Download Cellular Respiration

Making energy!
ATP
The point
is to make
ATP!
The energy needs of life
• Organisms are endergonic systems
• What do we need energy for?
• synthesis
• building biomolecules
• reproduction
• movement
• active transport
• temperature regulation
Where do we get the energy from?
• Work of life is done by energy coupling
• use exergonic (catabolic) reactions to fuel
endergonic (anabolic) reactions
+
+
+
energy
+
energy
Living economy
• Fueling the body’s economy
• eat high energy organic molecules
• food = carbohydrates, lipids, proteins, nucleic acids
• break them down
• catabolism = digest
• capture released energy in a form the cell can use
• Need an energy currency
• a way to pass energy around
• need a short term energy
storage molecule
ATP
ATP
• Adenosine Triphosphate
• modified nucleotide
• nucleotide =
adenine + ribose + Pi  AMP
• AMP + Pi  ADP
• ADP + Pi  ATP
• adding phosphates is endergonic
high energy bonds
How does ATP store energy?
AMP
ADP
ATP
O– O– O– O– O–
–O P –O
O– P –O
O––P
OO
P––O
O– P O–
O O O O O
• Each negative PO4 more difficult to add
• a lot of stored energy in each bond
• most energy stored in 3rd Pi
• 3rd Pi is hardest group to keep bonded to molecule
• Bonding of negative Pi groups is unstable
• spring-loaded
• Pi groups “pop” off easily & release energy
Instability of its P bonds makes ATP an excellent energy donor
How does ATP transfer energy?
O– O– O–
–O P –O
O– P –O
O– P O–
O O O
ADP
ATP
O–
–O P O – +
O
• ATP  ADP
• releases energy
• ∆G = -7.3 kcal/mole
• can fuel other reactions
• Phosphorylation
• released Pi can transfer to other molecules
• destabilizing the other molecules
• enzyme that phosphorylates = kinase
7.3
energy
An example of Phosphorylation…
• Building polymers from monomers
H H
C C
OHHO
• need to destabilize the monomers
• phosphorylate!
H
C
OH
H
C
OH
H
C
+
H
C
HO
+4.2 kcal/mol
“kinase”
+ ATP
+
P
H
C
HO
enzyme
-7.3 kcal/mol
-3.1 kcal/mol
enzyme
H H
C C
O
H
C
+
+
H2O
ADP
P
H H
C C
O
+
Pi
Another example of Phosphorylation…
• The first steps of cellular respiration
• beginning the breakdown of glucose to make ATP
glucose
C-C-C-C-C-C
hexokinase
phosphofructokinase
P
2 ATP
2 ADP
fructose-1,6bP
P-C-C-C-C-C-C-P
DHAP
P-C-C-C
G3P
C-C-C-P
C
C
H
C
P
ATP / ADP cycle
Can’t store ATP
 too reactive
 transfers Pi too
easily
 only short term
energy storage
 carbohydrates &
fats are long term
energy storage
ATP
respiration
7.3 kcal/mole
ADP + P
A working muscle recycles over
10 million ATPs per second
Cells spend a lot of time making ATP!
The
point is to make
ATP!
H+
ATP synthase
• Enzyme channel in mitochondrial
membrane
H+
H+
H+
H+
H+
H+
• permeable to H+
• H+ flow down
concentration gradient
• flow like water over
water wheel
• flowing H+ cause
ADP + P
change in shape of
ATP synthase enzyme
• powers bonding of
ATP
Pi to ADP
ADP + Pi  ATP
But… How is the proton (H+) gradient formed?
H+
rotor
rod
catalytic
head
H+
That’s the rest
of my story!
Any Questions?
Cellular Respiration
STAGE 1:
Glycolysis
Glycolysis
• Breaking down glucose
• “glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C
• most ancient form of energy capture
• starting point for all cellular respiration
• inefficient
• generate only 2 ATP for every 1 glucose
• in cytosol
• why does that make evolutionary sense?
