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 UseDuring 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 fatty-acids 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 - production at onset

ATP rate - production

Return to normal

Aerobic catabolism using pre-existing 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 (brine-shrimp 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?