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Chapter 3,Part 2

Bioenergetics

Anaerobic ATP Production

1. ATP-PC system– Immediate source of ATP

PC + ADP ATP + CCreatine kinase

100%

% C

apacity of Energy System

10 sec 30 sec 2 min 5 min +

Energy Transfer Systems and Exercise

Aerobic Energy System

Anaerobic Glycolysis

ATP - CP

Anaerobic ATP Production

2. Anaerobic Glycolysis– Produces ATP through a biochemical process– Food source is glycogen or glucose

Glycogenolysis-breakdown of glycogen stored in muscle (glycogen is also stored in liver)Glycolysis-breakdown of glucose

Anaerobic ATP Production

Glycolysis– Energy investment phase

Requires 2 ATP– Energy generation phase

Produces ATP, NADH (carrier molecule), and pyruvate or lactate

The Two Phases of Glycolysis

Fig 3.10

2

Glycolysis

Glucose – C6H12O6

Pyruvic Acid - C3H4O3

Glycolysis– C6H12O6 ⎯→ 2 C3H4O3 + 2 H+ + energy (2

ATP)W/ O2

– NAD + 2 H+ → NADH + H+ (Krebs cycle)

Production of Lactic Acid

Normally, O2 is available in the mitochondria to accept H+ (and electrons) from NADH produced in glycolysis– In anaerobic pathways, O2 is not available

H+ and electrons from NADH are accepted by pyruvic acid to form lactic acid

Anaerobic Glycolysis

Lactic Acid – C3H6O3

– C6H12O6 ⎯→ 2 C3H6O3 + energy (2 ATP)W/O O2

Conversion of Pyruvic Acid to Lactic Acid

Fig 3.12

Anaerobic Glycolysis

Characteristics– Begins about 20 sec into high intensity

exercise and continues for about 3 minutes– Uses only glucose or glycogen– Enzymes located in the cytoplasm– 12 biochemical steps producing 2 to 3 ATP– Intensity less than 100% (70-90% max)

Anaerobic Glycolysis

Characteristics (cont) – Does not require oxygen– Limited at about 3 min by the buildup of lactic

acid which decreases the pH– Acidic environment halts enzyme activity

Phosphofructokinase (PFK)– Glucose – 2 ATP– Glycogen – 3 ATP

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The Two Phases of Glycolysis

Fig 3.10

Glycolysis Energy Investment Phase

Fig 3.11

Glycolysis Energy Generation Phase

Fig 3.11

100%

% C

apacity of Energy System

10 sec 30 sec 2 min 5 min +

Energy Transfer Systems and Exercise

Aerobic Energy System

Anaerobic Glycolysis

ATP - CP

Aerobic ATP Production

3. Krebs cycle (citric acid cycle, TCA cycle)– Completes oxidation of H+

– Removed from CHO, fats, Proteins– NAD, FAD – H+ carriers– H+ contains potential energy from food

molecules

Aerobic ATP Production

H+ transported to electron transport chain– Combines ADP + P → ATP

Oxygen availability– Final hydrogen acceptor – Forms H2O

3 steps– Breakdown of foodstuffs– Oxidative phosphorylation – Electron transport chain

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The Three Stages of Oxidative

Phosphorylation

Fig 3.13

The Krebs Cycle

Fig 3.14

Relationship Between the Metabolism of Proteins, Fats, and

Carbohydrates

Fig 3.15

Electron Transport Chain

Fig 3.17

Aerobic Glycolysis

Electron Transport System (chain)

H+ + e- + O2 → H2OADP + Pi → ATP

Beta Oxidation

Breakdown of lipids1 ATP required for fats to be activated for– ß oxidation process

Fats enter at Krebs cycle and pass to ETCFats produce much higher amounts of ATP per mol. than glycogen

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Beta Oxidation

2 C fat compound – Stearic acid is an 18 C fat

yields 147 ATP– Palmitic acid is a 16 C fat

130 ATP

Fats require 15% more oxygen per ATP produced than CHO requireFats cannot be metabolized anaerobically

