Bioenergetics

Bioenergetics and Energy systems

PHTH 606

Terminology

Metabolism- Sum of all chemical reactions that occur
in the body

■Anabolic reaction- synthesis of new
molecules

■Catabolic reaction - breakdown of
molecules

Substrates- molecules acted on by enzymes in
chemical reactions that result in manufacture of end
products

Oxidation - removal of an electron from a
molecule or atom

Reduction - addition of an electron

Oxidation reduction reactions

Energy- capacity to do work

Thermodynamics- science of energy transfer

Bioenergetics - science of converting food substrate to energy

Bioenergetics

●

ATP
○

The form of energy used by the
body is called adenosine
triphosphate ( ATP) and is
considered the body’s energy
currency. When used it liberates
calories - which are defined as
units of energy.

○

ATP is formed by combining ADP
and inorganic phosphate ( Pi)

through a reaction catalyzed by
the enzyme ATPase

ATP

●Synthesis of ATP requires energy from
catabolism of other molecules
( ie muscle glycogen)

○Part of that energy is stored in the bond
between ADP and Pi

■During exercise that high energy bond
is broken and used for biological
process 9 ( muscle contraction )

Hydrolysis(cont)

●

The enzyme ATPase promotes the splitting of ATP and the high
energy phosphate bond releasing 7.3kcal of energy

●

Breakdown of ATP into ADP and Pi is commonly referred to as hydrolysis
due to the involvement of the H2O molecule in the reaction

●

During recovery or lower bouts of exercise ATP can be replenished by
reversal of joining ADP and Pi in a reaction driven by presence of
energy

ATP

●

ATP provides the energy required
for the work of repeated muscle
contraction, however the body only
stores small amounts of ATP
within the cells

●

Therefore we rely on rapid
regeneration of ATP when any work
is performed

●

If ATP can not be rapidly
regenerated , the stores of ATP
would quickly be depleted during
high intensity exercise scenarios
…

ATP

●

The demand for ATP from skeletal
muscle contraction stresses cellular
homeostasis

●

Disruption of ATP stores
→stimulates ↑metabolism and
sets in motion all of the
biochemical reactions needed to
maintain muscle ATP which
stimulate the energy pathways
to meet that ATP demand

Energy
Pathways

●Aerobic pathways are capable
of generating LARGE amounts
of ATP, Anaerobic pathways
generate smaller, more limited
quantities of ATP

●

Aerobic pathway generates ATP
SLOWER, whereas anaerobic has
capacity to generate ATP more
rapidly

●

Aerobic respiration occurs within the
mitochondria of the cell , whereas
anaerobic respiration takes place
within the cell sarcoplasm

Aerobic and anaerobic pathways can be differentiated by their
contributions to energy during different durations of exercise

Maximal rate of adenosine triphosphate (ATP)
regeneration for each energy system. Maximal rate of ATP
regeneration can be quantified by ATP turnover rate in
the units of millimoles per kilogram per second
(mmol/kg/sec)

Aerobic and anaerobic pathways can be
differentiated by their relative contributions to
maximal efforts of differing durations.

Let’s take a
closer look at the
anaerobic
pathways…

Phosphagen System or ATP-PC system
●

Most rapid way to generate ATP

●

Physical activity/ high intensity exercise increases demand for ATP

●

Hydrolysis of ATP catalyzed by ATPase increases ADP

●

Increased levels of ADP activate enzyme creatine kinase which facilitates
hydrolysis of CrP to Cr +P and in process liberates energy

●

That energy is used to manufacture a molecule of ATP by adding phosphate to
ADP

Phosphagen system cont..

●

This process continues as long as demand
for ATP exists OR until concentrations of
CrP can no longer provide the energy

●

Skeletal muscle concentration of CrP is
limited and within approx 10 sec at near max
efforts, resting CrP stores become depleted

Phosphagen/ATP-
PC cont..

