BIOLOGICAL OXIDATION
&
PRINCIPLE OF ENERGY METABOLISM
EDITED & RECOMPOSED BY
Dr. Liniyanti D.Oswari MSc.
For Medical student, Sriwijaya University
Block 8
Citric Acid Cycle
Biological oxidation

Carbohydrate metabolism


Lipid metabolism


Glucose, rbc metabolism, glycogen, blood
glucose, diabetes
Plasma lipoproteins – CM, VLDL, LDL, HDL
Protein metabolism

Gluconeogenesis
Calories
Fat contains 9 calories per gram
 Protein contains 4 calories/gram
 Carbohydrates has 4 calories per
gram


(approximately)
Anabolism: Building Up

ATP produced during catabolism
drives anabolism.

Excess carbohydrates energy can
result in fat synthesis.

Humans synthesize 11 of 20 amino acids;
remaining 8 essential amino acids must be
provided by diet.
Anabolism



Large complex molecules are synthesized
from smaller precursors.
Building block molecules (amino acids,
sugars and fatty acids) are produced or
acquired from the diet.
Because anabolic processes include the
synthesis of polysaccharides and proteins
from sugars and amino acids, the
biosynthetic pathways increase order and
complexity, they require inputs of free
energy (ATP and NADPH).
Energy Flows
through ATP
and redox
carriers to
couple
Catabolic and
Anabolic
Pathways
Nonlinear Metabolic Pathways
Metabolism in Muscle
Glucose
Glycogen
Glycogenolysis
Ca2+
PKa
Lactate
BCAA
Ile, Val
Fatty acids
Glycolysis
No O2
G6P
Pyruvate
Krebs
cycle
b-Oxidation
Ca2+
PDH
Acetyl-CoA
Ca2+
ISDH, aKGDH
Production of ATP
Electron
Transport
Chain
Eric Niederhoffer
Carbohydrate metabolism









Glucose
Rbc metabolism
Glycogen
Blood glucose
Diabetes
Glucose
How does the body metabolise glucose?
How can we obtain energy from glucose?
How is energy derived from glucose?
Glucose

2 types of glycolysis:
 Aerobic g. and anaerobic g.
 Aerobic g. occurs when oxygen supply is sufficient
 Anaerobic g. occurs when oxygen supply is lacking

In aerobic g.:
 Oxygen status: sufficient oxygen supply
 Glucose → pyruvate → TCA → GTP, NADH & FADH2
 Substrate-level phosphorylation: GTP → ATP
 NADH & FADH2 → ETC → ATP:



1 NADH → 3 ATP
1 FADH2 → 2 ATP
Anaerobic g.:
 Oxygen status: insufficient oxygen supply
 Glucose → pyruvate → lactate
 Lactate is used via Cori cycle
Rbc metabolism







What is the source of energy for rbc?
Rbc has no mitochondria
Rbc depends entirely on glycolysis for ATP
Glycogen
How is glycogen metabolised by the body?
How can we obtain energy from glycogen?
How is energy derived from glycogen?
Glycogen

Glycogen is involved in 2 ways:



At high blood glucose level:


Glycogen synthesis (glycogenesis)
Glycogen breakdown (glycogenolysis)
Glycogen is synthesized and stored in liver and muscles
At low blood glucose level:


Glycogen is broken down (degraded) by enzymes to yield glucose
Two enzymes breakdown glycogen to glucose:



Branching enzyme
Straight chain enzyme
Liver vs. muscle glycogen:



Body has more liver glycogen than muscle glycogen
Liver glycogen is used to maintain blood glucose level
Muscle glycogen is used internally
Blood glucose

What is normal blood glucose level?

Note:




Blood glucose is determined under fasting condition
Plasma is used to determine glucose content
Quote values in mmol/L, or mg/dl
Normal fasting plasma glucose (FPG) is 4.2-6.2
mmol/L=70 – 110 mg/dl
Maintenance of blood glucose

Note:
 There are many factors which regulate blood glucose level
 Factors: insulin, liver, glucagon, epinephrine, etc

When we eat:
 At high blood glucose level, insulin is secreted
 Insulin causes cells to take up glucose
 Cells use glucose for energy

When we sleep:
 The liver maintains blood glucose (by hepatic glycogenolysis) to
within acceptable levels between 4.2-6.2 mmol/L =70-110 mg/dl
(fasting values)
Gluconeogenesis

What is gluconeogenesis?


Formation of glucose from non-glucose sources
such as C-skeletons of glucogenic amino acids
Under what conditions does this occur?

