Download Metabolism Aerobic Respiration Other Ways of Generating ATP

Aerobic Respiration
Metabolism
• Principle means of synthesizing ATP in
animals
• Three stages
1. Glycolysis (cytosol)
Continued
• glucose → pyruvate
2. Krebs Cycle (mitochondria)
• formation of electron carriers and CO2
3. Oxidative Phosphorylation (mitochondria)
• electron carriers create proton gradient used to generate
ATP
How Much ATP Can Be Generated?
• 4 ATP gross (2 ATP net) in glycolysis
• 2 GTP in the Krebs cycle
• Theoretical maximum P/O ratios (#ATP per
molecule of O2 consumed) of 3 ATP per
NADH and 2 ATP per FADH2
– 10 NADH × 3 = 30 ATP
– 2 FADH2 × 2 = 4 ATP
• Maximum yield = 38 ATP per glucose
Other Ways of Generating ATP
• Anaerobic Fermentation
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Glycolysis used to generate ATP
NAD+ reduced to NADH
Must oxidize NADH back to NAD+
Reduce pyruvate into lactate
Aquatic invertebrates
• more complex pathways
• Involve Krebs cycle reactions and
truncated electron transport activity
How Much ATP is REALLY
Generated?
• Less than 38 ATP (~30 in
humans)
• Most cells transfer electrons from
cytosolic NADH to FADH2 in
the mitochondrial matrix
– Lose 2 ATP
• Proton leakage across inner
mitochondrial membrane
– Lower actual P/O ratios: ~2.5 for
NADH and 1.5 for FADH2
Anaerobic Metabolism
• Problems
– Low energy yield
– Acid production affects cell/body pH
• What do you do with it?
– Reuse it
• Lactate used by liver to regenerate glycogen (Cori cycle)
– Get rid of it
• Carp convert lactate to ethanol and release it through gills
• Aquatic invertebrates release various organic molecules
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Other Ways of Generating ATP
• Phosphagen Usage
– Molecules store high energy
phosphate groups
• Arginine phosphate (invertebrates)
• Creatine phosphate (vertebrates)
– Transfer PO4 groups to ADP as
ATP/ADP ratio lowers
– Take up PO4 groups from ATP as
ATP/ADP ratio increases
Metabolism in Low O2
• Metabolism is independent
of O2 concentrations to some
degree (O2 regulation)
• Low O2 may affect
metabolism (O2 conformity)
Metabolism and Locomotion
• Types of Locomotion
– Cursorial
– Swimming
– Flight
• How do these compare in
energetic efficiency?
Other Ways of Generating ATP
• Stored Oxygen
– Gas-binding pigments in
tissues (e.g., myoglobin) can
provide a reservoir of oxygen
for aerobic respiration
– Release O2 if intracellular PO2
drops
Responses to Low O2
• Increase ability to uptake O2
• Increased tolerance of
hypoxia
– Reliance on anaerobic
metabolism
Factors Influencing Cost of
Locomotion
• Support for body weight provided by the
media
– e.g. water – high support of body weight
– e.g. air – low support for body weight
• Resistance to movement
– Dependent on density and viscosity of media
– e.g. water – high resistance
– e.g. air – lower resistance
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Cursorial Movement
• Use limbs as levels to push against
solid substrate
• More energy required to run at higher
velocities
Cursorial Movement
• Different patterns of limb movement (gaits)
most efficient at different speeds
• With increased speed, gait transitions occur
– E.g. humans: walk → run
– E.g. horses: walk → trot → gallop
– Generally linear increase
– Curvilinear at high speeds
Energetic Cost of Transport
• COT = O2 consumed/distance traveled
– Certain gaits are most efficient at a set
speed
– E.g. horses: run at speeds in each gait that
minimize cost of transport
Flight
• U-shaped relationship between O2
consumption and flight speed
– O2 consumption minimized at a certain flight
velocity
– ↑O2 consumption at higher AND lower speeds
• Wing beats generate thrust and lift
– Bernoulli effect
– ↑ speed, ↑ lift
– At low speeds, more lift has to be generated by
downward beating of wings
Cost of Transport and Body Size
• Small animals tend to have
greater increases in energy
expenditure with increasing
velocity
• Energetic cost of transport
higher for smaller animals
• Similar relationship among
diverse animal taxa
Cost of Flight
• Speed of lowest cost of transport ≠
speed of minimum VO2
• e.g. parakeets
– min VO2 at 35 kph
– Min COT (VO2*kg-1*km-1) at 40 kph
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Swimming
• Dense, viscous medium
• Supports body mass
• Generates high levels of drag
– Force exerted in opposite direction of movement
• Affected by media density, shape, size and velocity
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↑ w/ density and viscosity
↓ with streamlining
Drag α surface area
Drag α velocity2
Which is the Most Efficient?
• Swimming has the least expensive COT
– Low speed, but no need for body support
• Flight has the next least expensive COT
– High energy input required, but high speeds
and low drag increase efficiency
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