Energy Systems 2 Flashcards
(82 cards)
What is a characteristic of ATP supply from substrate-level phosphorylation?
Rapid but capacity-limited
Why is the CK reaction, despite being rapid, capacity-limited?
Phosphorylcreatine stores are small, and its breakdown produces elevated Pi
Why does glycolysis have a large capacity in theory?
limited only by glycogen availability
What limits the theoretical large capacity of glycolysis for ATP supply?
Protons associated with lactate production reduce cell pH and inhibit PFK
What is the only sustainable ATP supply that can support exercise lasting days?
Oxidative phosphorylation`
What three conditions are required for oxidative phosphorylation to proceed?
- Sufficient ‘signal’ to activate it (ADP)
- Enough substrate (CHO and fat),
- Enough oxygen to accept products (protons and electrons)
What is a major problem with oxygen in aerobic metabolism?
It is stored in small amounts in the cell and mostly transported from the atmosphere
Why can’t macronutrient substrates (fat and carbs) be directly broken down by the TCA cycle?
They need to be converted to acetyl CoA first
What is a problem with the location of oxidative phosphorylation in relation to ATP use?
It takes place in mitochondria, far from sites of ATP use, so the ‘signal’ (changes in ATP, ADP, and Pi) appears far from where it needs to be seen
What is the substrate delivery issue in oxidative phosphorylation?
Oxygen must travel from air to mitochondria to support ATP production
What energy systems help before oxygen supply meets demand?
PCr hydrolysis and glycolysis
What did A V Hill’s experiment show?
Oxygen uptake lags behind energy demand at exercise onset
What does the oxygen uptake curve show during the rest-to-exercise transition?
Aerobic ATP supply increases gradually and reaches a steady state after 2 to 3 minutes where oxidative phosphorylation meets the ATP demand of submaximal exercise
What is the oxygen deficit + why was this astonishing to be labelled / identified?
Gap between energy demand and aerobic supply at onset
- Hill identified we have energy coming from glycolysis but didn’t take into account PC as it hadn’t been discovered - so was quite astonishing he knew O2 deficit was in any way anaerobic
What did Rossiter et al (1999) show about the relationship between VO₂ and PCr during exercise onset?
VO₂ uptake increases at the same rate that PCr decreases showing that oxidative phosphorylation is being activated in response to PCr breakdown
Why is there a delay in VO₂ uptake compared to PCr breakdown?
Delay reflects time for blood and signals to travel from muscle to lungs and for respiratory and cardiovascular systems to respond
What happens when the rate of PCr hydrolysis is matched by oxidative ATP synthesis?
A steady state is reached where ATP demand is met almost entirely by aerobic ATP supply and PCr stops falling
What is the role of creatine kinase (CK) in both cytoplasm and mitochondria?
In cytoplasm CK breaks down PCr to resynthesise ATP from ADP while mitochondrial CK uses ATP from oxidative phosphorylation to resynthesise PCr from Cr and Pi
How does the PCr shuttle signal mitochondria to increase oxygen uptake?
Breakdown of PCr increases Cr and Pi in cytoplasm which signals mitochondria to stimulate oxidative phosphorylation
What are the four steps of the PCr shuttle during rest-to-exercise transition?
- PCr breakdown begins immediately
- Cr and Pi increase in cytoplasm and enter mitochondria
- Mitochondria increase oxygen uptake slowing PCr fall
- Eventually aerobic ATP production matches PCr use reaching steady state
What does the coupling of VO₂ uptake and PCr breakdown show about energy systems?
That all energy systems are interlinked and function as one integrated system
What are the two essential roles of PCr in muscle cells?
- Defends ATP concentration via the Lohmann reaction
- Acts as a capacitor for aerobic metabolism by buffering spatial and temporal energy supply
What is meant by PCr acting as a spatial buffer?
Spatial buffer prevents ATP and ADP diffusing from sites of supply and use via CK distribution
What is meant by PCr acting as a temporal buffer?
Temporal buffer slows required rate of oxygen delivery by allowing PCr to fall and delay oxygen uptake demands