Gluconeogenesis occurs when blood glucose is
low
Lipogenesis and Lipolysis
Figure 24.14
Protein Metabolism

Deaminated amino acids are converted into:



Pyruvic acid
One of the keto acid intermediates of the Krebs
cycle
These events occur as transamination,
oxidative deamination, and keto acid
modification
OVERVIEW OF METABOLIC PATHWAYS
AND SYSTEMS OF ENERGY METABOLISM
Nucleic
Acids
GLYCOGEN
PROTEIN
Ribose-5-P
Glucose-6-P
b
b
Lactate
g
Urea
e
a
Glucose
f
d
c
TRIACYLGLYCEROLS
i
j
h
Amino
Acids
Free Fatty Acids
a
l
k
p
Pyruvate
Acetyl-CoA
m
o
n
Ketone
Bodies
Figure . Energy systems
ATP
Energy
The meaning of “energy” in energy
metabolism
In a haste to learn the individual reactions in a pathway, its
easy to lose sight of the purpose of the pathway. With energy
metabolism, the purpose is to generate energy, generally as ATP or
NADH or some high energy compound that will be used in a later
anabolic step. Glycolysis and Krebs cycle reactions have a high
number of kinase and dehydrogenase enzymes, respectively, for this
reason. This class of enzymes is intimately connected with energy
production and conservation. Pathways in the cytosol tend to be less
energy yielding, whereas those in the mitochondria are almost totally
devoted to energy production. This tutorial will bring you closer to
understanding why and how cells conserve energy. It will also help
you see the logic behind molecular energy calculations. As you listen
to your heart pump or move your arm to scratch your head, you
should be able to tell what purpose energy serves to life.
Hydrolysis Reactions
tend to be Strongly
Favorable
(Spontaneous)
Isomerization Reactions
Have Smaller Free
Energy Changes
Complete Oxidation of
Reduced Compounds is
Strongly Favorable
Thermodynamic Laws

The First Law of Thermodynamics.



A system’s internal energy can change only by the
exchange of heat or work with the surroundings.
A Statement of Conservation of energy.
The Second Law of Thermodynamics.



