Glycolysis

• Glycolysis

  • This stage involves the breakdown of the six-carbon sugar glucose and the production of pyruvate and ATP molecules
• Glycolysis happens in the cell cytoplasm.
• Compound of Glucose

  C6H12O6
• In glycolysis, the oxidation of glucose results in the release of

  electrons.
• after the release of electrons, these electrons are picked up by NAD+, which is then reduced to NADH
• NAD stands for...

  nicotinamide adenine dinucleotide
• ENZYMES

  • fastens the process
• Gly - sugar
• olysis - break
• TWO TYPES OF GLYCOLYSIS

  1. Energy-Investment Phase
  2. Energy-Harvesting Phase
• Energy-Investment Phase

  • investing ATP molecules
• Energy-Harvesting Phase

  • harvesting ATP molecules
• ATP

  • adenosine triphosphate
  • energy
  • consists of a nitrogenous base which is adenine
• Adenine - ribose sugar (5 carbon ring) - 3 carbon

  • nitrogenous
• ADP

  • adenosine diphosphate
• PHOSPHORYLATION

  • add a phosphate group to a particular molecule
• Glycolysis happens in both aerobic and anaerobic conditions
• main product of glycolysis

  • pyruvate
• the pyruvate, can

  either undergo the Krebs cycle or fermentation.
• Reactant of glycolysis

  • glucose
• The energy-investment phase starts with one glucose molecule with an investment of ATP molecules.
• STEP 1

  • the glucose molecule is added with phosphate from an ATP, which results in the formation of glucose-6-phosphate
  • One phosphate group is used in this process; thus, ATP becomes ADP (adenosine diphosphate).
  • catalyzed by an enzyme, hexokinase
• STEP 2

  • Glucose-6-phosphate is catalyzed by phosphoglucose isomerase which then turns to fructose-6-phosphate
  • Glucose-6-phosphate and fructose-6-phosphate are isomers —molecules with the same chemical formula but differ in structure.
• STEP 3

  • phosphorylation of fructose-6-phosphate by adding one phosphate group from an ATP molecule.
  • turns to fructose-1,6-bisphosphate, catalyzed by phosphofructokinase
• STEP 4

  • splitting fructose-1,6-bisphosphate into isomers DHAP (dihydroxyacetone phosphate) and G3P (glyceraldehyde-3-phosphate).
  • catalyzed by an enzyme called aldolase.
• STEP 5

  • transformation of DHAP into G3P
  • catalyzed by triosephosphate isomerase
  • Isomerase - an enzyme that causes a molecule to transform into its isomer
• The energy-investment phase of glycolysis utilizes a total of 2 ATP molecules for every glucose molecule.
• Phosphorylation of these molecules needs to happen to prevent them from leaving the cell.
• During the energy-harvesting phase, ATP molecules and NADH are formed.
• There are two G3P molecules that will enter the energy-harvest phase.
• STEP 6

  • involves the oxidation and phosphorylation of these G3P molecules
  • catalyzed by an enzyme called glyceraldehyde-3-phosphate dehydrogenase
  • During the oxidation of G3P, hydrogen atoms are released and picked up by NAD+ (nicotinamide adenine dinucleotide) to form NADH.
  • During the phosphorylation, a free inorganic phosphate from the cell cytosol is combined to G3P to form the 1,3-bisphosphoglycerate (BPG).
• STEP 7

  • involves the release of the phosphate molecule from BPG, which now becomes 3-phosphoglycerate (3-PGA)
  • catalyzed by the enzyme phosphoglycerate kinase
  • The phosphate released from BPG will be picked up by ADP (adenosine diphosphate) to form ATP
• STEP 8

  • the 3-PGA becomes 2-phosphoglycerate through an enzyme called phosphoglycerate mutase
  • This enzyme transfers a phosphate group from the third carbon of 3-PGA to its second carbon, which results in the 2-phosphoglycerate (2-PGA).
• STEP 9

  • 2-PGA becomes phosphoenolpyruvate (PEP), which is accomplished by the removal of water from 2-PGA through an enzyme called enolase.
• STEP 10

  • PEP releases its phosphate molecules and are picked up by ADP to form ATP
  • catalyzed by pyruvate kinase and results in the formation of pyruvate and ATP molecules.
• A total of 2 ATP molecules are produced from one molecule of G3P
• Aside from ATP, NADH is also produced. When G3P is oxidized to form BPG, a hydrogen atom is released from it and is picked up by NAD+ to form NADH.
• there are 4 ATP and 2 NADH molecules produced during the energy-harvesting phase of glycolysis
• Pyruvate

  • essential to the whole process of cellular respiration because it will help initiate the Krebs cycle
  • before entering the Krebs cycle, pyruvate undergoes oxidation to form an acetyl group during the transition reaction.
  • Then, the acetyl group reacts with coenzyme A forming acetyl-CoA
• It is the acetyl-CoA that enters the Krebs cycle and reacts with oxaloacetate

  (reactant of the Krebs cycle).