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2006-2007
Cellular RespirationHarvesting Chemical Energy
ATP
Harvesting stored energy Glucose is the model
catabolism of glucose to produce ATP
C6H12O6 6O2 ATP 6H2O 6CO2+ + +
CO2 + H2O + heatfuel
(carbohydrates)
COMBUSTION = making a lot of heat energy by burning fuels in one step
RESPIRATION = making ATP (& some heat)by burning fuels in many small steps
CO2 + H2O + ATP (+ heat)
ATPglucose
glucose + oxygen energy + water + carbondioxide
res
pir
ati
on
O2 O2
+ heat
enzymesATP
How do we harvest energy from fuels? Digest large molecules into smaller ones
break bonds & move electrons from one molecule to another as electrons move they “carry energy” with them that energy is stored in another bond,
released as heat or harvested to make ATP
e-
+ +e-
+ –loses e- gains e- oxidized reduced
oxidation reduction
redox
e-
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 move H = move electrons
pe
+
H
+H
+ –loses e- gains e- oxidized reduced
oxidation reduction
C6H12O6 6O2 6CO2 6H2O ATP+ + +
oxidation
reductionHe-
Coupling oxidation & reduction REDOX reactions in respiration
strip off electrons from C-H bonds by removing H atoms C6H12O6 CO2 = the fuel has been oxidized
electrons attracted to more electronegative atoms
in biology, the most electronegative atom? O2 H2O = oxygen has been reduced
couple REDOX reactions & use the released energy to synthesize ATP
C6H12O6 6O2 6CO2 6H2O ATP+ + +
oxidation
reduction
O
Energy Transfer Substrate level phosphorylation Oxidative phosphorylation
Substrate Level Phosphyralation ATP is formed directly in an enzyme-
catalyzed reaction Phosphate containing group transfers a
phosphate directly to ADP 30.5 kJ/mol of potential energy is also
transferred
Substrate Level Phosphorylation
1) Occurs in glycolysis & Krebs cycle
2) Energy and phosphate are transferred to ADP using an enzyme, to form ATP.
3) PEP (phosphoenolpyruvate) is oxidized.
4) Whereas ADP is reduced. 5) ATP has gained Free Energy
from PEP. ATP can now do work.
Oxidative Phosphorylation ATP is formed indirectly Involves a number of sequential redox
reactions Oxygen is the final electron acceptor More complex More ATP generated
Moving electrons in respiration Electron carriers move electrons by
shuttling H atoms around NAD+ NADH (reduced) FAD+2 FADH2 (reduced)
+ Hreduction
oxidation
PO–
O–
O
–O
PO–
O–
O
–O
CC
O
NH2
N+
H
adenine
ribose sugar
phosphates
NAD+
nicotinamideVitamin B3niacin
PO–
O–
O
–O
PO–
O–
O
–O
CC
O
NH2
N+
HNADH
carries electrons as a reduced molecule
reducing power!
How efficient!Build once,
use many ways
H
like $$in the bank
Oxidative Phosphorylation, NAD+ Nicotinamide adenine dinucleotide,
NAD+ Coenzyme Vitamin B3 Improvements in energy functions
Increasing NAD+ increases availability of these molecules for metabolism
Found in various meats, peanuts and sunflower seeds
Oxidative Phosphorylation, FADFlavin adenine dinucleotide, FAD
Coenzyme Built from riboflavin
Vitamin B2 Found in meats (liver, kidney & heart),
almonds, mushrooms, soybean, green leafy vegetables
Also reduced by two hydrogen atoms Reduced form FADH2
In one reaction of the Krebs cycle
NADH and FADH2 Act as mobile energy carriers Energy harvesting reactions Eventually transfer most of their energy
to ATP molecules
Oxidative Phosphorylation Begins with nicotinamide adenine dinucleotide
(NAD+) Removes 2H atoms from portion of original glucose Electrons are passed from the NADH to
dehydrogenase NADH becomes oxidized
DehydrogenaseDehydrogenase
NADH2
ee ee
NAD+
Oxidative Phosphorylation Occurs in:
One reaction of glycolysis During pyruvate oxidation Three reactions of Krebs cycle
Energy Transfer Goal is to trap energy Substrate level phosphorylation
ATP is formed by enzyme catalyzed reaction 6 ATP made per glucose molecule
Oxidative phosphorylation Many redox reactions form ATP indirectly
More ATP (30) produced per glucose molecule
Forms reduced coenzymes NADH and FADH2 that will eventually transfer their free energy to ATP
Overview of cellular respiration 3 metabolic stages
Anaerobic respiration1. Glycolysis
respiration without O2
in cytosol
Aerobic respiration respiration using O2
in mitochondria
2. Krebs cycle
3. Electron transport chain
C6H12O6 6O2 ATP 6H2O 6CO2+ + + (+ heat)
Glycolysis and Cancer
2007-2008
Cellular RespirationStage 1:
Glycolysis
Glycolysis
glucose pyruvate2x6C 3C
In thecytosol?
Why doesthat make
evolutionarysense?
That’s not enoughATP for me!
Breaking down glucose “glyco – lysis” (splitting sugar)
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
Evolutionary perspective Prokaryotes
first cells had no organelles 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 ALL cells still utilize glycolysis
You meanwe’re related?