The entropy of an isolated system will tend to
increase to a maximum value.
The entropy of such a system will not decrease,sucrose will never “ de-diffuse” into corner of the
solution.
Entropy is a measure of the randomness or
disorder in a system.
What is energy conservation?
The terms energy conservation and energy generation tend to carry the
same meaning. Conservation implies “avoiding heat”, or channeling the energy
differential between reactants and products into the synthesis of a compound.
Because energy as heat cannot be exploited in an isothermal system, biological
systems have to conserve energy by biosynthesis. Suppose for example ATP is
hydrolyzed during a reaction (click 1). The standard energy differential between
reactants and products (Go’) of that reaction is 30.5 kJ/mol.
ATP + H2O
ADP + PO4
This means the environment of the cell gains 30.5 kJ of heat energy for each
mole of ATP hydrolyzed by water. Obviously, this is wasteful. To counter the
loss, ATP hydrolysis is coupled with the synthesis of a phosphorylated
compound. You saw this as a “coupled” reaction when ATP was needed to
produce glucose-6-PO4 or fructose 1,6-bisPO4 (click 1).
Glucose + ATP
Fructose-6-PO4 + ATP
Glucose-6-PO4 + ADP
Fructose 1,6-bisPO4 + ADP
Now you see that by making glucose-6-PO4 or fructose 1,6-bisPO4, the cell avoids
losing the larger part of the ATP hydrolysis energy as heat. This is energy
conservation. Click one to go on.
LIFE opposes ENTROPY, “S”:
2nd Law of Thermodynamics:
a) Entropy & energy: heat exchange-25 oC
25 oC
100 oC
25 oC
25 oC
37 oC
25 oC
x
25 oC
Direct vs Indirect Energy Production
The energy generated in metabolic pathways comes in two forms,
direct or indirect. Direct or “substrate level” refers to energy generated during
a particular reaction. The production of ATP by reacting ADP with PEP is an
example of this type (click 1)
COO
COO
C~OPO3= + ADP
C=O
CH2
CH3
+ ATP
Indirect refers to energy channeled into a compound that will return
the energy at a later step. High energy compounds such as acyl-phosphates
or thioesters fit this example. Another is NADH generated during oxidation
reactions in the cytosol or Krebs cycle. When L-malate is oxidzed by NAD+,
NADH is generated (click 1). NADH and FADH2 have trapped the electron
pair from the oxidation in their structures and will release the energy when
they themselves are oxidized.
COO
COO
:
C=O
HO-C-H
+
+ NAD
+ NADH + H+
:
CH2
CH2
COO
COO
Calculating energy yield in glycolysis
Calculating energy yield helps you see the energy phase of metabolism
in real numbers. Take for example the energy yield when glyceraldehyde-3-PO4
is oxidized to pyruvate. How much energy is conserved in this reaction? To
determine that number we need to know the pathway. We also need to know if
anaerobic or aerobic conditions prevail. First the pathway. There are 5 enzymecatalyzed reactions to consider (click 1).
glyceraldehyde-3-PO4 + PO4 + NAD+
1,3-bisPO4 glycerate + ADP
3-phosphglycerate
2-phosphoglycerate
PEP + ADP
glyceraldehyde-3-PO4 + PO4 + NAD+ + 2ADP
1,3-bisPO4 glycerate + NADH + H+
3-phosphoglycerate + ATP
2-phosphoglycerate
PEP + H2O
pyruvate + ATP + H2O
pyruvate + NADH + H+ + 2ATP + 2H2O
Removing the common terms on both sides yields a final equation (click 1).
We see that the phosphate on glyceraldehyde-3-PO4 and the inorganic PO4
both contribute to formation of ATP. Thus, 2 ATPs are formed by the 5
reactions. Under anaerobic conditions “two” represents the final yield. But, if
the reaction was carried out with oxygen and involved the mitochondria,
energy to the equivalent of 5 ATPs would result. Click 1 to see why.
Energy yield in the mitochondria
The mitochondria is the heart of aerobic metabolism. Electrons in
NADH and FADH2 are channeled into the electron transport system, which is
driven by O2. A large part of energy of oxidation of the electron transport
components is preserved in ATP. Each NADH generates the equivalent of 3
ATPs and each FADH2, 2 ATPs for each pair of electrons transferred to oxygen
(click 1).
O2
NADH
:
Electron transport
H2O
NAD
ATP
ATP
ATP
NADH from the cytosol yields its electrons indirectly via a shuttle. NADH
generated by the 3 NAD-linked dehydrogenases in the Krebs cycle provide
most of the energy. For example, each citrate molecule oxidized to CO2 and
H2O generates the equivalent of 36 ATPs. Click 1 to see how this value was
obtained.
Energy yield in the Krebs cycle
A cycle implies the last intermediate returns to the front. Each turn of the
Krebs cycle results in the loss of 2 carbons as CO2 and generates 3NADH, one
FADH2 and one GTP (click 1). A 2-carbon compound, such as the acetate group
on acetyl-CoA, therefore, yields 12 ATPs of energy.
Acetyl-CoA
citrate
oxaloacetate
isocitrate
CO2
NADH
NADH
a-ketoglutarate
malate
NADH
fumarate
CO2
succinyl-CoA
FADH2
GTP
succinate
C4H4O5 + 31/2 O2
C6H8O7 + 41/2O2
C4H6O5 + 5 O2
4CO2 + 2H2O
6CO2 + 4H2O
4CO2 + 3H2O
Now, suppose instead of acetylCoA we want to determine the ATP yield
when oxaloacetate (OAA) is oxidized (click
1). First write the equation for the oxidation
(click 1). OAA yields 4 moles of CO2 for each
mole oxidized. Thus, 2 turns of the cycle are
needed to oxidize all of the carbons in OAA to
CO2. Two turns is equivalent to 24 ATPs.
Performing the same analysis for
citrate shows 6CO2 liberated, or 3 turns of the
cycle (click 1). Thus, citrate yield 36 ATPs, or
one third more energy than OAA. Finally lets
consider the oxidation of malate (click 1).
Malate has 4 carbons, which means the
oxidation will generate 4CO2. But, we also
need to oxidize malate to OAA, which
generates one NADH. Thus 3 more ATPs
than OAA, i.e., 24 + 3= 27 ATPs. Click 1 to
test and expand your understanding.
Thermodynamics and Metabolism
A. Free-Energy Change
• Free-energy change (G) is a measure of the
chemical energy available from a reaction
G = Gproducts - Greactants
• H = change in enthalpy
• S = change in entropy
Relationship between energy and entropy
• Both entropy and enthalpy contribute to G
G = H - TS
(T = degrees Kelvin)
-G = a spontaneous reaction in the
direction written
+G = the reaction is not spontaneous
G = 0 the reaction is at equilibrium
The Standard State (Go) Conditions
• Reaction free-energy depends upon conditions
• Standard state (Go) - defined reference conditions
Standard Temperature = 298K (25oC)
Standard Pressure = 1 atmosphere
Standard Solute Concentration = 1.0M
• Biological standard state = Go’
Standard H+ concentration = 10-7 (pH = 7.0) rather
than 1.0M (pH = 1.0)
B. Equilibrium Constants and
Standard Free-Energy Change
• For the reaction: A + B
C+D
Greaction = Go’reaction + RT ln([C][D]/[A][B])
• At equilibrium: Keq = [C][D]/[A][B] and
Greaction = 0, so that:
Go’reaction = -RT ln Keq
C. Actual Free-Energy Change Determines
Spontaneity of Cellular Reactions
• When a reaction is not at equilibrium, the
actual free energy change (G) depends
upon the ratio of products to substrates
• Q = the mass action ratio
G = Go’ + RT ln Q
Where Q = [C]’[D]’ / [A]’[B]’
The Free Energy of ATP
• Energy from oxidation of metabolic fuels is
largely recovered in the form of ATP
Go' = - RT ln K'eq
Variation of equilibrium constant with Go‘ (25 oC)
K'eq
G º'
kJ/mol
Starting with 1 M reactants &
products, the reaction:
10
4
- 23
proceeds forward (spontaneous)
10
2
- 11
proceeds forward (spontaneous)
100 = 1
10
10
0
is at equilibrium
-2
+ 11
reverses to form “reactants”
-4
+ 23
reverses to form “reactants”
Energy coupling


