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Metabolism
Thermodynamics
• Free Energy
• Activation Energy
Enzymes
ATP coupling
Factors on Enzymatic activity
• Optimal activity graphs
• Michealis Mentin Kinetics
Regulation
Reading
Ch 8: Energy
Homework
Ch 9 Prequiz
Cell Respiration prequiz
Check your clicker grades
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Extra Credit Science Seminar
Enzyme requirements – Cofactors
Low MW compounds at active site
Terms are not strictly held – usage not fixed
Cofactors are nonprotein enzyme helpers
- inorganic (such as a metal in ionic form) or organic
- Cofactors usually refers to inorganic
• Coenzyme - loosely bound organic cofactor
- Name stresses affect on enzyme
- include vitamins
• Prosthetic Group = covalently bound organic cofactor
- Name stresses the fact that it is tightly bound
- Function is partially to affect enzyme shape and partially for
interacting with substrates
Examples of cofactors
Only Cofactor
Carbonic anhydrase
Zn2+ surrounded by 3 x His
Also Covalently bound
So also a Prosthetic group
Cofactors
Transition metals
For redox reactions
Fe3+ + e-
Fe2+
Cu2+ + e-
Cu+
or other …
Generally when people say cofactor they mean
a metal ion
Organic Prosthetic groups
coenzymes
Derivative used as
prosthetic groups
Riboflavin
flavin adenine
dinucleotide (FAD+)
Vit B-1
Thiamine
Thiamine pyrophosphate
(THPP)
Vit B-3
Niacin
Nicotinamide adenine
dinucleotide (NAD+)
Vit B-6
Pyridoxal
Pyridoxal phosphate
Vit B-12
Cobalmin
adenosylcobalamine &
methylcobalamin
Vit B-2
Biotin (vit B-7)
Covalently bound to protein
Protein is modified
O
C
Used in carboxylases
Substrate + CO2
Protein
Examples of cofactors
Heme
Not a hydrogen bond
Coenzyme & Cofactor
Covalently bound, so just call it a
Prosthetic group
Enzyme Inhibitors / Activators
• Competitive inhibitors bind to the active site of
an enzyme, competing with the substrate
• Noncompetitive inhibitors bind to another part
of an enzyme, causing the enzyme to change
shape and making the active site less effective
 Allosteric Affect
– Examples of inhibitors include toxins, poisons, pesticides, and
antibiotics
• Activators – opposite of a noncompetitve
inhibitor
Allosteric Regulation of Enzymes
• Allosteric regulation may either inhibit or
stimulate an enzyme’s activity
• Allosteric regulation occurs when a regulatory
molecule binds to a protein at one site (away
from active site) and affects the protein’s
function at another site (active site)
Allosteric activators and inhibitors
Fig. 8-19
Affects availability
of substrate
Alters Km
Substrate
Active site
Competitive
inhibitor
Enzyme
Noncompetitive inhibitor
Normal binding
Allosteric effect
Affects Enzyme
activity
Alters Vmax
Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
Regulatory
site (one
of four)
Active site
(one of four)
Activator
Active form
Stabilized active form
Oscillation
Non- functional
active site
Inhibitor Stabilized inactive
Inactive form
form
Affects of competitive inhibitor
normal
Rate
Vmax
+ inhibitor
½ Vmax
Km
Km
+inhibitor
Km increases = “graph shifts right”
No change in Vmax
Substrate conc.
Less productive
There is no opposite of a competitive inhibitor
No competitive “activator”
But if you remove a competitive inhibitor…
Vmax
original
½ Vmax
Km
-inhibitor
Km
Km decreases = “graph shifts left” More productive
Substrate
Enzyme
Competitive
Inhibitor
Substrate
Rate is 5 / 5s
=1 reaction / sec
normal
Same conc. But slower
Rate is 2 / 5 sec
Rate has decreased even
though substrate
concentration remains
unchanged
Some competitive inhibitors are better than other
(don’t let go), but others can be “pushed out” or
competed out.
The more substrate around, the more chances to try
to bump out inhibitor or to get in there before the
inhibitor has a chance to bind
Why does it have the
same Vmax then?
At
V
the
ratio
would
be but
evenof
more
There
high
enough
be
some
concentrations
affect,
substrate
maxwill
extreme.