Evolutionary perspective
• Life on Earth first evolved without
free oxygen (O2) in atmosphere
• energy had to be captured from
organic molecules in absence of O2
• Organisms that evolved glycolysis
are ancestors of all modern life
• all organisms still utilize
glycolysis
Overview
• 10 reactions
• convert
6C glucose
to two 3C
pyruvate
• produce 2
ATP & 2
NADH
glucose
C-C-C-C-C-C
2 ATP
2 ADP
fructose-6P
P-C-C-C-C-C-C-P
DHAP
P-C-C-C
PGAL
C-C-C-P
2 NAD+
2 NADH
4 ADP
4 ATP
pyruvate
2005C-C-C 2006
Glycolysis summary
endergonic
invest some ATP
exergonic
harvest a little
more ATP
& a little NADH
1st half of glycolysis (5 reactions)
• Glucose “priming”
• get glucose ready
to split
• phosphorylate
glucose
• rearrangement
• split destabilized
glucose
PGAL
2nd half of glycolysis (5 reactions)
• Oxidation
• G3P donates H
• NAD  NADH
• ATP generation
• G3P  pyruvate
• donates P
• ADP  ATP
OVERVIEW OF GLYCOLYSIS
1
2
3
6-carbon glucose
(Starting material)
2 ATP
P
P
6-carbon sugar diphosphate
P
P
6-carbon sugar diphosphate
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
2 ATP
3-carbon
pyruvate
Priming reactions. Priming
reactions. Glycolysis begins with
the addition of energy. Two highenergy phosphates from two
molecules of ATP are added to the
six-carbon molecule glucose,
producing a six-carbon molecule
with two phosphates.
P
NADH
2 ATP
3-carbon
pyruvate
Cleavage reactions. Then, the
Energy-harvesting reactions.
six-carbon molecule with two
phosphates is split in two,
forming two three-carbon sugar
phosphates.
Finally, in a series of reactions,
each of the two three-carbon
sugar phosphates is converted to
pyruvate. In the process, an
energy-rich hydrogen is harvested
as NADH, and two ATP molecules
are formed.
Substrate-level Phosphorylation
• In the last step of glycolysis, where
did the P come from to make ATP?
P is transferred
from PEP to ADP
 kinase enzyme
 ADP  ATP
Energy accounting of glycolysis
2 ATP
2 ADP
glucose      pyruvate
2x 3C
6C
4 ADP
4 ATP
• Net gain = 2 ATP
• some energy investment (2 ATP)
• small energy return (4 ATP)
• 1 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
• only harvest 3.5% of energy stored in glucose
• slow growth, slow reproduction
We can’t stop there….
 Glycolysis
glucose + 2ADP + 2Pi + 2 NAD+ 
2 pyruvate + 2ATP + 2NADH
• Going to run out of NAD+
• How is NADH recycled to NAD+?
• without regenerating NAD+,
energy production would stop
• another molecule must
accept H from NADH
NADH
20052006
How is NADH recycled to NAD+?
• Another molecule must accept H from NADH
• aerobic respiration
• ethanol fermentation
• lactic acid fermentation
• aerobic respiration
NADH
Anaerobic ethanol fermentation
• Bacteria, yeast
pyruvate  ethanol + CO2
3C
NADH
2C
1C
NAD+
 beer, wine, bread
 at ~12% ethanol, kills yeast
 Animals, some fungi
pyruvate  lactic acid
3C
NADH
3C
NAD+
 cheese, yogurt, anaerobic exercise (no O2)
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
Kreb’s cycle
mitochondria
What’s the point?
ATP
The Point is to Make ATP!
Cellular Respiration
Oxidation of
Pyruvate
Krebs Cycle
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 oxidation of sugar to
CO2
pyruvate       CO2
3C
1C
Cellular respiration
What’s the point?
ATP
The Point is to Make ATP!
Oxidation of pyruvate
• Pyruvate enters mitochondria
[
2x pyruvate    acetyl CoA + CO2
3C
2C
1C
NAD
•
•
•
•
NADH
3 step oxidation process
releases 1 CO2 (count the carbons!)
reduces NAD  NADH (stores energy)
produces acetyl CoA
• Acetyl CoA enters Krebs cycle
• where does CO2 go?