A spontaneous reaction may drive a non-spontaneous
reaction.
Free energy changes of coupled reactions are
additive.
A. Some enzyme-catalyzed reactions are interpretable as
two coupled half-reactions, one spontaneous and the
other non-spontaneous.
 At the enzyme active site, the coupled reaction is
kinetically facilitated, while individual half-reactions are
prevented.
 Free energy changes of half reactions may be
summed, to yield the free energy of the coupled
reaction.
For example, in the reaction catalyzed by the Glycolysis
enzyme Hexokinase, the half-reactions are:
ATP + H2O  ADP + Pi
Go' = -31 kJ/mol
Pi + glucose  glucose-6-P + H2O
Go' = +14 kJ/mol
Coupled reaction:
ATP + glucose  ADP + glucose-6-P Go' = -17 kJ/mol
The structure of the enzyme active site, from which H2O is
excluded, prevents the individual hydrolytic reactions, while
favoring the coupled reaction.
B. Two separate reactions, occurring in the same cellular
compartment, one spontaneous and the other not, may be
coupled by a common intermediate (reactant or
product).
A hypothetical, but typical, example involving PPi:
Enzyme 1: A + ATP  B + AMP + PPi
Go' = + 15 kJ/mol
Enzyme 2: PPi + H2O  2 Pi
Go' = – 33 kJ/mol
Overall spontaneous reaction: Go' = – 18 kJ/mol
A + ATP + H2O  B + AMP + 2 Pi
Pyrophosphate (PPi) is often the product of a
reaction that needs a driving force. Its spontaneous
hydrolysis, catalyzed by Pyrophosphatase enzyme, drives
the reaction for which PPi is a product.
“High energy” bonds:
Compounds with “high energy bonds” are said to have
high group transfer potential.
For example, Pi may be spontaneously cleaved from
ATP for transfer to another compound (e.g., to a
hydroxyl group on glucose).
Potentially, 2 ~P bonds can be cleaved, as 2
phosphates are released by hydrolysis from ATP.
AMP~P~P  AMP~P + Pi
AMP~P  AMP + Pi
(ATP  ADP + Pi)
(ADP  AMP + Pi)
Alternatively:
AMP~P~P  AMP + P~P
P~P  2 Pi
(ATP  AMP + PPi)
(PPi  2Pi)

ATP often serves as an energy source.
Hydrolytic cleavage of one or both of the "high energy"
bonds of ATP is coupled to an energy-requiring (nonspontaneous) reaction.
AMP functions as an energy sensor & regulator of
metabolism.
When ATP production does not keep up with needs, a
higher portion of a cell's adenine nucleotide pool is AMP.
AMP stimulates metabolic pathways that produce ATP.
•
Some examples of this role involve direct allosteric
activation of pathway enzymes by AMP.
•
Some regulatory effects of AMP are mediated by the
enzyme AMP-Activated Protein Kinase.
A reaction important for equilibrating ~P among adenine
nucleotides within a cell is that catalyzed by Adenylate
Kinase:
ATP + AMP  2 ADP
The Adenylate Kinase reaction is also important because
the substrate for ATP synthesis, e.g., by mitochondrial ATP
Synthase, is ADP, while some cellular reactions
dephosphorylate ATP all the way to AMP.
The enzyme Nucleoside Diphosphate Kinase (NuDiKi)
equilibrates ~P among the various nucleotides that are
needed, e.g., for synthesis of DNA & RNA.
NuDiKi catalyzes reversible reactions such as:
ATP + GDP  ADP + GTP,
ATP + UDP  ADP + UTP, etc.
Inorganic polyphosphate
Many organisms store energy as inorganic
polyphosphate, a chain of many phosphate residues
linked by phosphoanhydride bonds:
P~P~P~P~P...
Hydrolysis of Pi residues from polyphosphate may be
coupled to energy-dependent reactions.
Depending on the organism or cell type, inorganic
polyphosphate may have additional functions.
E.g., it may serve as a reservoir for Pi, a chelator of
metal ions, a buffer, or a regulator.
Why do phosphoanhydride linkages have a high G
of hydrolysis? Contributing factors for ATP & PPi
include:

Resonance stabilization of products of
hydrolysis exceeds resonance stabilization of the
compound itself.

