Biological molecules

• Carbohydrates are used to store and supply energy and can be structural.
• Monosaccharides are an example of a monomer that produces a polymer called polysaccharides.
• Amino acids are an example of a monomer that produces a polymer called proteins.
• Nucleotides are an example of a monomer that produces a polymer called nucleic acids (DNA/RNA).
• Polymers can be broken down into monomers by hydrolysis reactions, which involve water.
• Hydrogen bonds form where a slightly positively charged part of a molecule meets a slightly negatively charged part of another molecule, commonly between O and H atoms.
• Condensation reactions join monomers to make polymers.
• All biological molecules contain carbon.
• Monosaccharides are the simplest sugars and include Glucose, Fructose, Galactose, all with the formula C6H12O6.
• Reducing sugars include Glucose, Fructose, Galactose, all with the formula C6H12O6.
• Disaccharides are formed by a condensation reaction between two monosaccharides, with a glycosidic bond made.
• Monosaccharides and some disaccharides are reducing sugars, which can donate electrons to reduce another chemical.
• If no colour change occurs in the Benedict’s Test, a non-reducing sugar may be present.
• test for non-reducing sugars?

  1. add dilute HCl to sample and boil, causing any disaccharide to hydrolyse into its monosaccharides (acid hydrolysis).
  2. Add sodium hydrogencarbonate to neutralise the solution, then heat with Benedict’s solution.
  3. Colour change to orange-red indicates a non-reducing sugar was present.
• Polysaccharides are polymers containing many monosaccharides linked by glycosidic bonds.
• Polysaccharides are formed by condensation reactions.
• The major polysaccharides are starch and cellulose in plants, and glycogen in animals.
• Polysaccharides are mainly used as an energy store and as structural components of cells.
• Starch is used for energy storage in plants, while Glycogen is used for energy storage in animals.
• Beta glucose is the main monomer for cellulose, while alpha glucose is the main monomer for starch and glycogen.
• The unique properties of each amino acid are determined by the R group.
• There are 20 amino acids found within living organisms.
• Amino acids are comprised of a carboxyl (COOH) group, an amine (NH2) group and an R group.
• Peptide bonds form between -OH of carboxyl group and one -H of amino group.
• Many amino acids join together in a process called polymerisation to form a polypeptide.
• There are four orders of structure in proteins: primary, secondary, tertiary, and quaternary.
• A change in DNA gene sequence may lead to a change in the amino acid sequence of a polypeptide.
• Multiple polypeptide chains held together by bonds form the quaternary structure (4°) of a protein.
• A conjugated protein has a prosthetic (or non-protein) group added to it.
• The tertiary structure of a protein is determined by the primary structure and the secondary structure.
• The primary structure is the simplest level of structure, it is the sequence of amino acids in the polypeptide chain.
• test for lipids?

  1. add 5cm3 of ethanol
  2. add 5cm3 of water and shake gently
  3. a milky-white emulsion indicates the presence of a lipid.
• test for proteins

  1. add Biuret Reagent
  2. colour change from blue to purple indicates presence of proteins
• 2 amino acids form a dipeptide in a condensation reaction and a peptide bond is formed between them.
• A polypeptide is a long chain of amino acids joined together by peptide bonds.
• Proteins are made up of one or more polypeptides.
• The secondary structure (2°) of a protein is when the polypeptide chain folds or coils due to hydrogen bonds. This forms alpha helices (due to coiling) or beta pleated sheets (due to folding).
• The tertiary structure (3°) of a protein is when the polypeptide chain further folds into a 3D structure caused by bonding of atoms between R groups of different amino acids. Bonds could be ionic, hydrogen, or disulfide.
• Tertiary structure forms functional or structural proteins.
• This is beta glucose