HB101 Lecture Notes - Lecture 6: Glycogen Phosphorylase, Blood Sugar, Hexokinase
HPE110-Lecture 6
Bioenergetics #2
Summary Bioenergetics #1
• ATP is the energy currency of the cell with most energy stored in the phosphate
bonds
• From least to most energy available to the cell sources are ATP, PCr, glucose/
glycogen, fats.
• Enzymes lower the activation energy and are denatured by extremes in pH and
temperature and their activity is modulated by levels of ADP and ATP
• The PCr reaction is fast because it’s simple
• Glycolysis results in net production of 2 ATP, 2 NADH and 2 molecules of pyruvate
• Lactate is produced to allow glycolysis to continue by replenishing NAD+ stores
Regulation of Glycolysis
• During sprint activity glycolysis must occur several hundred times faster than at rest
• Glycolysis is regulated by:
– Concentration of Glycogen phosphorylase, hexokinase (HK),
phosphofructokinase (PFK) and pyruvate kinase
– Levels of Fructose 1,6 diphosphate
– Levels of O2
Glycogen Phosphorylase
• Glycogen glucose
• Activated by:
– ↑ ADP, Ca2+, Epinephrine
• Inhibited by:
– ↑ ATP
– ↑ Fatty acids
Hexokinase
• Blood glucose glucose-6-phosphate
• Has a high affinity for Glucose
• Inhibited by:
– its product, glucose-6-phosphate.
• Important because ATP is used in this step
• Prefer to use glycogen to produce glucose-6-phosphate
– This inhibits HK and ‘spares’ blood glucose and ATP
– ↑Fatty acid
Phosphofructokinase (PFK)
• Fructose-6-phosphate fructose 1,6 bisphosphate
• Key rate limiting step
• Activated by
– ↑Fructose-6-phosphate, ADP, ↓CP
• Inhibited by:
– ↑ H+, Citrate (Krebs cycle), ATP
– Fatty acids
Pyruvate Kinase
• Final glycolytic step
• Activated by:
– ↑ Fructose-6-phosphate
• Inhibited by
– ATP
– Alanine
Lactate system and performance
• Supplements ATP-PC system when O2 supply rate is inadequate for the energy
demand.
• Primarily recruited for max efforts lasting 20-50s
• In 50-200m events lactate may rise from 1mmol/kg to >25mmol/kg in muscle
Lactate system and performance
• ↓pH inhibits PFK
• Extended reliance on glycolysis for energy production results in fatigue
• Anaerobic enzyme concentrations increase with (anaerobic) training
Removal of lactate and H+ following exercise
• Following severe exercise
– Small amounts lost in sweat, urine
– ~ 20% glyconeogenesis in the liver
– 70% re-oxidised to pyruvate then enters the Krebs
• Often occurs in the non working muscles and the heart
– Light to moderate exercise (30-50% of VO2 max) during recovery improves
recovery by maintaining high blood flow and oxidative functioning of working
musculature
– Intense exercise (>AT, >70% of VO2 max) may result in further lactate
production
The Electron Transport Chain
Aerobic Energy System
• Oxidative energy system
• Only occurs within the mitochondria
• Interaction of 2 separate pathways
1. Krebs cycle, and
2. Electron transport system
• Utilised for longer energy production 60sec+
1. Requires O2
Krebs Cycle
• Citric acid cycle or tricarboxylic acid cycle (TCA)
• Function – Complete oxidation of CHO, fats (and sometimes protein)
– Uses NAD+ and FAD+ as hydrogen carriers
• Defn Oxidation: The removal of H+ from a compound or the addition of O to it.
• Defn Reduction: Addition of H+ or removal of O
• NAD+ and FAD+ are then ‘reduced’ to NADH and FADH2 while the ‘fuel’ is ‘oxidised’
– The H+ are the high energy molecules
– H+ is carried by the NADH and FADH2 to the ETC