●

This system is trainable but it requires rest
to rebuild
○

Work to rest cycles

○

1:10/12

○

In this system,for every 1 sec of
“work” need to rest 10-12 seconds

●

High Intensity exercise repeated over
multiple bouts for short duration
○

Jump rope, short sprint, chopping
wood , pole vault

●

Creatine supplements work to augment
creatine, therefore enhance regeneration of
ATP, allowing high intensity effort to be
carried out for longer

Phosphagen

system

Effects of training

●After severe high intensity
workouts that can deplete
phosphagen system it can take
5-15 min to replenish CrP levels

○Active recovery shown to be more
effective in replenishing than
passive recovery

○Higher trained cardiorespiratory
systems recover more quickly due to
improved delivery of O2

○Phospho Creatinine levels restored
more quickly in slow twitch vs fast
twitch

Glycolysis
●Metabolic pathway that breaks down Muscle glycogen into 2 pyruvate ( 3 carbons) or 2
lactate

●Pyruvate is end product of glycolysis but is converted to lactate in absence of oxygen or is
shuttled to mitochondria for aerobic respiration

●Sequence of 10 reactions that involve intermediate compounds

●Uses energy to complete specific steps and also releases energy at specific steps that are used to
produce ATP

Glycolysis

●

Energy needed to start reaction
- 1 or 2 ATP molecules needed
○

If original carbohydrate
source is glucose, it
costs more energy to
transport therefore
costs 2 ATP

○

If original source was
glycogen which is already
stored in the muscle
, it only costs 1 ATP

Phase 1- Energy
investment

Glycolysis

●The enzyme phosphofructokinase (
PFK) is responsible in step 3 of
glycolysis where fructo-6 phosphate is
broken down to fructo-1,6
diphosphate

○Rate limiting enzyme

○Action of PFK uses 1 ATP

●PFK levels upregulated with intense
exercise - triggered by ↑ levels of ADP
and Pi

○PFK down regulated by increased ATP
PFK

Glycolysis Phase 2- Energy produced

●

Glycolysis energy production can be either Aerobic or Anaerobic

●

Lets focus on Anaerobic first:
○

The 6 Carbons of Glucose are broken down to (2) 3 carbon
pyruvates

In the absence of oxygen, the pyruvate
then breaks down to lactate

2 net ATP produced

Phase 1 requires 2 ATP

Phase 2 gets 4 ATP

Let’s take a
closer look at the
aerobic
pathways…

Glycolysis

Again, the 6 carbon glucose is broken
down into 2 pyruvates, but instead of
lactic acid being the end product,
because there is oxygen , the
pyruvate is then converted to acetyl
-coenzyme A ( CoA) and enters
mitochondria for cellular respiration
via the Kreb’s cycle

●As with anaerobic
glycolysis a net 2 ATP
will be produced with
Aerobic glycolysis if initial
substrate was glucose
and 3 ATP if initial
substrate was glycogen

Aerobic

Glycolysis

●Also in phase 2 of aerobic
glycolysis:
○2 NAD+ → NADH

●NAD+
○Nicotinamide adenine
dinucleotide

○Synthesized from
dietary niacin ( B3)

○Critical in transferring
hydrogen electrons and
driving krebs cycle

Aerobic

NADH

cont..

●During steady state exercise, NADH
electrons and protons are passed into the
mitochondria to generate ATP

●Under non steady state , or anaerobic
conditions , NADH electrons and protons are
passed back to pyruvate to form lactate

Kreb’s Cycle/Citric Acid cycle
●

NAD+ to NADH 3x in cycle
plus one more going from
pyruvate to CoA, so total
of 4 NADH

●

We also get 1 FADH
( flavin adenine dinucleide)

●

Also in the process we
give off 2 CO2

●

1 GTP/ATP ( guanosine
triphosphate)

Oxidative

phosphorylation

●

10 NADH ( 2 pyruvates , each
producing 4 , then another 2
from glycolysis) For each
NADH you get 3 ATP , so..
○

30 ATP from NADH

●

For each FADH you get 2
ATP , and you get 1 FADH
x 2 cycles
○

4 ATP from FADH

●

2 net ATP from glycolysis

●

2 net ATP from Krebs cycle

Grand total of 38
ATP

Cashing in the ATP

Overview of 3
energy systems
capable of
resynthesizing
ATP

Lactate

A bad reputation

●

At rest and under steady-state
exercise conditions, we maintain a
balance between lactate production
and removal
○

lactate can be converted back
to pyruvate within some cells
and can be used as substrate
(fuel) by others (e.g., heart, liver
, muscles)

Lactate

●
Higher intensities → capacity for
mitochondrial respiration is exceeded→↑
pyruvate is converted to lactate.
○
↑ exercise intensities → ↑ reliance on
rate of glucose transfers to pyruvate
through glycolysis to make ATP.