So Inhibitor
little to no
you
it
willessentially
be negligible.
end upwould
with this:
interference.
How non-competitve inhibitors, Allosteric activators
Cofactors, Coenzymes, Prosthetic groups work
These all work by affecting the enzyme itself
Cofactors, Coenzymes & Prosthetic groups are
REQUIRED portions of the enzyme.
• often required for proper protein folding
• typically required at the active site
-For bonding
-Supplies electrons or functional groups for the reaction
-Temporarily for E-S transient complexes
Non-competitve inhibitors and allosteric activators,
both change the protein structure to make them better
or worse.
Typically away from the active site
enzyme & substrate
Enzymes not requiring a cofactor
are only referred to as enzymes
s
or
different enzyme
s
Cofactors
Coenzyme
prosthetic group
•Holoenzyme – an enzyme when combined
with cofactor etc.
•Apoenzyme – enzyme that requires a cofactor
but does not currently have one bound
(NON-Functional)
No cofactor = 0 or negligible activity
Non-competitive inhibitors and activators
work by altering the protein shape.
Non-competitive inhibitor impairs
enzyme activity. Unlike removing a
cofactor, does not necessarily
completely inactivate enzyme.
s
Activator makes the enzyme better.
Improves the active site. Unlike
cofactors, without activators
enzymes still have some activity.
Affects of non-competitive inhibitor
or removal of a cofactor, coenzyme, prosthetic group
or allosteric activator
original
Vmax
Vmax +inhibitor
+ inhibitor
(non-competitive)
½ Vmax
½ Vmax +inhibitor
Km
Vmax decreases = “graph shifts down”
Less productive
No change in Km
Affects of allosteric activator
or addition of a cofactor, coenzyme, prosthetic group
or removal of a non-competitive inhibitor
Vmax +activator
+ activator
original
Vmax
½ Vmax +inhibitor
½ Vmax
Km
Vmax increases = “graph shifts up”
No change in Km
More productive
Substrate
Allosteric Affector
Non-competitve
inhibitor
Enzyme
Notice how substrate can not displace
a non-competiitve inhibitor
Substrate
Rate is 5 / 5s
=1 reaction / sec
Rate is 5 / 1 min
=0.08 reactions / sec
or effectively nothing
So why doesn’t Km change?
As with Vmax for competitive inhibitors, Km will change,
but it should be a negligible amount. This is less true than
for competitive inhibition, but for our understanding we
will be using the following assumption.
1 reaction / sec
Effectively or comparitively
0 reactions / sec
So why isn’t the curve flat?
Because you probably have a mixture
Inhibitor
No inhibitor
Conc
.1 M
Reactions per sec
.1 M
This tube has “x” number of
enzymes. All are active.
Represented by 2 enzymes.
Reactions per sec
This tube has the same
number of enzymes. But
some portion are inactivated
by inhibitor while others
remain inactive. The inactive
ones make essentially no
contribution. Represented by
one functional and one nonfunctional enzyme
Let’s use some made up numbers.
Substrate conc on left and rate below
Because you probably have a mixture
Inhibitor
No inhibitor
Conc
.0 M
.1 M
.2 M
.3 M
.4 M
.5 M
.6 M
.7 M
.8 M
.9 M
1.0 M
Reactions per sec
0
15
30
42
50
54
57
59
60
60
60
0
15
30
42
50
54
57
59
60
60
60
Active enzymes
should behave
the same at the
same conc
Reactions per sec
0
15
30
42
50
54
57
59
60
60
60
0
0
0
0
0
0
0
0
0
0
0
Because you probably have a mixture
Inhibitor
No inhibitor
Conc
.0 M
.1 M
.2 M
.3 M
.4 M
.5 M
.6 M
.7 M
.8 M
.9 M
1.0 M
Reactions per sec
0
15
30
42
50
54
57
59
60
60
60
0
15
30
42
50
54
57
59
60
60
60
Reactions per sec
Total
0
30
60
84
100
108
114
118
120
120
120
Total
0
15
30
42
50
54
57
59
60
60
60
0
15
30
42
50
54
57
59
60
60
60
0
0
0
0
0
0
0
0
0
0
0
Because you probably have a mixture
Inhibitor
No inhibitor
Conc
.0 M
.1 M
.2 M
.3 M
.4 M
.5 M
.6 M
.7 M
.8 M
.9 M
1.0 M
Reactions per sec
Total
0
0
0
30
15 15
60
30 30
84
42 42
100
50 50
108
54 54
114
57 57
118
59 59
120
60 60
120
60 60
120
60 60
Reactions per sec
Total
0
0
15
15
Km (0.2M)
30
30
at ½ Vmax
42
42
is the same
50
50
54
54
57
57
59
59
60
60
Vmax is
60
60
lower
60
60
0
0
0
0
0
0
0
0
0
0
0
Affects of non-competitive inhibitor
or removal of a cofactor, coenzyme, prosthetic group
or allosteric activator
original
Vmax
Vmax +inhibitor
+ inhibitor
(non-competitive)
½ Vmax
½ Vmax +inhibitor
Km
Vmax decreases = “graph shifts down”
Less productive
No change in Km
Affects of allosteric activator
or addition of a cofactor, coenzyme, prosthetic group
or removal of a non-competitive inhibitor
Vmax +activator
+ activator
original
Vmax
½ Vmax +inhibitor
½ Vmax
Km
Vmax increases = “graph shifts up”
No change in Km
More productive
If an enzyme lacks a necessary
cofactor, how will this affect the
enzyme kinetics?