]
Pyruvate oxidized to Acetyl CoA
reduction
oxidation
Yield = 2C sugar + CO2 + NADH
Krebs cycle
1937 | 1953
• aka Citric Acid Cycle
• in mitochondrial matrix
• 8 step pathway
• each catalyzed by specific enzyme Hans Krebs
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
respiration (organelles)
Count the carbons!
pyruvate
3C
2C
6C
4C
This happens
twice for each
glucose
molecule
acetyl CoA
citrate
x2
4C
6C
oxidation
of sugars
CO2
5C
4C
4C
4C
CO2
Count the electron carriers!
pyruvate
3C
citrate
x2
4C
4C
acetyl CoA
6C
4C
NADH
This happens
twice for each
glucose
molecule
2C
6C
reduction
of electron
carriers
FADH2
4C
ATP
4C
CO2
NADH
5C
CO2
NADH
Whassup?
So we fully
oxidized
glucose
C6H12O6

CO2
& ended up
with 4 ATP!
20052006
NADH & FADH2
 Krebs cycle
produces large
quantities of
electron carriers
NADH
 FADH2
 stored energy!
 go to ETC

20052006
Energy accounting of Krebs cycle
4 NAD + 1 FAD
4 NADH + 1 FADH2
2x pyruvate          CO2
3C
3x 1C
1 ADP
• Net gain
1 ATP
= 2 ATP
= 8 NADH + 2 FADH2
So why the Krebs cycle?
• If the yield is only 2 ATP, then why?
• value of NADH & FADH2
• electron carriers
• reduced molecules store energy!
• to be used in the Electron Transport
Chain
Cellular Respiration
Electron Transport
Chain
Cellular respiration
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!
There is a better way!
• Electron Transport Chain
• series of molecules built into inner
mitochondrial membrane
• mostly transport proteins
• transport of electrons down ETC linked to ATP
synthesis
• yields ~34 ATP from 1 glucose!
• only in presence of O2 (aerobic)
Mitochondria
• Double membrane
• outer membrane
• inner membrane
• highly folded cristae*
• fluid-filled space
between membranes =
intermembrane space
• matrix
• central fluid-filled space
* form fits function!
Electron Transport Chain
Remember the NADH?
Glycolysis
Kreb’s cycle
PGAL
8 NADH
2 FADH2
4 NADH
Electron Transport Chain
• NADH passes electrons to ETC
• H cleaved off NADH & FADH2
• electrons stripped from H
atoms  H+ (H ions)
• electrons passed from one
electron carrier to next in
mitochondrial membrane (ETC)
• transport proteins in
membrane pump H+ across
inner membrane to
intermembrane space
But what “pulls” the
electrons down the ETC?
Electrons flow downhill
• Electrons move in steps from
carrier to carrier downhill to O2
• each carrier more electronegative
• controlled oxidation
• controlled release of energy
Why the build up
+
H?
• ATP synthase
• enzyme in inner membrane of mitochondria
ADP + Pi  ATP
• only channel permeable to H+
• H+ flow down concentration gradient = provides
energy for ATP synthesis
• molecular power generator!
• flow like water over water wheel
• flowing H+ cause change in shape of ATP
synthase enzyme
• powers bonding of Pi to ADP
• “proton-motive” force
ATP synthesis
• Chemiosmosis couples ETC to ATP synthesis
• build up of H+ gradient just so H+ could flow
through ATP synthase enzyme to build ATP
Peter Mitchell
1961 | 1978
• Proposed chemiosmotic hypothesis
• revolutionary idea at the time
proton motive force
1920-1992
Cellular respiration
Summary of cellular respiration
C6H12O6 + 6O2
•
•
•
•
•
•
 6CO2 + 6H2O + ~36 ATP
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
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?
Taking it beyond…
• What is the final electron acceptor in electron
transport chain?
O2
 So what happens if O2 unavailable?
 ETC backs up
 ATP production ceases
 cells run out of energy
 and you die!
What’s the point?
ATP
The Point is to Make ATP!
Any Questions??