Glycolysis

• Glucose


  Not just a molecule to make cellular energy, the carbons and accompanying atoms are the ingredients for energy storage (provide the three examples glycerol, hexokinase, nucleotides), formation of nucleotides by the pentose phosphate pathway (forming ribose), or synthesis of structural polymers [cellulose in plants or bacteria] or the extracellular matrix in animal cells

  
• Glycolysis


  1. A metabolic pathway of 10 steps that turns a hexose into 2 trioses in the form of pyruvate

  2. The first five steps are the preparatory phase where 2 molecules of ATP are invested

  3. The last five steps are the payoff phase where 2 molecules of ATP are produced from 2 molecules of glyceraldehyde 3-phosphate

  
• Preparatory phase


  • Steps 1-5
• Payoff phase


  • Steps 6-10
• The source of the phosphate groups in the preparatory phases is ATP
• The source of the phosphate added in step 6 of the payoff phase is 1,3-bisphosphoglycerate
• The bidirectional arrows suggest that the reactions in the pathway are reversible
• Kinase enzymes


  Enzymes moving phosphate groups from ATP to glycolytic molecules or from the phosphorylated intermediates to ADP
• The dihydroxyacetone phosphate (DHAP) from the preparatory phase can be converted to glyceraldehyde 3-phosphate by the enzyme triose phosphate isomerase

  
• A mutant yeast strain with a shorter glycolytic pathway would not be beneficial to the cell as it would produce less ATP
• Fermentation


  The conversion of pyruvate to ethanol in yeast

  
• Fermentation


  The conversion of pyruvate to lactate in respiring mammals

  
• Decarboxylation


  The conversion of pyruvate to acetyl-CoA before entering the citric acid cycle

  
• Fructose


  Enters glycolysis as fructose 1-phosphate
• Mannose


  Enters glycolysis as mannose 6-phosphate
• NAD+


  The cofactor required in the reaction where Glyceraldehyde 3-phosphate (G3P) becomes 1,3-bisphosphoglycerate

  
• Lactate


  The fermentation byproduct in mammals
• Ethanol


  The fermentation byproduct in yeast and other microorganisms
• There is no energetic advantage to producing lactate or ethanol, as both produce less ATP than aerobic respiration
• The advantage of producing lactate or ethanol is that it allows glycolysis to continue by regenerating NAD+ for the payoff phase

  
• The pathway further supported by the oxidation of NADH is the citric acid cycle
• Glucose fermentation is dependent on inorganic phosphate (Pi) because Pi is required for the conversion of 3-phosphoglycerate to 2-phosphoglycerate in the payoff phase of glycolysis

  
• CO2 production is a good indicator of fermentation because it is a byproduct of the conversion of pyruvate to ethanol

  
• The fermentation happening in the described experiment is ethanol fermentation
• Gluconeogenesis


  The pathway where glucose is made from pyruvate, lactate, or oxaloacetate

  
• Enzymes associated with the regulated (nonreversible) steps of glycolysis

  • Hexokinase
  • Phosphofructokinase-1
  • Pyruvate kinase
• Enzymes associated with the regulated (nonreversible) steps of gluconeogenesis

  • Glucose-6-phosphatase
  • Fructose 1,6-bisphosphatase 1
  • PEP carboxykinase
  • Pyruvate carboxylase

  
• Gluconeogenesis occurs in the liver and kidneys
• The delta G of the three glycolytic reactions is negative, making them irreversible
• The delta G of the reversible reactions in glycolysis or gluconeogenesis is approximately 0

  
• Pentose phosphate pathway


  An alternative pathway of glucose oxidation that produces nucleotides after forming the pentose ribose when carbon #1 is removed from glucose
• The carbon lost from glucose in the pentose phosphate pathway leaves as a molecule of CO2
• In the diagram, carbon #1 is colored blue
• The CO2 molecule leaving near the end of the pentose phosphate pathway is also blue

  
• The molecule that accepts the hydrogen lost from glucose 6-phosphate in the pentose phosphate pathway is NADP+
• G6P dehydrogenase


  The enzyme that catalyzes the first oxidation step in the pentose phosphate pathway

  
• 1. phosphogluconate dehydrogenase


  The enzyme that catalyzes the second oxidation step in the pentose phosphate pathway

  
• The dehydrogenase enzymes in the pentose phosphate pathway are involved in removing hydrogens