Aerobic and Anaerobic Forms of
Metabolism
Exercise and energy
• Energy is needed for all exercises
• ATP, the most important molecule carrying
energy, can be stored in• small amount but is not
exchange à need to be made on a constant
Mechanisms of ATP production
• 4 major sets of
reactions in aerobic
catalysis:
– Glycolysis
– Krebs cycle
– Electron transport chain
(ETC)
– Oxidative
phosphorylation
• All 3 major categories
of food can be
degraded through
these processes
Electron transport chain
Net results from glycolysis and Krebs cycle
•Glycolysis:
1 glucose + 2 ADP + 2 NAD + 2 P à
2 pyruvic acid + 2 ATP + 2 NADH+ + 2 H2O
•Krebs cycle
2 pyruvic acid + 6 NAD + 2 FAD à
8 NADH+ + 2 FADH + 2 GTP + 6 CO2
Electron Transport Chain (ETC)
NADH+ + ADP + ½ O2 à NAD + 3 ATP + H2O
FADH + ADP + ½ O2 à FAD + 2 ATP + H20
Oxidative phosphorylation
ADP + Pi à ATP
• P/O ratio = expresses the yield of ATP formation by oxidative
phosphorylation (OP) per atom of O2 reduced to H2O
• If complete coupling between ETC and OP: 3 ATP formed
• If completely uncoupled: 0 ATP
• During uncoupling, NAD and FAD are formed but instead of
ATPs formed, heat is produced à used by mammals to
produce heat during cold seasons and a mean to control
weight.
• Max of 34 ATPs from OP
• Additional ATPs from substrate phosphorylation
• Total ATPs = 40-2 = 38
Consequences of O2 deficiency
• Lack of O2 à ETC becomes
fully reduced and is blocked à
no ATP, no NAD and FAD
regenerations
• Some tissues can generate
some ATP without O2 à
anaerobic glycolysis
• Formation of lactic acid and
regeneration of NAD
• Muscles can do that, not brain
• Net production of 2 ATP /
glucose
• Mammalian brains use
ATP much faster than
can be produced
anaerobically à these
brains must have O2!
• If no ATP à Na+ K+
pump, Ca++ pump do
not function à neurons
destroyed
Fates of catabolic end-products
• Aerobic glycolysis:
• Glucose is fully degraded à
CO2 + H2O production à
respiration
• Anaerobic end-products: lactic
acid:
– molecule still rich in energyà
wasteful to eliminate
– But too toxic to retain in large
amount
– Anaerobic conditions are usually
short à possibility to use lactic
acid later
• Vertebrates can
metabolize lactic acid
–Gluconeogenesis
(6 ATP + O2 used)
–Or full oxidation to CO2 +
H2O and 36 ATP
formation
Steady / Non-steady state
• Steady-state mechanism of ATP production if:
– 1. ATP produced as fast as it is used
– 2. uses raw materials no faster than it is replenished
– 3. chemical by-products voided as fast as produced
– 4. cell remains in homeostatic equilibrium
• Non-steady state:
– ATP is consumed faster than it is produced
– Wastes are accumulating faster than they can be
eliminated
– Ex: phosphagen system
Patterns of Energy Use
–Sustained or short burst
–Mild or Strenuous
Patterns of Energy Use
During sustained exercise:
- ATP is consumed
- when the ATP stores are down, use of the
phosphagen compounds
- creatinine phosphate found in
vertebrate muscle,
- arginine phosphate in invertebrates
Then, ATP is aerobically synthesized from
fatty-acids and/or glucose
-Muscles are especially geared to use fattyacids à derived from fat (triglycerides through
b-oxidation in the liver)
-Glucose is used or synthesized from
glycogen reserves
• Aerobic ATP synthesis
needs….. O2!
• If the exercise is
strenuous, the O2 store
might not be adequate to
support this synthesis
• Then, the body has no
choice but to turn to
anaerobic glycolysis à less
efficient ATP synthesis +
lactic acid accumulation
Muscle fatigue and return to resting
state
• Many causes:
– Lack of O2 in the muscle
or in the blood
– Lack of glucose or
glycogen store
– Accumulation of lactic
acid
– Accumulation of calcium
ions in inappropriate cell
compartments
Mechanisms of ATP production and use
Mechanisms of
ATP production
Mode of
operation
ATP yield
ATP rate - ATP rate - Return to
production production normal
at onset
Aerobic
catabolism
using preexisting O2
Non steady
Small
Fast
High
Fast
Aerobic
catabolism
Steady
High
Slow
Moderate
------
Phosphagen
use
Non steady
Small
Fast
High
Fast
Anaerobic
glycolysis
Non steady
Moderate small
Fast
High
Slow
Muscle fiber types
• Slow oxidative (SO)
– Rich in mitochondria
– High level of enzymes
involvd in oxidative
pathways
– Muscle rich in blood
vessels and myoglobin
à red color
• Fast glycolytic (FG)
– Rich in ATPase
– Less blood vessels,
mitochondria à white
color
Uses of energy in animals ??
• Birds during migration
• Lobsters during escape
behavior (short burst of
tail muscle contraction)
• Salmons during
upstream migration
• Antelope during
escape run
Response to decreased O2 in
environment
• Shut-down
metabolism à
dormancy (brineshrimp embryo
• Diving animals: dive
long enough to use O2
store and/or use
anaerobic glycolysis à
lactic acid use à must
be eliminated prior to
next dive
• Some animals (diving
turtles) can sustain
long periods without
oxygen:
– Uses metabolic
depression to maintain
brain tissue integrity
– Turtles become
comatose, accumulate
large store of lactic acid
ATP synthesis under reduced O2
availability
• O2 regulation: steady
rate of O2
consumption and ATP
synthesis despite
changing level of O2.
possible only over a
certain range of [O2]
• O2 conformity: O2 rate
of consumption falls
with O2 in environment
Water-breathing anaerobes
• Uncommon: some clams,
mussels, worms, some
goldfishes à buried in
marsh sediments (no O2)
• Strategy to survive
anoxia:
– metabolic depression
– ATP synthesis through acetic,
succinic, proprionic acids
and alanine synthesis à
excreted in environment à
less acidity
Anaerobiosis in goldfish and crucian
carp
• These fishes
synthesize LDH à
lactic acid formation
• Muscles can convert
lactic acid to ethanol +
CO2
• Consequences?