end of Glycolysis and start 16of 16 Mechanisms

Overview of Glycolysis

Introduction

  • Discussion of the need for understanding the structures and functions involved in glycolysis.
  • Importance of knowing:
    • Structures involved in glycolysis
    • Enzymes responsible for specific reactions
    • Order of enzymatic activities
    • Names and structures of intermediates

Isomerization of Fructose

  • Isomerization from glucose to fructose is crucial.
  • Drawing of fructose structure, highlighting different carbon atoms.
    • Definition of terms:
    • Alpha carbons: Carbons adjacent to the carbonyl group.
  • Discussion of deprotonation and stabilization through resonance.
    • Key Point: Alpha carbon's ability to stabilize a carbanion upon deprotonation increases reactivity.

pKa Values

  • Regular hydrocarbon hydrogen has a pKa of around 30.
    • Meaning: Extremely few hydrogens will deprotonate without strong conditions.
  • Alpha carbon near a carbonyl has a pKa of around 19.
    • Importance: Enhanced reactivity with up to 1 in 10,000 deprotonating under 1 M NaOH compared to 1 in a trillion for regular hydrocarbons.
    • Influence of a carbonyl group on reactions is significant in the glycolysis pathway.

Enzyme Activity in Glycolysis

  • Glucose’s reactive alpha carbon:
    • Only one active carbon in glucose.
  • In fructose, moving the carbonyl group allows more middle-carbons to become active.
    • Implication: Increased reactivity broadens the range for further biochemical reactions.

Glycolytic Steps and Enzyme Functions

  • Hexokinase: Phosphorylates glucose to glucose-6-phosphate (G6P).
    • Needs ATP for phosphorylation.
  • Phosphofructokinase (PFK):
    • Enzyme that phosphorylates fructose-6-phosphate, creating fructose-1,6-bisphosphate.
    • Rates of ATP production influence regulation and inhibition mechanisms:
    • High ATP concentration can inhibit PFK through allosteric regulation and non-competitive inhibition.
  • Naming conventions:
    • Bisphosphate vs. biphosphate:
    • Bisphosphate indicates phosphates on different carbons; biphosphate suggests two phosphates attached together.
    • Example: Fructose-1,6-bisphosphate, naming as such per the positions of the phosphates.

Enzyme Roles in Catalytic Phases

  • Aldolase:
    • Cuts fructose-1,6-bisphosphate into two three-carbon sugars (glyceraldehyde-3-phosphate and dihydroxyacetone phosphate).
    • Reaction involves water and breaking a sugar bond to produce smaller sugars.
  • Importance of triose phosphate isomerase
    • Converts dihydroxyacetone phosphate into glyceraldehyde-3-phosphate for glycolysis progression.

Energy Generation and ATP Production

  • Glycolysis begins yielding energy in the form of ATP and NADH at specific steps.
    • Glyceraldehyde-3-phosphate dehydrogenase performs oxidation/reduction reactions and phosphorylates to form high-energy compound.
  • Conversion of glyceraldehyde-3-phosphate results in production of one,3-bisphosphoglycerate, involving thioester intermediate formation.

Important Enzymes and Reaction Mechanisms

  • Glyceraldehyde-3-phosphate dehydrogenase.
    • Catalyzes the conversion of G3P to 1,3-bisphosphoglycerate.
  • Pyruvate Kinase:
    • Final reaction, producing pyruvate from phosphoenolpyruvate (PEP) and yielding ATP.
  • Phosphoenolpyruvate (PEP) is a high-energy intermediate due to unstable phosphate group.

Summary of Glycolysis

  • Starting with one glucose, net ATP production is 2 (4 produced – 2 used).
  • Generation of NADH occurs without recycling during glycolysis and counts for cellular energy pathways.

Clinical and Biological Implications

  • Accumulation of lactic acid due to rapid energy demands leads to changes in blood pH.
  • Understanding glycolysis's mechanisms may highlight potential therapeutic avenues in metabolic syndrome and muscle fatigue.

Distinction in Metabolic Pathways

  • Gluconeogenesis: The ability to reconstruct glucose from pyruvate.
  • Fermentation Pathways:
    • Two pathways through pyruvate include alcoholic fermentation (yeast) producing ethanol or lactic acid fermentation found in muscles under anaerobic conditions.

Note on Diet and Nutrition

  • Vitamin B3 is essential for NAD+ synthesis, highlighting the interconnectedness of metabolism and nutrition.
Important Reactions and Regulations Summary
  • Overview of key enzymatic reactions in glycolysis, classification of reactions (endergonic vs. exergonic), and adjustment for cellular conditions.
  • Regulatory measures taken by enzymatic pathways in response to substrate concentrations to maximize efficiency in metabolism.
Conclusion
  • Glycolysis is a critical metabolic pathway converting glucose to pyruvate while producing ATP and reducing equivalents.
  • Its regulation allows cells to adapt to energy demands efficiently.
Important Definitions to Memorize
  • Bisphosphate, Pyruvate, Glyceraldehyde-3-phosphate, Fructose-1,6-bisphosphate, Phosphoenolpyruvate, NAD+ and NADH.