Electrostatic repulsion between negatively
charged phosphate oxygen atoms favors
separation of the phosphates.
Phosphocreatine (creatine
phosphate), another
compound with a "high
energy" phosphate linkage, is
used in nerve & muscle for
storage of ~P bonds.
O
-
O
CH3
H
N
P
O
-
C
N
O
CH2
C
NH2+
phosphocreatine
Creatine Kinase catalyzes:
Phosphocreatine + ADP  ATP + creatine
This is a reversible reaction, though the equilibrium constant slightly
favors phosphocreatine formation.

Phosphocreatine is produced when ATP levels are high.

When ATP is depleted during exercise in muscle, phosphate is
transferred from phosphocreatine to ADP, to replenish ATP.
O-
O-
O
C
C
CH2
PEP
O-
O
ADP ATP
OPO32H+
C
C
C
O-
O
OH
CH2
enolpyruvate
C
O
CH3
pyruvate
Phosphoenolpyruvate (PEP), involved in ATP
synthesis in Glycolysis, has a very high G of Pi
hydrolysis.
Removal of Pi from ester linkage in PEP is spontaneous
because the enol spontaneously converts to a ketone.
The ester linkage in PEP is an exception.
NH2
N
N
ester linkage
O
-O
P
O-
O
O
P
O-
N
O
O
P
O
CH2
O-
ATP (adenosine triphosphate)
adenine
O
H
H
OH
H
OH
H
N
ribose
Generally phosphate esters, formed by splitting out
water between a phosphoric acid and an OH group,
have a low but negative G of hydrolysis. Examples:
 the linkage between the first phosphate and the
ribose hydroxyl of ATP.
O
6 CH
2
4
OH
P
OH
O
5
H
O
H
OH
3
H
OH
CH2
H
CH
O
1
H
2
HO
OH
OH
OH
glucose-6-phosphate
CH2
O
P
O-
O-
glycerol-3-phosphate
Other examples of phosphate esters with low but
negative G of hydrolysis:

the linkage between phosphate & a hydroxyl
group in glucose-6-phosphate or glycerol-3phosphate.
O
Protein Kinase
OH + ATP
Protein
Protein
O
P
O- + ADP
OPi
H2O
Protein Phosphatase

the linkage between phosphate and the hydroxyl
group of an amino acid residue in a protein
(serine, threonine or tyrosine).
Regulation of proteins by phosphorylation and
dephosphorylation will be discussed later.
ATP has special roles in energy coupling & Pi transfer.
G of phosphate hydrolysis from ATP is intermediate
among examples below.
ATP can thus act as a Pi donor, & ATP can be synthesized
by Pi transfer, e.g., from PEP.
Compound
Go' of phosphate
hydrolysis, kJ/mol
Phosphoenolpyruvate (PEP)
-
Phosphocreatine
-
Pyrophosphate
-
ATP (to ADP)
-
Glucose-6-phosphate
-
Glycerol-3-phosphate
-
Kinetics vs Thermodynamics:
A high activation energy barrier usually causes
hydrolysis of a “high energy” bond to be very slow in
the absence of an enzyme catalyst.
This kinetic stability is essential to the role of ATP
and other compounds with ~ bonds.
If ATP would rapidly hydrolyze in the absence of a
catalyst, it could not serve its important roles in energy
metabolism and phosphate transfer.
Phosphate is removed from ATP only when the
reaction is coupled via enzyme catalysis to some other
reaction useful to the cell, such as transport of an ion,
phosphorylation of glucose, or regulation of an enzyme
by phosphorylation of a serine residue.
Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Cytoplasm
Intermediate step
Cytoplasm
Cytoplasm
Krebs cycle
Mitochondrial
matrix
Cytoplasm
ETC
Mitochondrial inner Plasma
membrane
membrane

ATP produced from complete oxidation of 1
glucose using aerobic respiration
Glycolysis
Intermediate
step
Krebs cycle
2
By oxidative
phosphorylation
From
From
NADH
FADH
(2X3)=6
0
0
(2X3)=6
2
(6X3)=18
(2X2)=4
Total
4
30
4
Pathway

By substratelevel
phosphorylation
36 ATPs are produced in eukaryotes.
Oxidation-Reduction







Oxidation: the loss of electrons
Reduction: the gain of electrons
Oxidation-reduction (redox) reaction: any
reaction in which electrons are transferred
from one species to another
Ared + Box
Aox + Bred
Look for ions that change in charge
i.e. Zn (s) + Cu2+  Zn2+ (aq) + Cu (s)
The Zn lost electrons …..


