Chapter 9. Cellular Respiration STAGE 1: Glycolysis

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Cellular Respiration Stage 1 Glycolysis
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Whats thepoint?
The pointis to makeATP!
ATP
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Glycolysis

• 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 its inefficient
• generate only 2 ATP for every 1 glucose
• occurs in cytosol

In thecytosol?Why doesthat makeevolutionaryse
nse?
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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 meanwere related?Do I have to invitethem
over for the holidays?
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Overview
glucose C-C-C-C-C-C

• 10 reactions
• convert glucose (6C) to 2 pyruvate (3C)
• produces 4 ATP 2 NADH
• consumes2 ATP
• net 2 ATP 2 NADH

fructose-1,6bP P-C-C-C-C-C-C-P
DHAP P-C-C-C
G3P C-C-C-P
pyruvate C-C-C
DHAP dihydroxyacetone phosphate G3P
glyceraldehyde-3-phosphate
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Glycolysis summary
endergonic invest some ATP
ENERGY INVESTMENT
G3P C-C-C-P
exergonic harvest a little ATP a little NADH
ENERGY PAYOFF
4ATP
like in the bank
yield 2 ATP 2 NADH
NET YIELD
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1st half of glycolysis (5 reactions)
CH2OH
Glucose priming
O
Glucose
1
ATP
hexokinase

• get glucose ready to split
• phosphorylate glucose
• molecular rearrangement
• split destabilized glucose

ADP
CH2
P
O
O
Glucose 6-phosphate
2
phosphoglucose isomerase
CH2
P
O
CH2OH
O
Fructose 6-phosphate
3
ATP
phosphofructokinase
CH2
O
P
CH2
O
P
O
ADP
Fructose 1,6-bisphosphate
aldolase
4,5
H
CH2
O
isomerase
P
C
O
C
O
Glyceraldehyde 3 -phosphate (G3P)
Dihydroxyacetone phosphate
CHOH
CH2OH
CH2
O
P
Pi
NAD
NAD
Pi
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glyceraldehyde 3-phosphate dehydrogenase
NADH
NADH
P
O
O
CHOH
1,3-Bisphosphoglycerate (BPG)
1,3-Bisphosphoglycerate (BPG)
CH2
O
P
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2nd half of glycolysis (5 reactions)
G3P C-C-C-P
Energy Harvest

• NADH production
• G3P donates H
• oxidize sugar
• reduce NAD
• NAD ? NADH
• ATP production
• G3P ? pyruvate
• PEP sugar donates P
• ADP ? ATP

Pi
NAD
NAD
Pi
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NADH
NADH
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ADP
ADP
O-
phosphoglycerate kinase
C
ATP
ATP
CHOH
3-Phosphoglycerate (3PG)
3-Phosphoglycerate (3PG)
CH2
P
O
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O-
phosphoglyceromutase
O
C
P
H
C
O
2-Phosphoglycerate (2PG)
2-Phosphoglycerate (2PG)
CH2OH
O-
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H2O
H2O
enolase
C
O
O
C
P
Phosphoenolpyruvate (PEP)
Phosphoenolpyruvate (PEP)
CH2
O-
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ADP
ADP
C
O
Payola!Finally some ATP!
pyruvate kinase
ATP
ATP
O
C
CH3
Pyruvate
Pyruvate
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Substrate-level Phosphorylation

• In the last steps of glycolysis, where did the P
  come from to make ATP?
• the sugar substrate (PEP)

• P is transferred from PEP to ADP
• kinase enzyme
• ADP ? ATP

ATP
I get it! The PO4 camedirectly fromthe
substrate!
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Energy accounting of glycolysis
glucose ? ? ? ? ? pyruvate
6C
3C
2x
All that work! And thats all I get?

• Net gain 2 ATP
• some energy investment (-2 ATP)
• small energy return (4 ATP)
• 1 6C sugar ? 2 3C sugars

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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

glucose ? ? ? ? pyruvate
6C
Hard wayto makea living!
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We cant stop there!
Glycolysis glucose 2ADP 2Pi 2 NAD ? 2
pyruvate 2ATP 2NADH

• Going to run out of NAD
• without regenerating NAD, energy production
  would stop!
• another molecule must accept H from NADH

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How is NADH recycled to NAD?
with oxygen aerobic respiration
without oxygen anaerobic respiration fermentation

• Another molecule must accept H from NADH

pyruvate
NAD
H2O
CO2
NADH
NADH
O2
acetaldehyde
NADH
acetyl-CoA
NAD
NAD
lactate
(lactic acid)
which path you use depends on who you are
Krebs cycle
ethanol
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Fermentation (anaerobic)

• Bacteria, yeast

to glycolysis??

• beer, wine, bread

• Animals, some fungi

to glycolysis??

• cheese, anaerobic exercise (no O2)

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Alcohol Fermentation
bacteria yeast

• Dead end process
• at 12 ethanol, kills yeast
• cant reverse the reaction

Count thecarbons!
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Lactic Acid Fermentation
animals
?

• Reversible process
• once O2 is available, lactate is converted back
  to pyruvate by the liver

Count thecarbons!
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Pyruvate is a branching point

• Pyruvate

fermentation anaerobicrespiration
mitochondria Krebs cycle aerobic respiration
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Whats thepoint?
The pointis to makeATP!
ATP
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And how do we do that?

• ATP synthase
• set up a H gradient
• allow H to flow through ATP synthase
• powers bonding of Pi to ADP
• ADP Pi ? ATP

ADP
ATP
But Have we done that yet?
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NO!Theres still more to my story! Any Questions?