Cellular respiration
AP Biology
Cellular Respiration
Stage 1:
Glycolysis
AP Biology
2007-2008
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2007-2008
Glycolysis
 Breaking down glucose

“glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C

ancient pathway which harvests energy
 where energy transfer first evolved
 transfer energy from organic molecules to ATP
 still is starting point for ALL cellular respiration

but it’s inefficient
 generate only 2 ATP for every 1 glucose

occurs in cytosol
AP Biology
That’s not enough
ATP for me!
In the
cytosol?
Why does
that make
evolutionary
sense?
Evolutionary perspective
 Prokaryotes

first cells had no organelles
Enzymes
of glycolysis are
“well-conserved”
 Anaerobic atmosphere


life on Earth first evolved without free oxygen (O2)
in atmosphere
energy had to be captured from organic molecules
in absence of O2
 Prokaryotes that evolved glycolysis are ancestors
of all modern life

AP Biology
ALL cells still utilize glycolysis
You mean
we’re related?
Do I have to invite
them over for
the holidays?
Overview
glucose
C-C-C-C-C-C
10 reactions
enzyme
2 ATP
enzyme
2 ADP
convert
fructose-1,6bP
glucose (6C) to
P-C-C-C-C-C-C-P
enzyme
enzyme
2 pyruvate (3C)
enzyme
DHAP
G3P
 produces:
4 ATP & 2 NADH P-C-C-C C-C-C-P
2H
 consumes:
2Pi enzyme
2 ATP
enzyme
 net yield:
2Pi
enzyme
2 ATP & 2 NADH

DHAP = dihydroxyacetone phosphate
AP Biology
G3P
= glyceraldehyde-3-phosphate
pyruvate
C-C-C
2 NAD+
2
4 ADP
4 ATP
Glycolysis summary
endergonic
invest some ATP
ENERGY INVESTMENT
-2 ATP
ENERGY PAYOFF
G3P
C-C-C-P
4 ATP
exergonic
harvest a little
ATP & a little NADH
like $$
in the
bank
NET YIELD
AP Biology
net yield
2 ATP
2 NADH
1st half of glycolysis (5 reactions)
Glucose “priming”

get glucose ready
to split
 phosphorylate
CH2 O
O
P
Glucose 6-phosphate
2
P O
ADP
CH2 O
O
P
CH2
CH2
CH2OH
O
Fructose 1,6-bisphosphate
O CH2
C
4,5 aldolase
isomerase
O Dihydroxyacetone
CH2OH phosphate
Glyceraldehyde 3
-phosphate (G3P)
Pi
NAD+
Pi
6
glyceraldehyde
NADH
NADH
3-phosphate
P
dehydrogenase
1,3-Bisphosphoglycerate 1,3-Bisphosphoglycerate
(BPG)
(BPG)
H
C
O
CHOH
CH2 O
NAD+
AP Biology
O
Fructose 6-phosphate
3
ATP
phosphofructokinase
split destabilized
glucose
P
ADP
phosphoglucose
isomerase
glucose
 molecular
rearrangement

CH2OH
Glucose
1
ATP
hexokinase
O
P
O
CHOH
CH2 O
P
O
P
2nd half of glycolysis (5 reactions)
DHAP
P-C-C-C
Energy Harvest

NADH production





G3P donates H
oxidizes the sugar
reduces NAD+
NAD+  NADH
NAD+
Pi
phosphorylation”
 ADP  ATP
AP Biology
NAD+
NADH
7
phosphoglycerate
kinase
ADP
ATP
3-Phosphoglycerate
(3PG)
ADP
ATP
3-Phosphoglycerate
(3PG)
8
phosphoglyceromutase
2-Phosphoglycerate
(2PG)
Phosphoenolpyruvate
(PEP)
CHOH
CH2
O P
C O
H C O
CH2OH
P
OH2O
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
ADP
ATP
Pyruvate
C
C
O
O
CH2
OC
ATP
Pyruvate
OC
O-
2-Phosphoglycerate
(2PG)
9
enolase
H2O
ADP
Payola!
Finally some
ATP!
Pi
6
NADH
ATP production
 G3P    pyruvate
 PEP sugar donates P
 “substrate level
G3P
C-C-C-P
O
C O
CH3
P
Substrate-level Phosphorylation
 In the last steps of glycolysis, where did
the P come from to make ATP?