a)Vmax up
b)Vmax down
c)Km up
d)Km down
How will a competitive inhibitor
affect an enzyme’s kinetics?
a)Vmax down
b)Km up
c)Km down
d)Curve Shifts left
How will a non-competitive inhibitor
affect an enzyme’s kinetics?
a)Vmax down
b)Km up
c)Km down
d)Curve Shifts left
Non-Michaelis-Menten Kinetics: Cooperativity
One example of non-Michaelis-Menten Kinetics
There are others, but this is the most significant
Michaelis-Menten
Single active site
Cooperativity
substrate
Multiple
active sites
&
Substrate is
an activator
Cooperativity
• form of allosteric regulation  amplifies enzyme activity
• binding of substrate to one active site stabilizes favorable
conformational changes at all other subunits
Substrate = activator
S-Curve
Enzyme exhibiting cooperativity
•Difference is in beginning representing initial low
substrate binding
•As substrate binds, activates enzyme, more
easily binds substrate
•Remainder of curve matches normal kinetics
Same affects from inhibitors, activators, etc
as in Michaelis Menten Kinetics: competitive
Vmax
unchanged
Removing
competitive
inhibitor
original
inhibitors
adding
competitive
inhibitor
½ Vmax
Km decreases
= “shift left”
More productive
Km
Km
Removing
competitive
inhibitor
Km
+ competitive
inhibitor
Km increases
=“shift right”
Less productive
•Non-competitive inhibitors
•activators, cofactors, coenzymes, prosthetic groups
Vmax -inhibitor
 Vmax
“shift up”
 productive
Removing non-competitive inhibitor
or adding activator (allosteric)
or adding cofactor / coenzyme / prosthetic group
Vmax
original
½ Vmax - inhibitor
Vmax +inhibitor
 Vmax
“shift down”
 productive
½ Vmax
Adding non-competitive inhibitor
or removing activator (allosteric)
or removing cofactor etc
½ Vmax
+ inhibitor
Km
unchanged
Feedback Inhibition
• In feedback inhibition, the end product of a
metabolic pathway shuts down the pathway
• Feedback inhibition prevents a cell from wasting
chemical resources by synthesizing more
product than is needed
Maintains a stable level of product
Need Ile
Too little?
