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Energy and Life
• Energy must be released from food gradually.
• Energy must be stored in readily accessible forms.
• Release of energy from storage must be finely
controlled so that it is available exactly when and
where it is needed.
• Just enough energy must be released as heat to
maintain constant body temperature.
• Energy in a form other than heat must be available to
drive chemical reactions that are not favorable at
body temperatures.
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Spontaneous reactions release free energy, which is
available to do work. ∆G = ∆H – T∆S
Exergonic applies to the release of free energy,
represented by a negative ∆G. Exothermic applies to
the release of heat, represented by a negative ∆H.
Endergonic: A non-spontaneous reaction or process
that absorbs free energy and has a positive ∆G.
Free-energy change switches sign but keeps the same
magnitude for the reverse of a reaction.
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Graphical Representation of Exergonic/Endergonic
In an unfavorable reaction, the products have more energy
than the reactants. The opposite is true for a favorable one.
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Together, all of the chemical reactions that take
place in an organism constitute its metabolism.
Metabolic pathways may be linear, cyclic, or
spiral
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Catabolism: Metabolic reaction pathways that break down
food molecules and release biochemical energy.
Anabolism: Metabolic reactions that build larger biological
molecules from smaller pieces.
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The Stages of Metabolism: Conversion of Food into
Biochemical Energy
1.Digestion
2.Production of Acetyl-SCoA ( a common intermediate produced
from breakdown of all classes of food, carbo, lipids and proteins).
3.Citric Acid Cycle
4. Electron Transport Chain and ATP synthesis
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Overview:
Pathway
Of Glucose to
Acetyl-SCoA
Through Pyruvate.
We will look at the
features of Glycolysis
reactions
separately…..
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Metabolism of Triacylglycerols:
TAG’s undergo hydrolysis to give
Fatty acid and glycerol
Fatty acids undergo
►Resynthesis of triacylglycerols for
storage
►Conversion to acetyl-SCoA
Catabolic pathways in brown
And Anabolic pathways are shown
In blue.
We will look into overview of reactions
of β-oxidation of fatty acids separately..
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Amino Acid pool: The entire collection of free
amino acids in the body.
Amino acids are continuously entering the pool, not
only from digestion but also from the breakdown of
old protein, and are continuously being withdrawn
for synthesis of new nitrogen-containing
biomolecules.
Amino Acid metabolism is a complex pathway
consisting of many different pathways.
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Catabolic intermediates produced from Amino Acids
can enter the citric acid cycle in different stages of the cycle.
What are Ketogenic and Glucogenic A.A’s?
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The Citric Acid Cycle: a cyclic pathway of eight
reactions.
the details of this cycle separately….
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The Electron-Transport Chain & ATP
synthesis
•The electron transport system is a series of oxidation-reduction
(redox) reactions that transfers electrons and hydrogen ion from
one chemical complex to another. The series of reactions are
exergonic.
•Two agents that take part in this series are the coenzymes
NAD+ and FAD. Both are nucleotide derivatives.
•FAD stands for Flavin Adenine Dinucleotide. It is synthesized
in our bodies from the vitamin Riboflavin. Its oxidized form is
FAD and the reduced form is FADH2.
•NAD stands for Nicotinamide Adenine Dinucleotide.It is
synthesized in our bodies from the vitamin Niacin. The oxidized
form is NAD+ and the reduced form is NADH.
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Review: Redox reactions are loss/gain of
electrons.
OIL : Oxidation is Loss of electrons
RIG: Reduction is Gain of electrons
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Consider the following coupled redox reaction:
-O
O
C
+
NAD
+
H
C
H
C
-
OH
H
C
H
C
-O
O
H
C
+
NADH + H+
C
O
malate
O
O
-O
O
oxaloacetate
Two hydrogens and two electrons are removed from malate.
NAD+ takes both electrons and one hydrogen (it is reduced).
The other Hydrogen is without an electron and floating
around as H+
This is an example of a biochemical redox reaction.
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Later on in the Electron Transport Chain, NADH and H+ is going
to transfer the two electron and the hydrogen ion to FAD
Which becomes FADH2. This reaction releases energy.
Write this equation.
The NAD+ now regenerated is free to go back and pick up
more electrons and Hydrogens.
The FADH2 is ready to pass on its acquired electrons and
Hydrogen ions to the next complex.
The electron transport chain consists of enzymes in four complexes
held in fixed positions and the two coenzymes that carry electrons from one
complex to the next.
Enzymes of the electron transport chain are imbedded in the inner membrane
of mitochondria.
Ultimately, water will be produced from these hydrogen and electron and
The O2 we breathe in. Pearson Prentice Hall 2007
The ETC is an energetically
downhill process.Each enzyme
complex (I-IV) contains several
enzyme carriers.
The 5th complex contains ATP
Synthase which is made up of a
group of proteins which work
together to make ATP.
Final step is ATP production using
energy released during the ETC.
Note: Water is also being produced
More than 90% of the oxygen we
breathe is used in electron
transport–ATP synthesis reactions.
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Energy from three of the transfers is used to transport hydrogen
ions across the inner mitochondrial membrane to the intermembrane
Space.
The maintenance of this concentration gradient across the membrane
is crucial—it is the mechanism by which energy for ATP formation
is made available.
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Structures of Electron carriers in the ETC chain
This is a partial structure of NAD+.
The + sign comes from the quaternary N atom. In NADH a new C-H
bond is formed. One H+ is floating around.
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Structures of Electron carriers in the ETC chain
FAD picks up two electrons and two H ions
To form FADH2
Note the site of reduction.
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Structures of Electron carriers in the ETC chain
This molecule is also known as ubiquinone (two ketone groups).
Note the sites of redox reaction.
•Reminder:
Electrons are passed from weaker to increasingly stronger
oxidizing agents, with energy released at each transfer.
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Other important electron acceptors are various
cytochromes, which are proteins that contain heme
groups in which the iron cycles between Fe+2 and Fe+3
and proteins with iron–sulfur groups in which the iron
also cycles between Fe+2 and Fe+3 (only 1 e- transfer)
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Suggested Homework for Metabolic Pathways:
21.41 – 21.44, 21.47, 21.49, 21.53 a,b, 21.54 a,b, 21.55, 21.67, 21.74
23.26, 23.27, 23.39, 23.43 and 23.44, 23.45, 23.47, 23.48
25.16, 25.19, 25.26, 25.30-25.36,25.39 (in class), 25.40, 25.42
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The purpose of coupling two biochemical reactions is
to
A) lower the activation energies of both reactions.
B) convert an endergonic reaction to an exergonic one.
C) convert an exergonic reaction to an endergonic one.
D) use an endergonic reaction to drive an exergonic
reaction.
E) use an exergonic reaction to drive an endergonic
reaction.
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In the pathways for the digestion of food and the
production of biochemical energy, the oxidation of AcetylSCoA occurs in:
1. stage 1: digestion.
2. stage 2: Acetyl-SCoA
production.
3. stage 3: citric acid cycle.
4. stage 4: ATP production.
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All of the following molecules are
directly involved in the electron
transport chain except
A) coenzyme Q.
B) ADP.
C) cytochrome c.
D) acetyl-SCoA.
E) H2O.
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