It was oxidized
So the Cu was reduced!
Oxidation-Reduction
 Remember:







“LEO the lion says GER”
Loss
Electrons
OXIDATION
Gain
Electrons
REDUCTION
Oxidation-Reduction









+4
+3
+2
+1
0
-1
-2
-3
-4

You Try It
Oxidized
Fe2+  Fe 3+

Reduced
OXIDIZED!
Cu 2+  Cu (s)
Hint: Cu (s) is Cu 0
REDUCED!
Oxidation-Reduction

Example: if we put a piece of zinc metal in a
beaker containing a solution of copper(II)
sulfate




some of the zinc metal dissolves
some of the copper ions deposit on the zinc metal
the blue color of Cu2+ ions gradually disappears
In this oxidation-reduction reaction

zinc metal loses electrons to copper ions
Zn(s)

2+
Zn (aq) + 2 e
Zn is oxidized
copper ions gain electrons from the zinc
2+
Cu ( aq) + 2 e
-
Cu( s)
Cu
2+
is red uced
Oxidation-Reduction

we summarize these oxidation-reduction
relationships in this way
electrons flow
from Zn to Cu2 +
Cu2 + (aq)
loses electrons ; gains electrons ;
is red uced
is oxidized
gives electrons tak es electrons
to Cu 2+ ; is th e from Zn; is th e
red ucing agent oxidizin g agent
Zn(s)
+
2+
Zn ( aq) + Cu( s)
Oxidation-Reduction

using these alternative definitions for the
combustion of methane
electrons are
transferred from
carbon to oxygen
CH4 (g)
gains O and loses
H; is oxidized
+
O2 (g)
gains H;
is reduced
is the reducing is the oxidizing
agent
agent
CO2 (g) + H2 O(g)
Oxidation-Reduction

Five important types of redox reactions



combustion: burning in air. The products of complete
combustion of carbon compounds are CO2 and H2O.
respiration: the process by which living organisms use
O2 to oxidize carbon-containing compounds to produce
CO2 and H2O. The importance of these reaction is not
the CO2 produced, but the energy released.
rusting: the oxidation of iron to a mixture of iron oxides
4Fe(s) + 3O2 ( g)


2Fe2 O3 ( s)
bleaching: the oxidation of colored compounds to
products which are colorless
batteries: in most cases, the reaction taking place in a
battery is a redox-reaction
Oxidation-Reduction Reactions

Reduced
organic
compounds
serve as fuels
from which
electrons can
be stripped off
during
oxidation
Reversible Oxidation of a Secondary
Alcohol to a Ketone



Many biochemical oxidation-reduction reactions
involve transfer of two electrons
In order to keep charges in balance, proton transfer
often accompanies electron transfer
In many dehydrogenases, the reaction proceeds by a
stepwise transfers of proton ( H+ ) and hydride ( :H- )
NAD and NADP are Common
Redox Cofactors



These are commonly called pyridine nucleotides
They can dissociate from the enzyme after the reaction
In a typical biological oxidation reaction, hydride from an
alcohol is transferred to NAD+ giving NADH
Heat of Reaction

In almost all chemical reactions, heat is either
given off or absorbed


example: the combustion (oxidation) of carbon
liberates 94.0 kcal per mole of carbon oxidized
C(s) + O2 (g)  CO2 (g) + 94.0 kcal
Heat of reaction: the heat given off or
absorbed in a chemical reaction


exothermic reaction: one that gives off heat –
feels hot
endothermic reaction: one that absorbs heat –
feels cold
Heat of Reaction

