Download Chapter 3: Bioenergetics

Chapter 3:
Bioenergetics
Introduction
• Metabolism: total of all chemical reactions
that occur in the body
– Anabolic reactions
• Synthesis of molecules
– Catabolic reactions
• Breakdown of molecules
• Bioenergetics
– Converting foodstuffs (fats, proteins,
carbohydrates) into energy
Objectives
• Discuss the function of cell membrane,
nucleus, & mitochondria
• Define: endergonic, exergonic, coupled
reactions & bioenergetics
• Describe how enzymes work
• Discuss nutrients used for energy
• Identify high-energy phosphates
1
Objectives
• Discuss anaerobic & aerobic production of
ATP
• Describe how metabolic pathways are
regulated
• Discuss the interaction of anaerobic &
aerobic ATP production during exercise
• Identify the rate limiting enzymes
Cell Structure
• Cell membrane
– Protective barrier between interior of cell and
extracellular fluid
• Nucleus
– Contains genes that regulate protein
synthesis
• Cytoplasm
– Fluid portion of cell
– Contains organelles (mitochondria)
Structure of a Typical Cell
Fig 3.1
2
Cellular Chemical Reactions
• Endergonic reactions
– Require energy to be added
• Exergonic reactions
– Release energy
• Coupled reactions
– Liberation of energy in an exergonic reaction
drives an endergonic reaction
The Breakdown of Glucose:
An Exergonic Reaction
Fig 3.3
Coupled Reactions
Fig 3.4
3
Oxidation-Reduction Reactions
• Oxidation: removing an electron
• Reduction: addition of an electron
• Oxidation and reduction are always
coupled reactions
• In cells often involve the transfer of
hydrogen atoms rather than free electrons
– Hydrogen atom contains one electron
– A molecule that loses a hydrogen also loses
an electron, and therefore is oxidized
Enzymes
• Catalysts that regulate the speed of
reactions
– Lower the energy of activation
• Factors that regulate enzyme activity
– Temperature
– pH
• Interact with specific substrates
– Lock and key model
Enzymes Lower the
Energy of Activation
Fig 3.6
4
EnzymeSubstrate
Interaction
Fig 3.7
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Fuels for Exercise
• Carbohydrates
– Glucose
• Stored as glycogen
• Fats
– Primarily fatty acids
• Stored as triglycerides
• Proteins
– Not a primary energy source during exercise
High-Energy Phosphates
• Adenosine triphosphate (ATP)
– Consists of adenine, ribose, and three linked
phosphates
• Formation
ADP + Pi → ATP
• Breakdown
ATP
ATPase
ADP + Pi + Energy
5
Structure of ATP
Fig 3.8
Model of ATP as the Universal
Energy Donor
Fig 3.9
Bioenergetics
• Formation of ATP
– Phosphocreatine (PC) breakdown
– Degradation of glucose and glycogen (glycolysis)
– Oxidative formation of ATP
• Anaerobic pathways
– Do not involve O2
– PC breakdown and glycolysis
• Aerobic pathways
– Require O2
– Oxidative phosphorylation
6
Anaerobic ATP Production
• ATP-PC system
– Immediate source of ATP
PC + ADP
Creatine kinase
ATP + C
• 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
Glycolysis
Energy Investment Phase
Fig 3.11
7
Glycolysis
Energy Generation Phase
Fig 3.11
Oxidation-Reduction Reactions
• Oxidation
– Molecule accepts electrons (along with H+)
• Reduction
– Molecule donates electrons
• Nicotinomide adenine dinucleotide (NAD)
NAD + 2H+ → NADH + H+
• Flavin adenine dinucleotide (FAD)
FAD + 2H+ → FADH2
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
8
Conversion of Pyruvic Acid
to Lactic Acid
Fig 3.12
Aerobic ATP Production
• Krebs cycle (citric acid cycle)
– Completes the oxidation of substrates and
produces NADH and FADH to enter the
electron transport chain
• Electron transport chain
– Oxidative phosphorylation
– Electrons removed from NADH and FADH
are passed along a series of carriers to
produce ATP
– H+ from NADH and FADH are accepted by
O2 to form water
The Three
Stages of
Oxidative
Phosphorylation
Fig 3.13
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The Krebs Cycle
Fig 3.14
Relationship Between the
Metabolism of Proteins, Fats, and
Carbohydrates
Fig 3.15
Electron Transport Chain
Fig 3.17
10
The Chemiosmotic Hypothesis
of ATP Formation
• Electron transport chain results in pumping
of H+ ions across inner mitochondrial
membrane
– Results in H+ gradient across membrane
• Energy released to form ATP as H+ diffuse
back across the membrane
The Chemiosmotic Hypothesis
of ATP Formation
Fig 3.16
Aerobic ATP Tally
Metabolic Process
High-Energy
Products
ATP from Oxidative ATP Subtotal
Phosphorylation
Glycolysis
2 ATP
2 NADH
—
5
2 (if anaerobic)
7 (if aerobic)
Pyruvic acid to acetyl-CoA 2 NADH
5
12
Krebs cycle
—
15
3
14
29
32
2 GTP
6 NADH
2 FADH
Grand Total
32
2.5 ATP per NADH
1.5 APT per FADH
Table 3.1
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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
Control of Bioenergetics
• Rate-limiting enzymes
– An enzyme that regulates the rate of a
metabolic pathway
• Levels 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
• Calcium may stimulate aerobic ATP
production
Action of Rate-Limiting
Enzymes
Fig 3.19
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Control of Metabolic Pathways
Pathway
Rate-Limiting
Enzyme
Stimulators
Inhibitors
ATP-PC system
Creatine kinase
ADP
ATP
Glycolysis
Phosphofructokinase AMP, ADP, Pi, ↑pH ATP, CP, citrate, ↓pH
Krebs cycle
Isocitrate
dehydrogenase
++
ADP, Ca , NAD
ATP, NADH
ATP
Electron transport Cytochrome Oxidase ADP, Pi
chain
Table 3.2
Control of Bioenergetics
Glycogen
ATP-PC System
PC + ADP
C + ATP
Glucose
1
Rate Limiting Enzymes
1. Creatine kinase
2. Phosphofructokinase
3. Iscitrate dehydrogenase
4. Cytochrome oxidase
Glucose 6-phosphate
Glycerol
Triglycerides
2
Phosphoglyceraldehyde
Glycolysis
Pyruvic Acid
Lactic Acid
β-ox
Acetyl CoA
Fatty acids
Ketone
bodies
Table 3.2
C4
Kerb’s
Cycle
3
Amino Acids
C6
C5
Proteins
Urea
NADH
FADH
ETS
4
Interaction Between Aerobic
and Anaerobic ATP Production
• Energy to perform exercise comes from an
interaction between aerobic and anaerobic
pathways
• Effect 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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