Do I have to invitethem over for the holidays?
Enzymesof glycolysis are“well-conserved”
10 reactions convert
glucose (6C) to 2 pyruvate (3C)
produces: 4 ATP & 2 NADH
consumes:2 ATP
net yield: 2 ATP & 2 NADH
glucoseC-C-C-C-C-C
fructose-1,6bPP-C-C-C-C-C-C-P
DHAPP-C-C-C
G3PC-C-C-P
pyruvateC-C-C
Overview
DHAP = dihydroxyacetone phosphateG3P = glyceraldehyde-3-phosphate
ATP2
ADP2
ATP4
ADP4
NAD+2
2Pi
enzyme
enzyme
enzyme enzyme
enzyme
enzyme
enzyme
enzyme
2Pi
2H2
DEMO
Pi
3
6
4,5
ADP
NAD+
Glucose
hexokinase
phosphoglucoseisomerase
phosphofructokinase
Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetonephosphate
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
isomerase
glyceraldehyde3-phosphate
dehydrogenase
aldolase
1,3-Bisphosphoglycerate(BPG)
1,3-Bisphosphoglycerate
(BPG)
1
2
ATP
ADP
ATP
NADH
NAD+
NADH
Pi
CH2
C O
CH2OH
P O
CH2 O P
O
CHOH
C
CH2 O P
O
CHOH
CH2 O PO
CH2OP
O
PO
CH2
H
CH2OHO
CH2 POO
CH2OH
P O
1st half of glycolysis (5 reactions)
Glucose “priming”
get glucose ready to split
split destabilized glucose
2nd half of glycolysis (5 reactions)
Payola!Finally some
ATP!
7
8
H2O9
10
ADP
ATP
3-Phosphoglycerate(3PG)
3-Phosphoglycerate(3PG)
2-Phosphoglycerate(2PG)
2-Phosphoglycerate(2PG)
Phosphoenolpyruvate(PEP)
Phosphoenolpyruvate(PEP)
Pyruvate Pyruvate
phosphoglyceratekinase
phosphoglycero-mutase
enolase
pyruvate kinase
ADP
ATP
ADP
ATP
ADP
ATP
H2O
CH2OH
CH3
CH2
O-
O
C
PH
CHOH
O-
O-
O-
C
C
C
C
C
C
P
P
O
O
O
O
O
O
CH2
NAD+
NADH
NAD+
NADH
Energy Harvest G3P
C-C-C-PPiPi 6
DHAPP-C-C-C
NADH production
ATP production G3P pyruvate
Regulation of Glycolysis and Cancer
Glycolysis summary
net yield
4 ATP
ENERGY INVESTMENT
ENERGY PAYOFF
G3PC-C-C-P
NET YIELD
like $$in the bank
-2 ATP
Substrate-level Phosphorylation
I get it!The Pi camedirectly from
the substrate!
H2O9
10
Phosphoenolpyruvate(PEP)
Phosphoenolpyruvate(PEP)
Pyruvate Pyruvate
enolase
pyruvate kinaseADP
ATP
ADP
ATP
H2O
CH3
O-
O
C
O-
C
C
C
P
O
O
O
CH2
In the last steps of glycolysis, where did the P come from to make ATP?
ATP
Energy accounting of glycolysis
Net gain = some energy investment (-2 ATP) small energy return (4 ATP + 2 NADH)
1 6C sugar
glucose pyruvate2x6C 3C
All that work! And that’s all
I get?
Butglucose has
so much moreto give!
2006-2007
Cellular RespirationStage 2:
Citric Acid Cycle orKrebs Cycle
pyruvate CO2
Glycolysis is only the start Glycolysis
Pyruvate has more energy to yield
2x6C 3Cglucose pyruvate
3C 1C
Cellular respiration
pyruvate acetyl CoA + CO2
Oxidation of pyruvate
NAD
3C 2C 1C[2x ] releases reduces produces
Citric Acid cycle1937 | 1953
Hans Krebs1900-1981
citrate
acetyl CoACount the carbons!
pyruvate
x2
oxidationof sugars
This happens twice for each glucose molecule
6C
5C
citrate
acetyl CoACount the electron carriers!
pyruvate
reductionof electron
carriers
This happens twice for each glucose molecule x2
CO2
NADH
What’s the point?
Electron Carriers = Hydrogen Carriers
What’s so important about
electron carriers?
H+
H+H+
H+
H+ H+
H+H+H+
ATP
ADP+ Pi
Energy accounting of Citric Acid cycle
Net gain =
1 ADP 1 ATPATP
2x
4 NAD + 1 FAD 4 NADH + 1 FADH2
pyruvate CO2
3C 3x 1C
Value of Citric Acid cycle? If the yield is only 2 ATP then how was the
Citric Acid cycle an adaptation?
like $$in the bank
The Second Law of Thermodynamics states that spontaneous processes tend to increase the entropy (disorder) of the universe. Why would this law favor a glucose molecule being broken down?
The First Law of Thermodynamics states that energy is neither created or destroyed in any process, including chemical reactions. Looking at the big picture of life, and assuming energy used by organisms comes from the sun, how does ATP production by cellular respiration obey the First Law?