9
the sugar substrateH O(PEP) enolase
OH2O
2
P is transferred
from PEP to ADP
kinase enzyme
ADP  ATP
AP Biology
Phosphoenolpyruvate
(PEP)
ADP
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
Pyruvate
I get it!
The Pi came
directly from
the substrate!
Pyruvate
C
CH2
O
O
OC
ATP
ATP
ATP
ADP
C
O
C O
CH3
P
Energy accounting of glycolysis
2 ATP
2 ADP
glucose      pyruvate
2x 3C
6C
4 ADP
4 ATP
2 NAD+
2
 Net gain = 2 ATP + 2 NADH


All that work!
And that’s all
I get?
But
glucose has
so much more
to give!
some energy investment (-2 ATP)
small energy return (4 ATP + 2 NADH)
AP 1Biology
6C sugar  2 3C sugars
Is that all there is?
 Not a lot of energy…

for 1 billon years+ this is how life on
Earth survived
 no O2 = slow growth, slow reproduction
 only harvest 3.5% of energy stored in glucose
 more carbons to strip off = more energy to harvest
O2
O2
O2
O2
AP Biology
O2
glucose     pyruvate
2x 3C
6C
Hard way
to make
a living!
But can’t stop there!
G3P
DHAP
NAD+
raw materials  products
Pi
+
NADH
NAD
NADH
Pi
1,3-BPG
NAD+
Pi
+
NADH
NAD
1,3-BPG
NADH
7
ADP
Glycolysis
6
Pi
ADP
ATP
ATP
3-Phosphoglycerate
(3PG)
3-Phosphoglycerate
(3PG)
2-Phosphoglycerate
(2PG)
2-Phosphoglycerate
(2PG)
glucose + 2ADP + 2Pi + 2 NAD+  2 pyruvate + 2ATP
+ 2NADH
8
 Going to run out of NAD+


9
H2O
without regenerating NAD+,
energy production would stop! Phosphoenolpyruvate
(PEP)
another molecule must accept HADP
10
from NADH
ATP
 so
AP Biology
NAD+ is freed up for another round
Pyruvate
H2O
Phosphoenolpyruvate
(PEP)
ADP
ATP
Pyruvate
How is NADH recycled to NAD+?
Another molecule
must accept H
from NADH
H2O
O2
recycle
NADH
with oxygen
without oxygen
aerobic respiration
anaerobic respiration
“fermentation”
pyruvate
NAD+
NADH
acetyl-CoA
CO2
NADH
NAD+
lactate
acetaldehyde
NADH
NAD+
lactic acid
fermentation
which path you
use depends on
AP Biology
who
you are…
Krebs
cycle
ethanol
alcohol
fermentation
REVIEW
10 reactions
glucose
C-C-C-C-C-C
2 ATP
2 ADP
convert
fructose-1,6bP
glucose (6C) to
P-C-C-C-C-C-C-P
2 pyruvate (3C)
DHAP
G3P
 produces:
4 ATP & 2 NADH P-C-C-C C-C-C-P
2H
 consumes:
2Pi
2 ATP
 net:
2Pi
2 ATP & 2 NADH

AP Biology
pyruvate
C-C-C
2 NAD+
2
4 ADP
4 ATP
Cellular Respiration
Stage 2 & 3:
Oxidation of Pyruvate and
the Krebs Cycle
AP Biology
2006-2007
Glycolysis is only the start
 Glycolysis
glucose      pyruvate
6C
2x 3C
 Pyruvate has more energy to yield



