Enzymes chp3

• Biochemical pathways


  A series of linked biochemical reactions that start with an initial reactant that is converted in a stepwise fashion to a final product
• Enzyme


  A protein that acts as a biological catalyst, speeding up reactions without being used up
• Metabolism


  The total of all chemical reactions occurring in an organism
• Examples of biochemical pathways and enzymes involved

  • Cellular respiration - Glycolysis (Phosphofructokinase), Krebs cycle (Malate dehydrogenase), Electron transport chain (Cytochrome c oxidase)
  • Nucleic acid pathways - DNA replication (DNA polymerase), Transcription of mRNA (RNA polymerase), mRNA translation to protein (Aminoacyl tRNA synthetase)
  • Photosynthesis - Light-dependent stage (Water-splitting enzyme), Light-independent stage (Rubisco)
• Reactant


  A substance that is changed during a chemical reaction
• Product


  The compound that is produced in a reaction
• Substrate


  A compound on which an enzyme acts
• Anabolic pathways


  • Assemble simple molecules into more complex molecules
  • Are energy-requiring or endergonic
• Anabolic pathways


  • Photosynthesis
  • Assembling amino acids into proteins
  • Building macromolecules of glycogen from glucose
  • Building starch from sugars
  • Building DNA from nucleotides
• Catabolic pathways


  • Break down complex molecules into more simple molecules
  • Are energy-releasing or exergonic
• Catabolic pathways


  • Aerobic cellular respiration
  • Breakdown of fatty acids to carbon dioxide
• Catabolic reactions


  Produce a net release of energy as the energy level of the initial reactants is higher than that of the final products
• Anabolic reactions


  Require energy, so the energy level of the initial reactants is lower than that of the final products
• In cells, catabolic and anabolic reactions are constantly operating, but do not operate in isolation. Instead, reactions are coupled so that the energy released by catabolic reactions can be transferred to drive energy-requiring anabolic pathways.
• Biochemical pathway


  A series of chemical reactions that occur within a cell
• Biochemical pathways


  • Occurs in green plants and algae only
  • Involved in cellular respiration
  • Requires an overall input of energy to proceed
  • Involves the transformation of the radiant energy of sunlight to the chemical energy of sugars
• Anabolism


  Metabolic pathways that build up larger molecules from smaller ones
• Catabolism


  Metabolic pathways that break down larger molecules into smaller ones
• Endergonic reaction


  A reaction that requires an input of energy to proceed
• Exergonic reaction


  A reaction that releases energy
• Enzyme-catalysed reaction


  A reaction that is sped up by the presence of an enzyme
• Biochemical reaction


  A single chemical reaction that is part of a larger biochemical pathway
• All enzymes do not have a similar reaction rate
• Exergonic reactions include photosynthesis
• The reactant is not the final molecule produced in a biochemical pathway
• Some enzymes are only active in specific cells
• Photosynthesis uses energy from the Sun to allow for the production of glucose
• Cellular respiration breaks down glucose to release energy in the form of ATP
• Photosynthesis


  Endergonic process
• Cellular respiration


  Exergonic process
• Phosphofructokinase increases the rate of the reaction it catalyses
• Starch is the substrate in the reaction catalysed by amylase
• Sucrose is a disaccharide formed from glucose and fructose
• The production of sucrose is an exergonic reaction
• Sucrose is a product, not a reactant, of the reaction
• A molecule of fructose does not contain more stored energy than a molecule of sucrose
• In Biochemical Pathway 1, if the production of enzyme 3 stops there would be continuous production of isoleucine
• In Biochemical Pathway 2, if the production of enzyme 3 stops there would not be continuous production of arginine
• In Biochemical Pathway 1, providing all enzymes are present, the production of isoleucine would be continuous if there was a continuous supply of threonine
• In Biochemical Pathway 2, providing all enzymes are present, the production of arginine would not be continuous if there was a continuous supply of substrate