○
↑ rates of glycolysis→ pyruvate
produced faster than it can enter
into the mitochondria for
mitochondrial respiration.
■
Excess pyruvate that cannot
enter the mitochondria is
converted to lactate, which can
then be used as fuel elsewhere
in the body (e.g., heart, liver,
non exercising muscles).

Lactate

buffer

●Pyruvate converted to lactate by
accepting hydrogen ion

●Increased hydrogen ions from ATP
hydrolysis due to increased
exercise ( demand for ATP)
○↑ H ions causes drop in pH aka
acidosis
■Occurs with anaerobic
exercise

○Proton accumulation may also
negatively impact muscle
contraction by interfering with
Ca release by sarcoplasmic
reticulum

○Proton accumulation may also
cause muscle burn by
increasing receptor sensitivity

ATP hydrolysis

lactate

Lactate threshold and

accumulation

●

As exercise intensity
increases over steady state
a threshold is reached where
lactate accumulates and
cannot be cleared
○Lactate threshold
■Represents shift from
aerobic to anaerobic
metabolism

Lactate

clearance

● We can clear lactate by

several mechanisms
○Oxidative muscle fibers (
primarily type I)
■Reverse hydrolysis

○Cardiac muscle fibers

○Brain

○Cori cycle

● Clearance happens

relatively quickly and
does not make you sore

Lactate Clearance

When the amount of lactate in the blood reaches a lactate threshold, it
can get sent to the liver via the bloodstream where it gets converted
back to glucose via the Cori cycle

Let’s pull it all together …

Energy pathways

In a 100 m run , which of the following
makes most sense about fuel sources
and bioenergetics ?

ⓘ Start presenting to display the poll results on this slide.

In a soccer game which of the
following makes sense about fuel
sources and bioenergetics?

ⓘ Start presenting to display the poll results on this slide.

Lipid Oxidation

●

In addition to carbohydrates, the
oxidation of lipids also serves as
an important source of energy for
ATP production

●

Lipolysis: Is the breakdown of
a triglyceride (Splitting the
glycerol backbone from the
fatty acid chains)

●

Beta Oxidation: The Breakdown of
Free Fatty Acid Chains into Acetyl
CoA

●

These processes work together to
breakdown fat from adipose or from
food.

Big Picture

●

Lipids yield much more energy
than glucose , but they do

so

much more slowly and less
efficiently ( yield less ATP

per

molecule of O2) than glucose

●

Therefore Lipids are best
used when oxygen is readily
available and demand for
energy is low:

Low to moderate prolonged

exercise

Protein
Oxidation

●

Proteins can be catabolized and
eventually provide the free energy
required to manufacture ATP during
exercise conditions

●

Proteins must be broken down into
amino acids and can enter energy
pathway at different points ( glycolysis,
beta oxidation

and Krebs cycle)

●

Amino acid oxidation during short
duration, low intensity exercise in
negligible, however contributions
during short duration

high

intensity

exercise

can

be

substantial

●

Prolonged exercise with glycogen
depletion will elicit greater stimulus
for protein breakdown and amino acid
oxidation

Role of
macronutrients -
(fats ,
carbohydrates
and proteins) are
involved in
mitochondrial
respiration

Short term, high
Intensity training

●

High intensity training
increases phosphagen system
and glycolysis to rapidly
generate ATP:
○

Resting concentrations of CrP
are increased in skeletal
muscle following short term
HIIT

○

Creatine Kinase the rate
limiting enzyme of the
phosphagen system is
upregulated with training

Other benefits of
ST HIIT:

●

Stimulates Glycolysis:
○

Increases glucose
delivery to working
muscles

○

Increases resting
concentration of
muscle glycogen

●

Increases mitochondria
volume

●

Increases glucose delivery
and glycolysis

●

Increases type 1 ms fiber ?

Prolonged , submaximal
Endurance Training

Questions??

Questions?