So, is this reaction exothermic or
endothermic?
C(s) + O2 (g)  CO2 (g) + 94.0 kcal
Heat is released (on the product side)
It’s Exothermic
How about:
2 NH3 + 22.0 kcal  N2 (g) + 3 H2 (g)
Heat enters with reactant (on the reactant side)
It’s Endothermic
What are Functions of NAD, NADP, FAD?
Electron carriers
Oxidation / reduction reactions
NAD and catabolic reactions
-- substrate oxidation
-- H- used for ATP synthesis
NADP and anabolic reactions
-- substrate reduction
-- e.g., --COOH to C=O to C-OH
Using NADH to make ATP
Electron transport and oxidative
phosphorylation
You should be able to complete a table to calculate energy yields from glucose or fatty acids (of any given length)
-- assuming 2.5 ATP per NADH (1.5 per glycolytic NADH) and 1.5 ATP per FADH
From glucose
Glycolysis
____ NADH x ____ ATP
____ ATP
Transition Rx
____ NADH x ____ ATP x 2 pyr
Krebs cycle
____ NADH x ____ ATP x 2 pyr
____ FADH x ____ ATP x 2 pyr
____ GTP x ____ ATP x 2 pyr
Total
ATP yield
_______
_______
_______
_______
_______
_______
30
From a 12 carbon fatty acid
B-oxidation
____ FADH x ____ ATP x 6 acCoA
____ NADH x ____ ATP x 6 acCoA
Krebs cycle
____ NADH x ____ ATP x 6 acCoA
____ FADH x ____ ATP x 6 acCoA
____ GTP x ____ ATP x 6 acCoA
Total
ATP yield
_______
_______
_______
_______
_______
84
What are the biosynthetic roles
Of these pathways?
Table . Summary of redox complexes of the electron transport chain
Complex designation
Electron transport function
Complex I (NADH-Q reductase)
Iron containing flavoprotein
oxidizes NADH to NAD+;
transfers electrons to coenzyme Q
Complex II (Succinate-Q reductase)
FAD prosthetic group; SDH
oxidizes succinate to fumarate;
electron transfer to CoQ
Complex III (cytochrome reductase)
Heme-iron cytochromes
reduces cytochrome C
electron transfer CoQ to cyt C
Complex IV (cytochrome oxidase)
Copper and iron containing heme
oxidizes cytochrome C;
reduces ½O2 to H2O
electron transfer cyt C to O2
CLINICAL CORRELATE – RESPIRATORY CHAIN DEFECT
defects in each complex of the respiratory chain have been identified
associated with lactic acidemia because the high NADH
concentration favors the formation of lactate from pyruvate
blood lactate may be elevated 30-fold
blood pyruvate increases up to 10-fold
NADH  inhibition of TCA cycle + PDH  pyruvate
pyruvate + NADH  Lactate
• ketones produced due to inhibition of TCA cycle and blood ratio of
b-hydroxybutyrate to acetoacetate increased in response to
increased mitochondrial NADH to NAD ratio
• serum alanine is also increased due to decreased pyruvate
metabolism
e- = electrons
CYTOPLASM
O2
OUTER
MEMBRANE
eCoQ
Glucose
NAD+
e-
GLYCOLYSIS
FADH2
NADH
eNAD+
Pyruvate
Dihydroxyacetone
phosphate
(DHAP)
(1)
Glycerol e3-phosphate
INNER
MEMBRANE
MATRIX
e-
DHAP
(2)
G3P
Glycerol-3-phosphate
dehydrogenase
FAD
Glycerol phosphate shuttle. Cytoplasmic glycerol 3-phosphate dehydrogenase
(1) oxidizes NADH. Glycerol 3-phosphate dehydrogenase in the inner membrane
(2) reduces FAD to FADH2.
Glucose
NAD+
e- = electrons
GLYCOLYSIS
INNER
OUTER MEMBRANE
MEMBRANE
e-
e-
Pyruvate
NADH
e-
OAA
(6)
Asp
NADH
Glu
Glu
(5)
eAsp
(4)
(3)
(1)
NAD+
OAA
Complex I
eMalate
KG
KG
(2)
CYTOPLASM
The malate-aspartate shuttle.
eMalate
NAD+
MATRIX
Mitochondrion
has two
membrane
bilayers
Inner mitochondria
membrane
Matrix
Cytochrome B, Cytochrome
C, Fe-S proteins, etc.
Electron Transport Chain
ATP
Synthase
NADH +
ATP production
NAD
Matrix
e.g. in brown fats for heat
generation in small mammals.
Oxidative Phosphorylation takes place in
mitochondria for more ATP production
• Glycolysis takes place in the cytoplasm; after glycolysis,
pyruvate is added with CoA using NAD+ to become Acetyl
CoA, CO2 and NADH.
• Acetyl CoA is the fuel for Krebs Cycle to take place in the
matrix.
• Oxidative phosphorylation depends on electron transfer and
the respiratory chain linking to TCA cycle create proton
gradient across the inner membrane of mitochondria.
• The proton gradient powers the synthesis of ATP using ATP
