon atoms of various lengths to be built up, these form a 'backbone' which other atoms can be attached
• From these long chains of carbon a large number of different types and sizes of molecule can be made all based on carbon.
• carbon containing molecules are known as organic molecules
• Many organic molecules, including carbohydrates, are made up of a chain of individual molecules. Each individual molecule is called a monomer
• Examples of monomers include: monosaccharides, amino acids and nucleotides
• Monomers join together to form long chains called polymers
• Biological molecules like carbohydrates and proteins are often polymers
• In carbohydrates, the basic monomer unit is a sugar otherwise known as a saccharide
• A single monomer is called a monosaccharide , a pair of monosaccharides forms a disaccharide , and multiple monosaccharides form polysaccharides
• Monosaccharides are sweet tasting and are soluble substances that have the general formula (CH2O)n Where n can be any number from 3 to 7
• Examples of monosaccharides include glucose, galactose and fructose
• Glucose is a hexose (6-carbon) sugar and has the formula C6H12O6
• However, the atoms carbon, hydrogen and oxygen can be arranged in many different ways, e.g. glucose has 2 isomers: a-glucose and b-glucose
• All monosaccharides and some disaccharides (e.g. maltose) are reducing sugars
• Reduction is a chemical reaction involving the gain of electrons or hydrogen. A reducing sugar is therefore a sugar that can donate electrons to (or reduce) another chemical
• Label B-glucose

  A) H

  B) O

  C) OH

  D) HO

  E) H

  
• Label A-glucose

  A) H

  B) O

  C) H

  D) HO

  E) OH

  
• When a reducing sugar is heated with benedicts reagent it forms an insoluble red precipitate of copper oxide
• Add 2cm^3 of the food sample to a test tube. If the sample is not already in liquid form, grind it up in water. Add equal volume of benedicts reagent. Heat the mixture in a gently boiling water bath for five minutes
• If a reducing sugar is present in the benedicts test an orange-brown colour is formed
• Examples of monosaccharides forming disaccharides is:

  • Glucose joined to glucose forms maltose
  • Glucose joined to fructose forms sucrose
  • Glucose joined to galactose forms lactose
• When monosaccharides join together, a molecule of water is removed and the reaction is therefore called a condensation reaction. The bond formed is called a glycosidic bond