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Chapter 3
Bioenergetics
Chapter 3
Bioenergetics
Converting foodstuffs (fats,
proteins, carbohydrates) into
energy
Metabolism

Total of all chemical reactions that occur
in the body
– Anabolic reactions
• Synthesis of molecules
– Catabolic reactions
• Breakdown of molecules
Cellular Level

Look back……
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
Even the Smallest Cells…
…are huge compared to the “bits and
pieces” and chemicals in them.
If you had to wait for random action, you’d
wait forever!
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
• “Harnessed energy to accomplish a task”

Example:
– “Combustion” of Carbohydrate
C6H12O6 reacts with 6O2 to become
6CO2 and 6H20 and Energy
C6H12O6 + 6O2
6CO2 + 6H20 + Energy
The Breakdown of Glucose:
An Exergonic Reaction
Can we regulate reactions?



Make sure the reactions occur.
Make the reactions occur in a timely
manner (speed up the reaction).
Prevent the reaction from occurring or
slow it down – Rate Limiting
Enzymes

Catalysts that regulate the speed of
reactions
– Lower the energy of activation
– Create specific conditions for reactions
Enzymes

Factors that regulate enzyme activity
– Temperature
– pH
• work in a narrow range – large gain
Enzymes

Interact with specific substrates
– Lock and key model
Enzyme-Substrate Interaction
Action of Rate-Limiting Enzymes
How is energy converted?
Energy Systems Overview
Currency System

Money
– Gold, $100’s, $50’s, $20’s, $10’s, $5’s,
$2’s, $1’s
• Dollar coin, fifty cent, quarters, dimes, nickels,
pennies.
– Exchanged but not destroyed
– Recycled?
U.S. Currency System

A dollar has potential to do work for you.

Spend some, but still has potential left

Recycle it and it’s ready to go again

Only so much in circulation
Human Energy Currency System

Adenosine Triphosphate – ATP
Structure of ATP
High-Energy Phosphates

Adenosine triphosphate (ATP)
– Consists of adenine, ribose, and three
linked phosphates

Formation
ADP + Pi  ATP

Breakdown
ATP
ATPase
ADP + Pi + Energy
Where Does ATP Come From?

Is it in our food?

Can you buy some at the store? – GNC?

Does grandma have some in the attic?
Where Does ATP Come From?

Stored in cells (muscle**)

Store limited amounts (heavy molecule)
– Use 50 – 100 x body weight in ATP / 24 hrs.

Make it from ADP
– Recycle “used” ATP
Bioenergetics
How to make (recycle) ATP “Phosphorylation”
- adding a phosphate
Bioenergetics

Anaerobic pathways (non-aerobic)
– Do not require or involve O2
– Called direct phosphorylation
Bioenergetics

Aerobic pathways
– Require O2 molecules
– Called oxidative phosphorylation
Anaerobic ATP Production

Stored ATP
– Immediate (1st) source of ATP
– Amount depends on muscle size
– Runs low on substrate almost immediately
- ~ 1 sec.
– Used during initiation of movement
Anaerobic ATP Production

ATP-PC system (PC= phosphocreatine)
– Stored in skeletal muscle
– Source of phosphates
– Rapid response but…
– Runs low on substrate quickly ~ 1-5 sec
PC + ADP
Creatine kinase
ATP + C
Anaerobic ATP Production

Glycolysis
– Occurs in cytoplasm
– Fairly rapid response (small lag) ~ 3+ sec
– High energy response
– High energy because of it’s speed of action
– Expensive in terms of energy required
– Lasts as long as substrates available ~ 30+ sec
– Makes product that can limit its action
Anaerobic ATP Production

Glycolysis
– Energy investment phase
• Requires 2 ATP
– Energy generation phase
• Produces 4 ATP
• Produces NADH (carrier molecule)
• Produces pyruvate or lactate
Glycolysis:
Energy Investment Phase
Glycolysis:
Energy Generation Phase
The Two Phases of Glycolysis
Glycolysis
Net ATP production =
4 ATP produced
- 2 ATP used
2 ATP available for muscle contraction
from each glucose molecule
Is That All That Happens?

No
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
Conversion of Pyruvic Acid to
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
Conversion of Pyruvic Acid to
Lactic Acid
So glycolysis is…..

