Bioenergetics

Metabolism and Bioenergetics

• Nutrients from foods are the substrates for

metabolism and are provided and stored
as:

–Carbohydrate
–Fat
–Protein

• Each cell contains chemical pathways that

convert these substrates to usable energy,
a process called bioenergetics

Metabolism and Bioenergetics

• The energy we derive from food is stored in cells in the

form of adenosine triphosphate (ATP)

• ATP serves as the immediate source of energy for most

body functions including muscle contraction

Energy Sources

• During intense short-duration muscular effort, the body relies mostly on

carbohydrate to generate ATP

oAs exercise intensity increases we see a recruitment of fast twitch

muscle fibers

• Fast twitch are used to produce more force during high intensity exercise.
• They have high levels of glycolytic enzymes and few mitochondria, and few

lipolytic enzymes (fat breakdown)

• Longer, less intense exercise utilizes carbohydrates and fat for sustained

energy production

Multiple Choice

• During intense short-duration muscular effort, the body relies mostly on ________ to generate ATP

• protein

• fats

• carbohydrates

• calcium

Multiple Choice

Nutrients from foods are the substrates for metabolism and are provided and stored as:

• Carbohydrate

• Fat

• Protein

• all

Multiple Choice

The main storage molecule of energy in the body.

• ADP

• ATP

• Glucose

• Glycogen

Energy for Cellular Metabolism

Key Points

• We derive energy from food and store it as the high-

energy compound ATP

– Carbohydrate (4.1 kcal/g)
– Fat (9.4 kcal/g)
– Protein (4.1 kcal/g)

• Carbohydrate is stored as glycogen in muscles and the

liver and is more accessible than protein or fat

• Glucose, directly from food or broken down from

glycogen, is the usable form of carbohydrate

• Fat is stored as triglycerides in adipose tissue and

broken down to FFA

ATP Is Generated
Through 3 Energy Systems

1. ATP-PCr system
2. Glycolytic system
3. Oxidative system

Roles of N A D and F A D in electron transport

• Nicotinamide adenine dinucleotide (NAD)

• Oxidized form:
+

NAD+

• Reduced form: N A D H

• Flavin adenine dinucleotide (FAD)

• Oxidized form: F A D
• Reduced form:

FADH2

• Both NAD and FAD play an important role in transfer of

electrons

• Carrier molecules during bioenergetic reactions

15

Enzymes

• Enzymes are cellular proteins that act as catalysts to

increase the speed of reactions

• Lower the energy of activation

• Factors that regulate enzyme activity

• Temperature
• pH

• Interact with specific substrates

• Lock and key model

16

ATP-PCr System

• Your cells have a molecule other than ATP

that is capable of storing energy

• This is the high-energy phosphate molecule

called phosphocreatine (PCr)

• When PCr is broken down, the energy

produced helps to rebuild ATP from ADP

ATP is the Energy Currency

• ATP = Adenosine Triphosphate

• Made of a molecule of adenine and ribose (adenosine) and

linked to 3 phosphate molecules

• Energy for processes in the body

• Active transport, mechanical work, rebuilding the body

• Digestion, muscle contraction, nerve transmission, tissue

synthesis

PCr is the Energy Reservoir

• Only a small amount of ATP is actually

stored within the cell (~4 sec worth)

• Therefore, ATP must be continually re-

synthesized at the rate it is used if muscle
contraction is to continue

• PCr is stored in larger quantities than ATP

and provides energy for resynthesis

PCr is the Energy Reservoir

• Short bursts of exercise rely on PCr

• Mobilization of PCr is almost instantaneous and does not

require oxygen

ATP-PCr System

• Cells store small amounts of ATP, and

phosphocreatine (PCr), which is broken down to
regenerate ATP

• Release of phosphate from PCr is facilitated by the

enzyme creatine kinase

• The phosphate is donated to and ADP forming a

molecule of ATP

ATP-PCr System

• This process does not require oxygen (anaerobic)

• ATP and PCr sustain the muscle’s energy needs for 3-15

sec during an all-out sprint

• 1 mole of ATP is produced per one mole of PCr

ATP-PCr System

• The energy liberated during ATP breakdown is directly

transferred to other energy-requiring molecules

Eg. In the muscle, this energy activates specific sites

on the contractile elements causing the muscle fibres to
shorten

ATP-PCr System

• This is a fast process and doesn’t require any special

cellular structures

• This is an anaerobic process meaning oxygen is not

required

• During intense exercise, PCr levels deplete rapidly
• Therefore, the capacity to maintain ATP is limited

Creatine Supplementation
How might it work?

