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Chapter 14.1 and 14.2: Glycolysis and Feeder
Pathways
CHEM 7784
Biochemistry
Professor Bensley
CHAPTER 14.1 and 14.2 Glycolysis
– Process of harnessing energy from glucose via glycolysis
– Various pathways by which carbohydrates other than glucose enter glycolysis
Today’s Objectives: To learn and understand the
Central Importance of Glucose
• Glucose is an excellent fuel
• Glucose is a versatile biochemical precursor
• Four major pathways of glucose utilization
Glycolysis: The Big Picture
•Anaerobic process carried out by all cells but at different rates
•Converts hexose to two pyruvates
•Generates 2 ATP and 2 NADH
•For certain cells in the brain and eye, glycolysis is the only ATP generating pathway
Glucose + 2 ADP + 2 NAD+ + 2Pi
2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2H20
Glycolysis: Importance
• Glycolysis is a sequence of ten enzyme-catalyzed reactions by which glucose is converted into pyruvate
• Two phases: – First phase converts glucose to two G-3-P – Second phase produces two pyruvate
molecules
• Three possible fates for pyruvate
Glycolysis: The Preparatory Phase
Glycolysis: The Payoff Phase
STEP 1 - The Hexokinase Reaction
• The first step, phosphorylation of glucose, is catalyzed by hexokinase in eukaryotes, and by glucokinase in prokaryotes
• This process uses the energy of ATP
STEP 2 - Phosphohexose Isomerization
• An aldose can isomerize into ketose via an enediol intermediate
• Overall – Glucose-6-Phosphate is converted to Fructose-6-Phosphate
STEP 3 - The Second Priming Reaction; The First Commitment
• This is an irreversible step• The product, fructose 1,6-bisphosphate is
committed to become pyruvate and yield energy
STEP 4 - Aldolases Cleave 6-Carbon Sugars
• Step four is the cleavage of Fructose 1,6-Bisphosphate
STEP 5 - Triose Phosphate Interconversion
• DAP is converted enzymatically to GAP
STEP 6 - Glyceraldehyde 3-Phosphate Dehydrogenase Reaction
• First step in the “Payoff Phase” of Glycolysis• First energy-yielding step in glycolysis
STEP 7 - First Substrate-Level Phosphorylation
• 1,3-bisphosphoglycerate is a high-energy compound that can donate the phosphate group to ADP to make ATP
STEP 8 - Conversion of 3-Phosphoglycerate to 2-Phosphoglycerate
• This is a reversible isomerization reaction
Mechanism of the Phosphoglycerate Mutase Reaction
STEP 9 - Dehydration of 2-Phosphoglycerate
• The goal here is to create a better phosphoryl donor• Loss of phosphate from 2-phosphoglycerate would merely
give a secondary alcohol with no further stabilization …
STEP 10 - Second Substrate-Level Phosphorylation
… but loss of phosphate from phosphoenolpyruvate yields an enol that tautomerizes into ketone
Feeder Pathways for Glycolysis