Enzymes
produce Ile
Later when
enough Ile
Need to turn
off / down
enzymes
otherwise
overproduction
Post-Translational Modifications
Can affect enzyme activity
Example:
Proteolysis = protein cleavage (by proteases)
Ex: Zymogens = inactive precursor
Inactive
protease
active
Post-Translational Modifications
Phosphorylation - adding phosphate
• addition or removal can activate or repress
• Kinases (generally to add Pi)
• Phosphatases (generally to remove Pi)
•Reversible & Instantaneous
• added to Serine, Threonine, or Tyrosine
- All have alcohol group (-OH)
Chapter 9: Cellular Respiration
Harvesting Chemical Energy / making ATP
Broad overview of cell respiration
With emphasis on enzymes & metabolic pathways
Catabolic Pathways and
Production of ATP
• The breakdown of organic molecules is exergonic
• Aerobic respiration consumes organic molecules
and O2 and yields ATP
• Fermentation is a partial degradation of sugars
that occurs without O2
• Anaerobic respiration - similar, but consumes
compounds other than O2
Cellular respiration
• includes both aerobic and anaerobic respiration
but is often used to refer to aerobic respiration
• Although carbohydrates, fats, and proteins are
all consumed as fuel, it is helpful to trace
cellular respiration with the sugar glucose:
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
(ATP + heat)
The NET reaction
Stages of Cellular Respiration
Cellular respiration has 3(4) stages:
1. Glycolysis
2. Pyruvate oxidation
3. The citric acid cycle
Stepwise oxidation of
glucose
Releasing energy
captured in the form of:
 NADH
4. Oxidative phosphorylation
Each Phase is multi-step
Redox Reactions: Oxidation & Reduction
Chemical reactions that transfer electrons
Oxidation - substance loses electrons (is oxidized)
Reduction - substance gains electrons, (is reduced) (the
amount of positive charge is reduced)
•The electron donor is called the reducing agent
•The electron receptor is called the oxidizing agent
The transfer of electrons releases energy stored in
organic molecules
Fig. 9-UN1
becomes oxidized
(loses electron)
becomes reduced
Reducing agent
Causes Cl to be Oxidizing (gains electron)
reduced
agent
• Some redox reactions do not transfer electrons but
change the electron sharing in covalent bonds
• An example is the reaction between methane and O2
Because O is more electronegative than carbon there is a
release of energy
Fig. 9-3
Oxidation – so where are the electrons?
R
R
C
R
H
R
R
H
C
O
R
O
R
Where do they go?
What is reduced?
H
H
2H+ & 2e-
R
Electron
shuttling by:
Nicotinamide adenine
dinucleotide (NAD+)
NAD+  NADH + H+
NADP+  NADPH + H+
FAD
 FADH2
oxidized
reduced
ΔG° = 53 kcal/mole
2 e-’s and 2 H+ from substrates
P
NADP+
Dehydrogenases
Enzymes that redox using
NAD+/NADH & 2nd substrate
Take electrons and add to NAD+
Oxidize substrate 1 & Reduce NAD+
Or vice versa
Dehydrogenase
HCOOH
Formic Acid
Formic Acid
Dehydrogenase
Cell Respiration
Oxidation of C and Reduction of O
Reduction
C6H12O6 + 6 O2

Oxidation
6 CO2 + 6 H2O + Energy
(ATP + heat)
ΔG° = - 686 kcal/mole
But broken down in a
more controlled release
Stepwise oxidation
Each step releases significant energy
Nothing 100% efficient
Fig. 9-5
Electron shuttling by:
H2 + 1/2 O2
1/ O
2 2
2H
(from food via NADH)
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
Explosive
release of
heat and light
energy
Flour Mill
explosions
(a) Uncontrolled reaction
1/ O
2 2
(b) Cellular respiration
Fig. 9-6-3
The Stages of Cellular Respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Citric
acid
cycle
Pyruvate
oxidation
Oxidative
phosphorylation:
electron transport
& chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Glycolysis
•
•
•
•
Cytosol
Simplest metabolic pathway
Most cells do it
Considered most primitive biochem process
mitochondria not needed
• 10 steps  10 enzymes
Glycolysis : Splitting of sugar
2 phases
Investment Phase
4 ADP & 2 NAD+
2 ATP
Glucose
Payoff phase
2 G3P
(C3)
(C6)
2 ADP
BPG
2Pyruvate
(C3)
4 ATP
2 NADH + H+
Investment Phase
Coupling
C  D
ΔG° = 5 kcal/mol
ATP  ADP + Pi
ΔG° = -7.3kcal/mol
C + ATP  D + ADP + Pi ΔG° = -2.3kcal/mol
E  F
ΔG° = 14 kcal/mol
Cannot be coupled to ATP, but maybe another reaction
G  H
ΔG° = -3 kcal/mol
Can be coupled but probably isn’t because it is already spontaneous
Which of the
following is a
possible ΔG?
