Biological molecules

• Monomers are small units which are the components of larger molecules, examples include monosaccharides such as glucose, amino acids and nucleotides
• Polymers are molecules made from many monomers joined together
• Monomers are joined by a chemical bond in a condensation reaction whereby a water molecule is eliminated
• Hydrolysis is the opposite of a condensation reaction and is when water is added to break a chemical bond between two molecules
• Carbohydrates consist only of carbon, hydrogen, and oxygen and are long chains of sugar units called saccharides
• A single monomer is called a monosaccharide with a pair of monomers being called a disaccharide
• Combining many monosaccharides results in the formation of a polysaccharide joined together with a glycosidic bond formed in a condensation reaction
• Glucose is a monosaccharide containing six carbon atoms in each molecule and is the main substrate for respiration
• Common monosaccharides include glucose, galactose, and fructose
• Disaccharides are formed by the condensation of two monosaccharides
• Examples of common disaccharides include Maltose, Sucrose, and Lactose
• Polysaccharides are formed from many glucose units joined together and include Glycogen, starch, and cellulose
• Glycogen is the main energy storage molecule in animals and is formed from many molecules of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds
• Starch stores energy in plants and is a mixture of two polysaccharides called amylose and amylopectin
• Cellulose is a component of cell walls in plants and is composed of long, unbranched chains of beta glucose joined by glycosidic bonds
• Benedict’s reagent can be used to test for the presence of reducing sugars
• A chemical test for starch is iodine/potassium iodide
• Triglycerides are lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions
• Saturated lipids don't contain any carbon-carbon double bonds, while unsaturated lipids contain carbon-carbon double bonds
• Phospholipids have a phosphate-containing group and form micelles when in contact with water
• An emulsion test can be used to test for the presence of lipids
• Amino acids are the monomers from which proteins are made
• A dipeptide contains two amino acids and polypeptides contain three or more amino acids
• Structure of proteins is determined by the order and number of amino acids, bonding present, and the shape of the protein
• Protein structure:

  • Primary structure: order and number of amino acids, determines protein function
  • Secondary structure: shape of amino acid chain, alpha helix or beta pleated sheet formed by weak hydrogen bonds
  • Tertiary structure: 3D shape formed by twisting and folding, maintained by disulfide bridges, ionic bonds, and hydrogen bonds
  • Proteins can be globular (enzymes) or fibrous (keratin)
• Biuret Test for Proteins:

  • Test for presence of peptide bonds in proteins
  • Positive result: purple coloration, indicates presence of peptide bond and protein
• Enzymes:

  • Increase rate of reaction by lowering activation energy
  • Tertiary structured globular proteins with active site specific to substrates
  • Enzyme-substrate complex formed in induced fit model
• Factors affecting enzyme-controlled reactions:

  • Temperature: rate increases up to optimum, then decreases
  • pH: affects enzyme shape, different enzymes work at different optimum pH
  • Enzyme concentration: rate increases with concentration, then levels off
  • Substrate concentration: rate increases with concentration, then levels off
  • Competitive reversible inhibitors: decrease rate by blocking active sites
  • Non-competitive reversible inhibitors: decrease rate by altering enzyme shape
• Structure of DNA and RNA:

  • DNA and RNA are polymers of nucleotides
  • DNA nucleotide: deoxyribose sugar, phosphate group, adenine, cytosine, guanine, thymine
  • RNA nucleotide: ribose sugar, phosphate group, adenine, cytosine, guanine, uracil
  • DNA is a double helix with hydrogen bonds between complementary bases
  • DNA replication is semi-conservative
• ATP:

  • Adenosine triphosphate, releases energy when hydrolysed to form ADP and phosphate
  • Inorganic phosphate can phosphorylate other compounds
  • ATP is immediate source of energy, not stored in large quantities
• Water:

  • Polar molecule with hydrogen bonding
  • Metabolite in condensation and hydrolysis reactions
  • Solvent for gases, enzymes, waste products
  • High heat specific capacity, acts as buffer
  • Large latent heat of vaporisation, provides cooling effect
• Inorganic ions:

  • Hydrogen ions determine pH
  • Iron ions in haemoglobin
  • Sodium ions in co-transport
  • Phosphate ions in DNA and ATP
• Enzymes are tertiary structure proteins
• Enzymes catalyze different reactions
• Enzymes are relatively large molecules compared to other biological molecules
• Only a small part of an enzyme, the active site, is involved in catalyzing the reaction
• The active site is where the substrate, which is complementary in shape, will bind to form enzyme-substrate complexes
• Enzymes lower the activation energy required for a reaction to occur
• The tertiary structure of a protein is determined by the sequence of amino acids in the primary structure
• The unique 3D shape of the tertiary structure creates a unique shape active site that is complementary to one particular substrate