3 more C to strip off (to oxidize)
if O2 is available, pyruvate enters mitochondria
enzymes of Krebs cycle complete the full
oxidation of sugar to CO2
pyruvate       CO2
AP Biology
3C
1C
Mitochondria — Structure
 Double membrane energy harvesting organelle


smooth outer membrane
highly folded inner membrane
 cristae

intermembrane space
 fluid-filled space between membranes

matrix
 inner fluid-filled space


DNA, ribosomes
enzymes
 free in matrix &
What cells would have
AP
Biology
a lot
of mitochondria?
outer
intermembrane
membrane
inner
membrane-bound space
membrane
cristae
matrix
mitochondrial
DNA
Mitochondria – Function
Oooooh!
Form fits
function!
Dividing mitochondria
Membrane-bound proteins
Who else divides like that? Enzymes & permeases
bacteria!
What does this tell us about
the evolution of eukaryotes?
Endosymbiosis!
AP Biology
Advantage of highly folded inner
membrane?
More surface area for membranebound enzymes & permeases
Oxidation of pyruvate
 Pyruvate enters mitochondrial matrix
[
2x pyruvate    acetyl CoA + CO2
3C
2C
1C
NAD
Where
does the
CO2 go?
Exhale!
3 step oxidation process
 releases 2 CO2 (count the carbons!)
 reduces 2 NAD  2 NADH (moves e )
 produces 2 acetyl CoA


Acetyl CoA enters Krebs cycle
AP Biology
]
Pyruvate oxidized to Acetyl CoA
reduction
NAD+
Pyruvate
C-C-C
[
Coenzyme A
CO2
Acetyl CoA
C-C
oxidation
2 x Yield = 2C sugar + NADH + CO2
AP Biology
]
Krebs cycle
1937 | 1953
 aka Citric Acid Cycle
in mitochondrial matrix
 8 step pathway

Hans Krebs
 each catalyzed by specific enzyme
1900-1981
 step-wise catabolism of 6C citrate molecule
 Evolved later than glycolysis

does that make evolutionary sense?
 bacteria 3.5 billion years ago (glycolysis)
 free O2 2.7 billion years ago (photosynthesis)
 eukaryotes 1.5 billion years ago (aerobic
AP Biology
respiration = organelles  mitochondria)
Count the carbons!
pyruvate
3C
2C
6C
4C
This happens
twice for each
glucose
molecule
4C
citrate
oxidation
of sugars
4C
6C
CO2
x2
4C
AP Biology
acetyl CoA
5C
4C
CO2
Count the electron carriers!
pyruvate
3C
6C
4C
NADH
This happens
twice for each
glucose
molecule
2C
4C
citrate
reduction
of electron
carriers
x2
4C
FADH2
4C
AP Biology
acetyl CoA
ATP
CO2
NADH
6C
CO2
NADH
5C
4C
CO2
NADH
So we fully
oxidized
glucose
C6H12O6

CO2
& ended up
with 4 ATP!
What’s the
point?
AP Biology
Electron Carriers = Hydrogen Carriers
H+
 Krebs cycle
produces large
quantities of
electron carriers
NADH
 FADH2
 go to Electron
Transport Chain!

AP Biology
What’s so
important about
electron carriers?
H+
H+
H+
+
H+ H H+
H+
ADP
+ Pi
ATP
H+
Energy accounting of Krebs cycle
4 NAD + 1 FAD
4 NADH + 1 FADH2
2x pyruvate          CO2
3C
3x 1C
1 ADP
1 ATP
ATP
Net gain = 2 ATP
= 8 NADH + 2 FADH2
AP Biology
Value of Krebs cycle?
 If the yield is only 2 ATP then how was the
Krebs cycle an adaptation?

value of NADH & FADH2
 electron carriers & H carriers
 reduced molecules move electrons
 reduced molecules move H+ ions
 to be used in the Electron Transport Chain
like $$
in the
bank
AP Biology
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
Cellular Respiration
Stage 4:
Electron Transport Chain
AP Biology
2006-2007
ATP accounting so far…
 Glycolysis  2 ATP
 Kreb’s cycle  2 ATP
 Life takes a lot of energy to run, need to
extract more energy than 4 ATP!
There’s got to be a better way!
I need a lot
more ATP!
AP Biology
A working muscle recycles over
10 million ATPs per second
There is a better way!
 Electron Transport Chain

series of proteins built into
inner mitochondrial membrane
 along cristae
 transport proteins & enzymes
transport of electrons down ETC linked to
pumping of H+ to create H+ gradient
 yields ~36 ATP from 1 glucose!
 only in presence of O2 (aerobic respiration)