a)-4
b)1
c)2
d)3
Which of the following is a possible
ΔG for ONLY:
Pi + Glu  G6P
Remember you coupled
this to ATP hydrolysis
a)-5
b)3
c)8
d)11
ATP  ADP + Pi
ΔG°= -7.3
kcal/mole
ATP + Glu  G6P + ADP
ΔG° < 0
Fig. 9-8
Glucose  CO2
Glycolysis
Kreb’s
ΔG° -686 kcal/mol
Oxidative Phosphorylation
4 ADP & 2 NAD+
2 ATP
Glucose
2 G3P
2 ADP
2Pyruvate
4 ATP
2 NADH + H+
Glucose  Pyruvate ΔG° -140 kcal/mol
Glycolysis : Energy investment phase
Glucose + 2ATP
2 G3P + 2 ADP
Use up 2 ATP because:
Glucose + Pi
2ATP
2 G3P
ΔG is
positive
2 ADP + 2 Pi
•Also “priming” G6P allow more glucose into the cell
& Blocks glucose from leaking out
•2nd ATP Hydrolysis step is essentially irreversible
committing molecule to the rest of glycolysis
How many total ATP are produced
during glycolysis?
Payoff phase
Investment Phase
4 ADP & 2 NAD+
2 ATP
Glucose
a)-2
b)4
c)10
d)32
2 G3P
2 ADP
2Pyruvate
4 ATP
2 NADH + H+
How many NET ATP are
produced during glycolysis?
a)-2
b)2
c)10
d)32
Payoff phase
1st oxidation step
oxidized
•Dehydrogenase
NAD+ involved
Oxidation of C
Coupled to reduction
of NAD+
Glyceraldehyde3-phosphate
2 x
2 NAD+
2 NADH
aka
G3P
GAP
PGAL
6
Triose phosphate
dehydrogenase
2Pi
+ 2 H+
•Large energy release
2 x
1, 3-Bisphosphoglycerate
BPG
For G3P +Pi  BPG?
What is a feasible G?
Remember:
NAD+  NADH + H+
ΔG° = 53 kcal/mole
Glyceraldehyde3-phosphate
2 x
2 NAD+
a)-61
2 NADH
6
Triose phosphate
dehydrogenase
2Pi
+ 2 H+
b)-8
c)-2
d)+40
2 x
1, 3-Bisphosphoglycerate
G3P +Pi  BPG
ΔG° = ?
NAD+  NADH + H+
ΔG° = 53 kcal/mole
G3P + NAD+  BPG + NADH + H+
a)-61
b)-8
c)-2
d)+40
oxidized
R-CHO  R-COOH
NAD+
NADH
ΔG° -10.3 kcal/mol
Only that it is neg is important
Glyceraldehyde3-phosphate
2 x
2 NAD+
2 NADH
6
Triose phosphate
dehydrogenase
2Pi
+ 2 H+
2 x
1, 3-Bisphosphoglycerate
BPG
Fig. 9-9-6
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
2 1, 3-Bisphosphoglycerate
2 ADP
2
3-Phosphoglycerate
ΔG° 7.3
2 ATP
2
ΔG° -7.3 kcal/mol
7
Phosphoglycerokinase
3-Phosphoglycerate
Overall ΔG° -0.1 kcal/mol
Substrate level phosphorylation
Transfer of a phosphate from substrate to
ADP to generate ATP
R-P + ADP
R
+ ATP
• A smaller amount of ATP is formed in glycolysis and the
citric acid cycle by substrate-level phosphorylation
• Oxidative phosphorylation accounts for almost 90% of
the ATP generated by cellular respiration
Pi + ADP
ATP
Fig. 9-9-9
2 NAD+
Substrate Phosphorylation
6
Triose phosphate
dehydrogenase
2 Pi
2 NADH
+ 2 H+
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
Phosphoenolpyruvate
ΔG° -15 kcal/mol
2 ADP
2
3-Phosphoglycerate
8
Phosphoglyceromutase
2 ATP
2
10
Pyruvate
kinase
2-Phosphoglycerate
9
2 H2O
Enolase
2 Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
2
Pyruvate
Pyruvate
2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
Pyruvate
What is a possible free
energy change (ΔG) of
phosphoenolpyruvate to
pyruvate?