Synthase
• When these steps are blocked or uncoupled by uncoupling
proteins, no ATP made but only heat energy produced.
Summary
In this chapter, we learned that the rules of thermodynamics, and organic
chemistry still apply to living systems.
For example:
• Group transfer reactions are favorable when the free energy of products
is much lower than the free energy of reactants. In biochemical
phosphoryl transfer reactions, the good phosphate donors are
destabilized by electrostatic repulsion, and the reaction products are
often stabilized by resonance.
• Unfavorable reactions can be made possible by chemically coupling a
highly favorable reaction to the unfavorable reaction. For example, ATP
can be synthesized in the cell using energy in phosphoenolpyruvate.
• Oxidation-reduction reaction commonly involve transfer of electrons from
reduced organic compounds to specialized redox cofactors. The
reduced cofactors can be used in the biosynthesis, or may serve as a
source of energy for ATP synthesis.
Review Questions
• How does muscle produce ATP
(carbohydrates, fatty acids,
branched-chain amino acids)?
• What are the key Ca2+ regulated
steps?
Test and Expand your understanding about energy
1. How many phosphorylated intermediates are in the Krebs cycle?
Ans: None. GTP is synthesized from GDP + Pi. GTP, however, is not a cycle
intermediate.
2. How is ATP generated in the Krebs cycle?
Ans: Indirectly. The reduced coenzymes, NADH and FADH2 shuttle electrons to the
electron transport system and energy is preserved by ATP synthesis
3. Is pyruvate → acetyl-CoA the only way to enter carbons into the Krebs cycle?
Ans: No. Any compound that can be converted into a Krebs cycle intermediate will
contribute carbons to the Krebs cycle. This applies to aspartate and glutamate,
which form OAA and a-ketoglutarate, respectively.
4. What numbers should I remember in order to calculate energy yield in the
Krebs cycle?
Ans: In terms of ATP, remember that each NADH is equivalent to 3, each FADH2 to 2,
and each turn of the cycle 12 ATPs.
5. How many ATPs are generated when succinyl-CoA is oxidized in the cycle?
Ans: 30. One for GTP, two for FADH2 and 3 for NADH must be added to the 24 for 2
turns of the cycle.
Kebutuhan energi Manusia
• Gambaran
Kkal/hari
•
•
•
•
•
•
Energi digunakan
Wanita dewasa normal
Laki-laki dewasa normal
Pasien Bed rest
Bayi baru lahir
Remaja perempuan aktif
Remaja pria aktif
700 – 2000
2400 – 2800
1300 – 1800
350 – 450
2400 – 2600
3100 - 3600
Energi yang digunakan
•
•
•
•
•
•
Aktifitas
Kkal/mnt
Duduk sambil istirahat 0.7 – 2.0
Berjalan
2.0 – 6.0
Lari cepat
15 atau lebih
Lari jarak jauh/Maraton 10 atau lebih
Balap sepeda
10 atau lebih
Total Energy Requirement
(Adults)(TERA)
• Energy Allowance Based on Activity Level
TERA = IBW (k) x Physical Activity
Activity level:
Bed rest (hospital patients)
27.5
Sedentary (mostly sitting)
30.0
Light (Tailor, Nurse, Physician, Jeepney driver)
35.0
Moderate (Carpenter, Painter, Heavy housework)
40.0
Very active (swimming, lumberman)
45.0
Rumus Harris Bennedict
•
•
•
•
Biasanya menghitung BMR melalui rumus sbb:
BEE = Basal Energy expenditure
Harris Bennedict
BEE female: 655 + 9.7( W kg)+1.85 (Ht cm)–
4.7(A)
• BEE male: 66.5 + 13.75 (W kg) + 5(Hg cm)–6.8
(A)
• Total Energy: BEE + Physical activity + TEF
Faktor yang mempengaruhi
BMR(Basal Metabolic Rate)
• Meningkat:
– Pertumbuhan
– Badan Kurus & Tinggi
– Laki-laki > Perempuan
– Demam , stress
– Kehamilan /menyusui.
– Meningkat pada thyroxin (
Thyrotoxocosis
Thermal Effect of Food
• TEF = Thermal effect of food
• Meningkat energi yang digunakan
setelah makan..
• 5-10% of BMR
• Digunakan untuk mencerna,
pencernaan dan asimilasi dari
Makanan Yang dimakan
• Contoh: 5% x 1320 = 60 Cal
Total Energy(TE)
• TE = BMR +TEF + Activities
• Aktifitas: Apa saja kegiatan rutin
– Sedentary 25-35% BMR
– Light 35-50%
– Moderate 50-70%
– Heavy >70%
– http://www.americaonthemove.org/
– USATODAY.com - Study: Obesity rises faster
in poor teens