AP Biology
That
sounds more
like it!
O2
Mitochondria
 Double membrane
outer membrane
 inner membrane

 highly folded cristae
 enzymes & transport
proteins

intermembrane space
 fluid-filled space
between membranes
AP Biology
Oooooh!
Form fits
function!
Electron Transport Chain
Inner
mitochondrial
membrane
Intermembrane space
C
Q
NADH
dehydrogenase
cytochrome
bc complex
Mitochondrial matrix
AP Biology
cytochrome c
oxidase complex
Remember the Electron Carriers?
Glycolysis
glucose
Krebs cycle
G3P
2 NADH
Time to
break open
the piggybank!
AP Biology
8 NADH
2 FADH2
Electron Transport Chain
Building proton gradient!
NADH  NAD+ + H
e
p
intermembrane
space
H+
H+
H  e- + H+
C
e–
NADH H
FADH2
NAD+
NADH
dehydrogenase
inner
mitochondrial
membrane
e–
Q
AP Biology
H+
e–
H
FAD
2H+ +
cytochrome
bc complex
1
2
O2
H2O
cytochrome c
oxidase complex
mitochondrial
matrix
What powers the proton (H+) pumps?…
Stripping H from Electron Carriers
 Electron carriers pass electrons & H+ to ETC


H cleaved off NADH & FADH2
electrons stripped from H atoms  H+ (protons)
 electrons passed from one electron carrier to next in
mitochondrial membrane (ETC)
 flowing electrons = energy to do work

transport proteins in membrane pump H+ (protons)
across inner membrane to intermembrane space
H+
+
H
H+
TA-DA!!
Moving electrons
do the work!
+
H
H+
H+
+
H+ H+ H
+
H+ H H+
C
e–
NADH
AP Biology
+
H
H+
Q
e–
FADH2
FAD
NAD+
NADH
dehydrogenase
e–
2H+
cytochrome
bc complex
+
1
2
O2
H2O
cytochrome c
oxidase complex
ADP
+ Pi
ATP
H+
But what “pulls” the
electrons down the ETC?
H 2O
O2
AP Biology
electrons
flow downhill
to O2
oxidative phosphorylation
Electrons flow downhill
 Electrons move in steps from
carrier to carrier downhill to oxygen
each carrier more electronegative
 controlled oxidation
 controlled release of energy

make ATP
instead of
fire!
AP Biology
“proton-motive” force
We did it!
 Set up a H+


H+
H+
H+
gradient
Allow the protons
to flow through
ATP synthase
Synthesizes ATP
ADP + Pi  ATP
Are we
there yet?
AP Biology
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
Chemiosmosis
 The diffusion of ions across a membrane

build up of proton gradient just so H+ could flow
through ATP synthase enzyme to build ATP
Chemiosmosis
links the Electron
Transport Chain
to ATP synthesis
So that’s
the point!
AP Biology
1961 | 1978
Peter Mitchell
 Proposed chemiosmotic hypothesis

revolutionary idea at the time
proton motive force
1920-1992
AP Biology
Pyruvate from
cytoplasm
Inner
+
mitochondrial H
membrane
H+
Intermembrane
space
Electron
transport
C system
Q
NADH
Acetyl-CoA
1. Electrons are harvested
and carried to the
transport system.
NADH
Krebs
cycle
e-
e-
FADH2
e-
2. Electrons
provide energy
to pump
protons across
the membrane.
e-
H2O
3. Oxygen joins
with protons to
form water.
1 O
2 +2
2H+
O2
H+
CO2
ATP
Mitochondrial
matrix
AP Biology
H+
ATP
ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
H+
ATP
synthase
Cellular respiration
2 ATP
AP Biology
+
2 ATP
+
~36 ATP
Summary of cellular respiration
C6H12O6 + 6O2







 6CO2 + 6H2O + ~40 ATP
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the ATP come from?
What else is produced that is not listed
in this equation?
 Why do we breathe?
AP Biology
Taking it beyond…
 What is the final electron acceptor in
Electron Transport Chain?
O2
 So what happens if O2 unavailable?
 ETC backs up
nothing to pull electrons down chain
 NADH & FADH2 can’t unload H

AP Biology
 ATP production ceases
 cells run out of energy
 and you die!
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007