Creatine Supplementation

• Energy source in muscle for high intensity

• Found naturally in the body and in animal products

• Increases rate of muscle growth via performance effect and cell swelling

• Relative to placebo at 8 weeks. A Meta Analysis by Dempsey et al. (2002) showed

• 15 lbs increase in bench press strength
• 21 lbs increase in squat strength
• 1.8x increase in overall power

Nunes, 2017

Creatine

• Recommendation: 20g/day for 5 days and then 5g/day of creatine

monohydrate

The Glycolytic System

• Can only use carbohydrate as substrate
• Can occur without oxygen

Glycogen Breakdown and

Synthesis

Glycolysis
Breakdown of glucose; it may be anaerobic
or aerobic.
Glycogenesis
Glycogen is synthesized from glucose to be
stored in the liver or muscle.
Glycogenolysis
Glycogen is broken down into.

Glycolytic System

• ATP is also produced through the

breakdown of glucose/glycogen via
Glycolysis

• Can occur with or without oxygen present

(aerobic or anaerobic glycolysis

The Glycolytic System

• Requires 10-12 enzymatic reactions to

break down glycogen to lactic acid
producing ATP

• Occurs in the cytoplasm

• Glycolysis does not require oxygen

(anaerobic)

The Glycolytic System

• Without oxygen present, pyruvic acid

produced by glycolysis becomes lactic acid

• ATP-PCr and glycolysis provide the energy

for ~2 min of all-out activity

Glycolytic System

Glucose

Pyruvic Acid

with O2 present

Lactic acid
without O2

present

Glucose-6-
phosphate

Glycogen

12 enzyme
reactions

1 ATP Required

The Glycolytic System

• In order to generate energy, glucose or glycogen must be

converted to glucose-6-phosphate

• Glucose requires energy from one molecule of ATP to be

converted

• Glycolysis is ready to start once this glucose-6-phosphate

compound has been formed

The Glycolytic System

• Glycolysis produces pyruvic acid
• The pyruvic acid produced by anaerobic glycolysis

becomes lactic acid

• The amount of energy produced depends on whether the

original source was glucose or glycogen

The Glycolytic System

• 1 mole of glycogen produces 3 moles of ATP

• 1 mole of glucose produces 2 moles of ATP

because 1 mole is used to convert glucose
to glucose-6-phosphate

• Not a lot of ATP is generated but it is 2.5

times faster than the aerobic pathway

Which of these would result in the most
pyruvate being converted to lactic acid?

a) Swimming underwater as fast as you can
b) A 10 second sprint
c) Consuming a low carbohydrate diet prior to exercise
d) Doing a 1RM lift

ATP-PCr and Glycolytic Systems

Key Points

• ATP-PCr system

• Pi is separated from PCr by creatine kinase
• Pi is combined with ADP to form ATP
• Energy yield: 1 mole of ATP per 1 mole of PCr

• Glycolytic system

• Glucose or glycogen is broken down to pyruvic acid
• Without oxygen, pyruvic acid is converted to lactic acid
• 1 mole of glucose yields 2 moles of ATP
• 1 mole of glycogen yields 3 moles of ATP

Energy Sources for the Early Minutes of
Intense Exercise

• The combined actions of the ATP-PCr and glycolytic systems

allow muscles to generate force in the absence of
oxygen; thus these two energy systems are the major energy
contributors during the early minutes of high-
intensity exercise.

• Anaerobic glycolysis also produces a large amount of lactic

acid which in turn impairs the glycolytic enzymes

• This further inhibits breakdown of glycogen
• To exercise for longer than a few minutes, we need another

energy system

Aerobic ATP production 1

• Aerobic ATP results from cooperation between the citric

acid cycle and election transport chain (mitochondria)

• Citric acid cycle

• Completes oxidation of fuels (For example, fats, C H O,

proteins) to provide electrons for electron transport chain

• Electron transport chain

• Energy obtain from electron transport is used to produce A T

P at the end of the electron transport chain

46

Roles of N A D and F A D in electron transport

• Nicotinamide adenine dinucleotide (NAD)

• Oxidized form:
+

NAD

• Reduced form: N A D H

• Flavin adenine dinucleotide (FAD)

• Oxidized form: F A D
• Reduced form:

2
FADH

• Both NAD and FAD play an important role in transfer of

electrons

• Carrier molecules during bioenergetic reactions

48

Aerobic metabolism: Oxidative
phosphorylation

• Can use:

• Glucose/glycogen
• Fat
• Protein

• Requires oxygen
• Takes place in the

mitochondria

• Primary source of fuel

at rest

What Determines Which Energy System is
Predominantly Used?

1. Intensity of Exercise
2. Duration of Exercise
3. Fitness of the Participant

Oxygen deficit and excess post-exercise O2 consumption (E
P O C)

• Fig 4.4
•Access the text alternative for slide images.

57

Mechanisms responsible for rapid and slow components of E P O C

• Rapid portion of EPOC

• Elevated O2 consumption used for:

• Re-synthesis of stored PC in muscle

• Replenishing muscle (myoglobin) and blood (hemoglobin) O2 stores

Slow portion of O2 debt
• Increased O2 needed for elevated heart rate and breathing
• Increased body temperature = increased metabolic rate
• Increased blood levels of epinephrine and norepinephrine =

increased metabolic rate

• Conversion of lactic acid to glucose (gluconeogenesis)

58