PEP  pyruvate + Pi
a)+5 kcal/mole
b)0
c) -5
d)-12
e)None of the above
What is the primary mechanism
of ATP generation in glycolysis?
a)ATP
b)NADP
c) substrate level phosphorylation
d)pyruvate
Which of the following is NOT a
product of glycolysis?
a)ATP
b)NADP
c)Lactic Acid
d)Pyruvate
Lactic acid fermentation
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
Lactic acid fermentation
• In lactic acid fermentation, pyruvate is reduced
to NADH, forming lactate as an end product,
with no release of CO2
• Lactic acid fermentation by some fungi and
bacteria is used to make cheese and yogurt
• Human muscle cells use lactic acid fermentation
to generate ATP when O2 is scarce
Why does a cell use fermentation?
a)To produce ATP
b) To produce lactic acid
c)To produce NAD+
d)To produce NADH
Fig. 9-8
How equilibrium affects Respiration
Normally (under aerobic conditions):
•Glucose resupplied
•Pyruvate & NADH used in next step
NADH + H+  NAD+
•ATP used for work
Anaerobic conditions (NO O2):
•Pyruvate & NADH not used (O2 is required)
• “Run out” of NAD+
Net
Glucose
2 ADP + 2 Pi
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Alcohol fermentation
2 ADP + 2
Glucose
P
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
Many other forms including production of
methane and hydrogen gas
What is the enzyme for alcohol fermentation?
a)Kinase
b)Phosphotase
c)Dehydrogenase
d)protease
?
Pyruvate decarboxylation &
citric acid (or kreb’s) cycle
completes the energy-yielding
oxidation of organic molecules
• In the presence of O2, pyruvate enters the
mitochondrial Matrix
• Before the citric acid cycle can begin, pyruvate
must be converted to acetyl CoA, which links
the cycle to glycolysis
Pyruvate oxidation
Step 1: pyruvate decarboxylation
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
2
1
Pyruvate
3
CO2
Coenzyme A
Acetyl CoA
Transport protein
/ pump
What is the enzyme?
Pyruvate Dehydrogenase
Fig. 9-10
Pyruvate  AcetylCoA is what
kind of reaction?
a)Substrate phosphorylation
b)Oxidative phosphorylation
c)condensation
d)Redox
Pyruvate dehydrogenase is likely
inhibited by:
Consider homeostasis
Consider feedback inhibition
O2 NADH
Glucose
NADH
a)pyruvate
b)ADP
c)ATP
d)O2
pyruvate
ATP
CO2
ATP is a competitive inhibitor, what will
happen to the enzyme kinetics of
pyruvate dehyrogenase as ATP builds up?
a)Vmax will go up
b)Vmax will go down
c)Km will shift right
d)Km will shift left
Pyruvate oxidation
Step 1: pyruvate decarboxylation
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
2
1
Pyruvate
3
CO2
Coenzyme A
Acetyl CoA
Transport protein
Oxidation  produces NADH
CoA carries 2 carbon unit to citric acid cycle
CO2 released
Fig. 9-10
AcetylCoA is starting material for Krebs cycle
• The citric acid cycle, also called the Krebs cycle,
takes place within the mitochondrial matrix
(except succinate dehydrogenase which is loosely
associated with inside membrane)
• The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn
• Complete oxidation of glucose  CO2
Fig. 9-12-8
CoA for next pyruvate
Acetyl CoA
CoA—SH
NADH
+H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
NADH
+ H+
3
CO2
Fumarate
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Pyruvate
CO2
NAD+
NADH
+ H+
Glycolysis
1 glucose  2 Pyruvates
2 NADH & 2ATP
CoA
Acetyl CoA
CoA
Pyruvate Decarboxylation
2 pyruvate  2 CO2
2 Acetyl CoA
2 NADH
Kreb’s
CoA
Citric
acid
cycle
FADH2
2 CO2
3 NAD+
3 NADH
+ 3 H+
FAD
ADP + P i
ATP
2 Acetyl  2 turns
1 turn 
•2 CO2
•3 NADH + H+
•1FADH2
•ATP
Total
4 CO2
6 NADH
2 FADH2
2 ATP
Before the krebs cycle, most of the
free energy from glucose was in:
a)Pyruvate
b)ATP
c)NADH
d)FADH
After the krebs cycle, most of the
free energy from glucose was in:
a)CO2
b)ATP
c)NADH
d)FADH
Fig. 9-8
Glucose  CO2
Glycolysis
Kreb’s
ΔG° -686 kcal/mol
Oxidative Phosphorylation
4 ADP & 2 NAD+
2 ATP
Glucose
2 G3P
2 ADP
2Pyruvate
4 ATP
2 NADH + H+
Glucose  Pyruvate ΔG° -140 kcal/mol
Lactic acid fermentation
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
Lactic acid fermentation
• In lactic acid fermentation, pyruvate is reduced
to NADH, forming lactate as an end product,
with no release of CO2
• Lactic acid fermentation by some fungi and
bacteria is used to make cheese and yogurt
• Human muscle cells use lactic acid fermentation
to generate ATP when O2 is scarce
Why does a cell use fermentation?
