Cellular Respiration

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Transcript Cellular Respiration

Making energy!
ATP
The point
is to make
ATP!
Chemical
energy
First Law
Of Thermodynamics
(a)
First law of thermodynamics: Energy
can be transferred or transformed but
Neither created nor destroyed. For
example, the chemical (potential) energy
in food will be converted to the kinetic
energy of the cheetah’s movement in (b).
Figure 8.3
Heat
Second Law
co2
+
H2O
(b)
Second law of thermodynamics: Every energy transfer or transformation increases
the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s
surroundings in the form of heat and the small molecules that are the by-products
of metabolism.
Figure 8.3
Free Energy
Reactions in a Closed System:
∆G < 0
∆G = 0
What would happen
To a living
System if it were closed?
Body Cells:
∆G < 0
What do we
Need to
Stay alive?
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
digestion
+
synthesis
+
+
energy
+
energy
ATP
 Adenosine TriPhosphate

modified nucleotide
 nucleotide =
adenine + ribose + Pi  AMP
 AMP + Pi  ADP
 ADP + Pi  ATP
 adding phosphates is endergonic
How efficient!
Build once,
use many ways
high energy bonds
How does ATP store energy?
ADP
AMP
ATP
I think
he’s a bit
unstable…
don’t you?
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
Instability of its P bonds makes ATP an excellent energy donor
How does ATP transfer energy?
ADP
ATP
O– O– O –
–O P –O
O– P –O
O– P O–
O O O
O–
–O P O – +
O
7.3
energy
 ATP  ADP

releases energy
 ∆G = -7.3 kcal/mole
 Fuel other reactions
 Phosphorylation

released Pi can transfer to other molecules
 destabilizing the other molecules

enzyme that phosphorylates = “kinase”
An example of Phosphorylation…
 Building polymers from monomers
need to destabilize the monomers
 phosphorylate!

H
C
OH
+
H
C
HO
H
C It’s
never that
OH
simple!
+ ATP
H
C
+
P
H
C
HO
synthesis
+4.2 kcal/mol
“kinase”
enzyme
-7.3 kcal/mol
-3.1 kcal/mol
enzyme
H H
C C
O
H
C
H H
C C
OHHO
+
+
H2O
ADP
P
H H
C C
O
+
Pi
Cells spend a lot of time making ATP!
The
point is to make
ATP!
What’s the
point?
How is ATP Made in a Cell?
Substrate Level
Phosphorylation
Chemiosmosis
Start with a mitochondrion or
chloroplast
Trap H+ in the
intermembrane space
Chemiosmosis
Start with a mitochondrion or
chloroplast
Trap H+ in the
intermembrane space
How can this
lead to
ATP production?
H+
ATP synthase
 Enzyme channel in
H+
H+
H+
H+
H+
H+
H+
rotor
mitochondrial membrane


permeable to H+
H+ flow down
concentration gradient
rod
 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?
catalytic
head
H+
That’s the rest
of my story!
Any Questions?
Cellular Respiration
Harvesting Chemical Energy
ATP
What’s the
point?
The point
is to make
ATP!
ATP
Harvesting stored energy
 Energy is stored in organic molecules
carbohydrates, fats, proteins
Heterotrophs eat these organic molecules  food


Which
releases more
Energy, combustion
Of glucose or
Cellular respiration?
respiration
Harvesting stored energy
glucose + oxygen  energy + water + carbon
dioxide
C6H12O6 +
6O2
 ATP + 6H2O + 6CO2 + heat
COMBUSTION = making a lot of heat energy
by burning fuels in one step
fuel
carbohydrates)
RESPIRATION = making ATP (& some heat)
by burning fuels in many small steps
ATP
enzymes
O2
ATP
O2
CO2 + H2O + ATP (+ heat)
glucose
CO2 + H2O + heat
How do we harvest energy from fuels?
 Oxidation Reduction
loses e-
gains e-
+
oxidized
reduced
+
+
eoxidation
e-
–
ereduction
redox
How do we move electrons in biology?
 Moving electrons in living systems

electrons cannot move alone in cells
 electrons move as part of H atom
e
p
 move H = move electrons
loses e-
gains e-
oxidized
+
+
oxidation
reduced
+
–
H
reduction
H
oxidation
C6H12O6 +
H e-
6O2
 6CO2 + 6H2O + ATP
reduction
like $$
in the bank
Moving electrons in respiration
 Electron carriers move mighty electrons by
shuttling H atoms around
 NAD+  NADH (reduced)
 FAD+2  FADH2 (reduced)
NAD+
nicotinamide
Vitamin B3
niacin
O–
O – P –O
O
phosphates
O–
O – P –O
O
H
reducing power!
NADH
O
H H
C NH2
N+
+
adenine
ribose sugar
C NH2
reduction
O–
–
–
oxidation O P O
O
O–
O – P –O
O
carries electrons as
H
O
a reduced molecule
N+
How efficient!
Build once,
use many ways
Overview of cellular respiration
 4 metabolic stages

Anaerobic respiration
1. Glycolysis
 respiration without O2
 in cytosol

Aerobic respiration
 respiration using O2
 in mitochondria
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain
C6H12O6 +
6O2
 ATP + 6H2O + 6CO2 (+ heat)
Cellular Respiration
Stage 1:
Glycolysis
Glycolysis
 Breaking down glucose

“glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C

In the
cytosol?
Why does
that make
evolutionary
sense?
but it’s inefficient
 generate only 2 ATP for every 1
glucose
 still is starting point for ALL cellular
respiration

occurs in cytosol
That’s not
enough
ATP for me
QuickTime™ and a
decompressor
are needed to see this picture.
Evolutionary perspective
Enzymes
of glycolysis are
“well-conserved”
 Prokaryotes

first cells had no organelles
 Anaerobic atmosphere

life on Earth first evolved without free oxygen (O2)
in atmosphere
 Prokaryotes that evolved glycolysis are ancestors
of all modern life

ALL cells still utilize glycolysis
You mean
we’re related?
Do I have to invite
them over for
the holidays?
Overview
glucose
C-C-C-C-C-C
10 reactions
enzyme
2 ATP
enzyme
2 ADP
fructose-1,6bP
P-C-C-C-C-C-C-P
enzyme
enzyme
enzyme
What has more
Free energy,
G3P or pyruvate?
DHAP
P-C-C-C
G3P
C-C-C-P
2H
2Pi enzyme
2 NAD+
2
enzyme
2Pi
4 ADP
enzyme
pyruvate
C-C-C
4 ATP
Glycolysis summary
endergonic
invest some ATP
ENERGY INVESTMENT
-2 ATP
ENERGY PAYOFF
G3P
C-C-C-P
4 ATP
exergonic
harvest a little
ATP & a little NADH
like $$
in the
bank
NET YIELD
net yield
2 ATP
2 NADH
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
Phosphoenolpyruvate
(PEP)
ADP
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
Pyruvate
What sort of
Enzyme does
This?
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


some energy investment (-2 ATP)
small energy return (4 ATP + 2 NADH)
 1 6C sugar  2 3C sugars
The
magic number
is?
Where is the
Extra energy?
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
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
6
1,3-BPG
NAD+
Pi
+
NADH
NAD
1,3-BPG
NADH
7
ADP
Glycolysis
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+
What is the
 without
regenerating NAD+,
Oxidizing
Agent of
energyGlycolysis?
production would stop!

9
H2O
H2O
Phosphoenolpyruvate
(PEP)
another molecule must accept HADP
from NADH
ATP
 so NAD+ is freed up for another round
Phosphoenolpyruvate
(PEP)
10
ADP
ATP
Pyruvate
Pyruvate
How is NADH recycled to NAD+?
without oxygen
with oxygen
Another molecule
aerobic respiration
must accept the
mighty electrons from pyruvate
NADH
NAD+
HO
anaerobic respiration
“fermentation”
CO2
2
recycle
NADH
O2
NADH
acetyl-CoA
NADH
NAD+
lactate
What has more
Free energy
Pyruvate or
Lactic acid?
acetaldehyde
NADH
NAD+
lactic acid
fermentation
Krebs
cycle
ethanol
alcohol
fermentation
Fermentation (anaerobic)
 Bacteria, yeast
pyruvate  ethanol + CO2
3C
NADH
2C
NAD+
 beer, wine, bread
1C
back to glycolysis
 Animals, some fungi
pyruvate  lactic acid
3C
NADH
3C
NAD+back to glycolysis
 cheese, anaerobic exercise (no O2)
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
anaerobic
respiration
mitochondria
Krebs cycle
aerobic respiration
What’s the
point?
The point
is to make
ATP!
ATP
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
]
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  mitochondria)
Count the carbons!
pyruvate
3C
2C
6C
4C
This happens
twice for each
glucose
molecule
4C
acetyl CoA
citrate
oxidation
of sugars
CO2
x2
4C
4C
6C
5C
4C
CO2
Count the electron carriers!
pyruvate
3C
6C
4C
NADH
This happens
twice for each
glucose
molecule
2C
4C
4C
acetyl CoA
citrate
reduction
of electron
carriers
x2
FADH2
4C ATP
CO2
NADH
6C
CO2
NADH
5C
4C
CO2
NADH
Whassup?
So we fully
oxidized
glucose
C6H12O6

CO2
& ended up
with 4 ATP!
What’s the
point?
Electron Carriers = Hydrogen Carriers
H+
 Krebs cycle
produces large
quantities of
electron carriers
NADH
 FADH2
 go to Electron
Transport Chain!

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
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
What’s the
point?
The point
is to make
ATP!
ATP
Where is all of the energy after
glycolysis and citric acid cycle?
 It is in the 4 ATP’s that were made
 But where is the rest of the energy?
 It is in the NADH and FADH2’s
Time to
break open
the piggybank!
Where can these
Electrons go?
So far the ATP’s have been generated via substrate level
phosphorylation
Now it’s time
for
chemiosmosis
Where is the
energy
Coming from
for the
active transport?
???
What pulls electrons
out of the chain?
What happens to the
energy that is lost from
the electrons?
AHH, the
active
transport!
QuickTime™ and a
decompressor
are needed to see this picture.
Peter Mitchell
1961 | 1978
 Proposed chemiosmotic hypothesis

revolutionary idea at the time
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
H+
ATP
ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
H+
ATP
synthase
How are 34
ATPs made
Variables in ATP yield:
 Some mitochondria differ in permeability to



protons, which effects the proton motive
force.
Proton motive force may be directed to drive
other cellular processes such as active
transport.
ATP yield is inflated by rounding up
Prokaryotic cellular respiration is slightly
higher since no mitochondrial membrane
used to transport electrons from NADH.
How do we
use food other
than glucose
to generate
energy?