Cellular Energetics Flashcards
• Breathing air (oxygen) from birth to death is ONLY so that
biological
oxidations can take place in the cells
• The mitochondria use oxygen to
generate energy (ATP) – this is called ‘oxidative phosphorylation’
• Fuels such as glucose and fatty acids are used to
generate energy in
the form of ATP (from ADP & Pi
)
• The energy in ATP is available for:
i) moving ions across membranes against their conc. or electrical
gradient
ii) muscle contraction
iii) nerve conduction etc.
How is fuel ENERGY Quantified?
The BOMB Calorimeter
The BOMB Calorimeter
Food is ignited • ∆Temp of H2O is measured • Thermal capacity of H2O is known • Mass of sample is known • Therefore, the oxidative energy content can be calculated
The _____ ______ content of a food sample is the same whether
liberated by uncontrolled combustion in a bomb calorimeter or by
controlled enzymatic decomposition within the cells of living organisms.
oxidative energy
BOMB Calorimeter will tend to over estimate energy available
Cellulose ,Fibre = food material that can’t be digested ( humans dont have enzymes to break down)
Oxidising different fuels yields similar amounts
of energy per unit O2 consumed
Glucose, Fat, Protein Energy released (kJ g-1) = 16,39, 18
Glucose metabolism eqn
𝐂6𝐇12𝐎𝟔 + 𝟔O2 + 32ADP + 32Pi → 6CO2 + 6H2O + 𝟑2ATP
The main waste products of mitochondrial oxidation of substrates are
CO2 and NH3 (ammonia)
CO2 and NH3 (ammonia)
Both are water soluble & carried in the blood
– CO2 excreted by ?
– NH3 carried to liver where?
diffusion into the lung & by the kidney as HCO3-
it is eventually converted to urea & excreted by the kidneys.
α-ketoglutarate (TCA cycle) is important for _____ __________. Reaction with ___means that it is not available
for oxidative phosphorylation and this can be toxic, especially to the brain.
oxidative phosphorylation
NH3
NH3 + α ketoglutarate → glutamate + H2O
VO2max
• the maximal rate of consumption of oxygen
• a measure of ‘aerobic capacity’
• units are L/min
(or L min-1)
VO2 max is reached when
oxygen consumption remains at a
steady state despite an increase in workload
Fick principle used to measure VO2
- Subject breathes using a respiratory valve
- Inspired gas content known
- Expired air analysed for O2 & CO2 content
- Volume expired measured
Energy Efficiency
Mechanical Output: Work rate (Power), Speed, Distance, Time (heat)
over
• Metabolic Input: Fuel usage, O2 uptake, ATP turnover
Efficiency eqns
=
output/input
=
power/VO2
Energy can be used by the cell for:
- Chemical work: moving a molecule against its concentration
gradient - Electrical work: moving a molecule against its electrical gradient
- Mechanical work: e.g muscle contraction
The Sarcolemmal Na+/K+-ATPase
a membrane-bound electrogenic enzyme that moves Na+ out of
the cell (efflux) and K+ into the cell (influx) against their
concentration gradients and electrical gradient (Na+)
3Na+ out & 2K+ in
Electro-chemical Work
The TOTAL work done (i.e. energy performed) in
moving an ion across the sarcolemma is merely the
sum of the chemical and electrical components:
The PRINCIPLE Energy Sinks of exercising skeletal /
cardiac muscle are:
- The sarcolemmal Na+/K+ ATPase
- The sarcoplasmic reticular Ca2+ -ATPase
- The cross-bridge actomyosin-ATPase
These Energy Sinks perform Work:
- Chemical
- Electrical
- Mechanical
Main energy ‘sink’ in active muscle cells
Stoichiometry is 1 ATP: 1 crossbridge
Myosin ATPase
The WORK performed in pumping Ca2+ ions from cytoplasm back into sarcoplasmic
reticulum (SR):
The Sarcoplasmic Reticular
Ca2+-ATPase (SERCA)
1ATP for 2 Ca++
The ‘Cost’ of a Contraction Trigger
Ca2+ ions are released from the sarcoplasmic reticulum (SR) and
bind to the myofilaments to trigger contraction.
Ca2+ is then taken back up into the SR by the SRCa2+-ATPase pump.