1 x 6 carbon molecule split into
2 x 3 carbon molecules (costs 2 ATP)
2 x 3C molecule rearranged to make
2 x 3C pyruvic acids (makes 2 ATP each)
and 4 H+ are shuttled by 2NAD to
2 x 3C pyruvic acids to make
2 x 3C lactic acids
(if H+ s removed from lactic acid = pyruvic acid)
So glycolysis is…..



A fast method of providing energy for
movement without the need for O2
A self-limiting method
*Also a potential provider of H+ for
aerobic energy production
Aerobic ATP Production
Part 1
 Krebs cycle (citric acid cycle)
– Completes the oxidation of substrates
– Uses NAD and FAD to shuttle H+ s to the
Electron Transport System
The Krebs Cycle
So the Krebs Cycle is….

A 2C molecule added to a 4C molecule (6C)
–
–
–
–
–
rearranged to a 5C and then 4C (version)
2 x CO2 are made
3 x NADH are made
1 x FADH is made
1 x GTP (ATP) is made
Aerobic ATP Production
Part 2
 Electron Transport System “ETS”
– Oxidative Phosphorylation
Aerobic ATP Production

ETS
– Electrons removed from NADH and FADH
are passed along a series of carriers to
drive phosphorylation of ADP to ATP
– H+ from NADH and FADH are accepted by
O2 to form water – H2O (neutral)
Formation of ATP in the Electron
Transport Chain
So for each……

1 NADH through the ETS = 3 ATP made

1 FADH through the ETS = 2 ATP made
The Three Stages of Oxidative
Phosphorylation
Aerobic ATP Tally – For Glucose
Metabolic Process
High-Energy
Products
ATP from Oxidative ATP Subtotal
Phosphorylation
Glycolysis
2 ATP
2 NADH
—
6
2 (if anaerobic)
8 (if aerobic)
6
14
—
18
4
16
34
38
Pyruvic acid to acetyl-CoA 2 NADH
Krebs cycle
Grand Total
2 GTP
6 NADH
2 FADH
38
Efficiency of Oxidative
Phosphorylation

Aerobic metabolism of one molecule of
glucose
– Yields 38 ATP

Aerobic metabolism of one molecule of
glycogen
– Yields 39 ATP

Overall efficiency of aerobic respiration
is 40%
– 60% of energy released as heat!!!!!
Is Glucose the Only Fuel Source?

No
Fuels for Phosphorylation

Carbohydrates
– Glucose (6 carbon molecule)
– Glycogen (branched carbon molecules)
• Glucose stored in muscle cells and liver
• Glycogenolysis - makes carbons available for
metabolism
– Occurring in muscle cells - glucose stays in muscle cells
– Occurring in liver – glucose put into circulation
Fuels for Phosphorylation

Fats (18+ carbon molecule)
– Primarily fatty acids (FA)
• Stored as triglycerides
• Stored in muscle cells and in adipose cells
• Beta oxidation makes FAs available for Krebs
Cycle
– Release of FAs from adipose to blood stream
– Hormone initiated
– All working muscles have access to FAs via cellular
storage or via blood stream
Fuels for Phosphorylation

Proteins
– Amino Acids (AA)
– Storage is structural (no extra depot)
– Carbons are available
– Not a primary energy source during
exercise (too expensive)
– But usable – long duration exercise (up to
15%)
Fuels for Phosphorylation
What is common between all these fuel
sources?
- A 2 carbon molecule called…..
Acetyl Co-A
Relationship Between the Metabolism of
Proteins, Fats, and Carbohydrates
There’s one other potential fuel
source.
The Cori Cycle: Lactate As a Fuel
Source
Can You See the “Big Picture”
Regarding Aerobic ATP Production?
What’s it all about?
Does anybody know?
Here’s how I found out.
How is control maintained?
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
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
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
Electron transport Cytochrome Oxidase ADP, Pi
chain
ATP, NADH
ATP
Remember…..
1 cell = absolute
Whole body = not absolute
Where is there interaction between
energy systems?
Interaction Between Aerobic and
Anaerobic ATP Production

Energy to perform exercise comes from an
interaction between aerobic and anaerobic
pathways
Interaction Between Aerobic and
Anaerobic ATP Production

Effect of duration and intensity
– Immediate movement
• Stored ATP
– Short-term, high-intensity activities
• Greater contribution of anaerobic energy systems
– ATP-PC and Glycolysis
– Long-term, low to moderate-intensity exercise
• Majority of ATP produced from aerobic sources
– Aerobic glycolysis, beta oxidation, protein
Questions?
End