Aerobic

Characteristics– Requires presence of oxygen (aerobic)– Can use glucose, glycogen, fatty acids, and/or

amino acids for fuel– Provides 85% of the energy required by body

15% glycolysis– Produces ATP during rest and low level

exercise

Aerobic

Characteristics (cont)– Oxidative phosphorylation occurs in

mitochondria– Makes relatively large amounts of ATP– Glycogen = 33 ATP– Glucose = 32 ATP

Aerobic

GlycogenolysisGlycogen → 3 ATP + 2 Pyruvic Acid– (C6H12O6)n → 3 ATP + 2 C3H4O3

GlycolysisGlucose → 2 ATP + 2 Pyruvic Acid– C6H12O6 → 2 ATP + 2 C3H4O3

Aerobic

2 Pyruvates → 2 Acetyl CoA (CO2) Krebs cycle (TCA cycle)

2 Acetyl CoA → 6 CO2 + 6 H2O + 33 (or 32) ATP

Mitochondria

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Mitochondria

Outer membrane permeable to most ionsInner membrane impermeable to most ions unless they have a specific carrierBulges of the inner membrane – cristaeDensity of cristae higher in tissues with high rate of oxidation– heart

Efficiency of Oxidative Phosphorylation

Aerobic metabolism of one molecule of glucose– Yields 32 ATP

Aerobic metabolism of one molecule of glycogen– Yields 33 ATP

Overall efficiency of aerobic respiration is 34%– 66% of energy released as heat

Aerobic system

Summary EquationC6H12O6 + 6 O2 + 32 ADP + 32 Pi →– 6 CO2 + 6 H2O + 32 ATP

(C6H12O6)n + 6 O2 + 33 ADP + 33 Pi →– 6 CO2 + 6 H2O + 33 ATP

Control of Bioenergetics

Rate-limiting enzymes– An enzyme that regulates the rate of a

metabolic pathwayLevels of ATP and ADP+Pi– High levels of ATP inhibit ATP production– Low levels of ATP and high levels of ADP+Pi

stimulate ATP production

Control of Metabolic Pathways

Pathway Rate-limiting Stim InhATP/PC creatine kin ADP ATPGlycolysis PFK AMP ATP

ADP CP ↑ pH Pi ↓

Krebs Isocitr dehy ADP ATPETC cyto oxidase ADP ATP

Table 3.2

Interaction Between Aerobic and Anaerobic ATP ProductionEnergy to perform exercise comes from an interaction between aerobic and anaerobic pathwaysEffect of duration and intensity– Short-term, high-intensity activities

Greater contribution of anaerobic energy systems– Long-term, low to moderate-intensity exercise

Majority of ATP produced from aerobic sources

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Exercise Time and Lactate Production

100%

% C

apacity of Energy System

10 sec 30 sec 2 m in 5 m in +

Energy Transfer System s and Exercise

Aerobic Energy System

Anaerobic G lycolysis

ATP - CP

Regulation of Metabolism

Low Intensity– < 40-50% VO2max

Medium Intensity– 50-70% VO2max

High Intensity– 70-120% VO2max

Energy Systems during Exercise

Submaximal– 2/3 fat– 1/3 CHO (glucose/glycogen)– Steady state-oxygen consumption meets

oxygen demand to provide ATP– Adjustment time needed to reach steady state– 30 min or more

Energy Systems during Exercise

Submaximal (cont)– Major fuel is fat– ATP-PC and LA contribute during the first 2-3

min of exercise– BLa is not high so anaerobic glycolysis and

LA are not primary contributor– BLa of marathoners is only about 20-30 mg%

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Energy Systems during Exercise

Submaximal (cont) – forever?Fatigue factors

low blood glucose (liver glycogen depletion)low muscle glycogen-muscular fatiguedehydration and electrolyte loss (core temp)boredom, physical beating

Energy Systems during Exercise

Maximal exercise – 1/4 fat– 3/4 CHO (glucose/glycogen)

Anaerobic sources

Summary

The key determining factor in which energy system predominates:– Exercise intensity