a)To produce ATP
b) To produce lactic acid
c)To produce NAD+
d)To produce NADH
Fig. 9-8
How equilibrium affects Respiration
Normally (under aerobic conditions):
•Glucose resupplied
•Pyruvate & NADH used in next step
NADH + H+  NAD+
•ATP used for work
Anaerobic conditions (NO O2):
•Pyruvate & NADH not used (O2 is required)
• “Run out” of NAD+
Net
Glucose
2 ADP + 2 Pi
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Alcohol fermentation
2 ADP + 2
Glucose
P
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
Many other forms including production of
methane and hydrogen gas
What is the enzyme for alcohol fermentation?
a)Kinase
b)Phosphotase
c)Dehydrogenase
d)protease
?
Pyruvate decarboxylation &
citric acid (or kreb’s) cycle
completes the energy-yielding
oxidation of organic molecules
• In the presence of O2, pyruvate enters the
mitochondrial Matrix
• Before the citric acid cycle can begin, pyruvate
must be converted to acetyl CoA, which links
the cycle to glycolysis
Pyruvate oxidation
Step 1: pyruvate decarboxylation
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
2
1
Pyruvate
3
CO2
Coenzyme A
Acetyl CoA
Transport protein
/ pump
What is the enzyme?
Pyruvate Dehydrogenase
Fig. 9-10
Coenzyme A
Carries acetyl groups
From vit B5
Pyruvate  AcetylCoA is what
kind of reaction?
a)Substrate phosphorylation
b)Oxidative phosphorylation
c)condensation
d)Redox
Pyruvate dehydrogenase is likely
inhibited by:
Consider homeostasis
Consider feedback inhibition
O2 NADH
Glucose
NADH
a)pyruvate
b)ADP
c)ATP
d)O2
pyruvate
ATP
CO2
ATP is a competitive inhibitor, what will
happen to the enzyme kinetics of
pyruvate dehyrogenase as ATP builds up?
a)Vmax will go up
b)Vmax will go down
c)Km will shift right
d)Km will shift left
Pyruvate oxidation
Step 1: pyruvate decarboxylation
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
2
1
Pyruvate
3
CO2
Coenzyme A
Acetyl CoA
Transport protein
Oxidation  produces NADH
CoA carries 2 carbon unit to citric acid cycle
CO2 released
Fig. 9-10
AcetylCoA is starting material for Krebs cycle
• The citric acid cycle, also called the Krebs cycle,
takes place within the mitochondrial matrix
(except succinate dehydrogenase which is loosely
associated with inside membrane)
• The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn
• Complete oxidation of glucose  CO2
Fig. 9-12-8
CoA for next pyruvate
Acetyl CoA
CoA—SH
NADH
+H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
NADH
+ H+
3
CO2
Fumarate
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Pyruvate
CO2
NAD+
NADH
+ H+
Glycolysis
1 glucose  2 Pyruvates
2 NADH & 2ATP
CoA
Acetyl CoA
CoA
Pyruvate Decarboxylation
2 pyruvate  2 CO2
2 Acetyl CoA
2 NADH
Kreb’s
CoA
Citric
acid
cycle
FADH2
2 CO2
3 NAD+
3 NADH
+ 3 H+
FAD
ADP + P i
ATP
2 Acetyl  2 turns
1 turn 
•2 CO2
•3 NADH + H+
•1FADH2
•ATP
Total
4 CO2
6 NADH
2 FADH2
2 ATP
Before the krebs cycle, most of the
free energy from glucose was in:
a)Pyruvate
b)ATP
c)NADH
d)FADH
After the krebs cycle, most of the
free energy from glucose was in:
a)CO2
b)ATP
c)NADH
d)FADH