1. Cellular Respiration Stage 1: Glycolysis

2. glucose      pyruvate
GLYCOLYSIS
Breaking down glucose
“glyco – lysis” (splitting sugar)
What? Starting point for all cell respiration [transfers energy to ATP]
Where? Cytoplasm
Why? generate only 2 ATP for every 1 glucose
inefficient
glucose      pyruvate 2x 6C 3C
Why does it make sense that this happens in the cytosol?
Who evolved first?

3. Evolution Anaerobic atmosphere Prokaryotes first evolved glycolysis
life on Earth first evolved without free oxygen (O2)
Prokaryotes first evolved glycolysis
Ancestors of all modern life
ALL cells still utilize glycolysis
The enzymes of glycolysis are very similar among all organisms. The genes that code for them are highly conserved.
They are a good measure for evolutionary studies. Compare eukaryotes, bacteria & archaea using glycolysis enzymes.
Bacteria = 3.5 billion years ago
glycolysis in cytosol = doesn’t require a membrane-bound organelle
O2 = 2.7 billion years ago
photosynthetic bacteria / proto-blue-green algae
Eukaryotes = 1.5 billion years ago
membrane-bound organelles!
Processes that all life/organisms share:
Protein synthesis
Glycolysis
DNA replication

4. Glycolysis summary 4ATP INVEST  endergonic CLEAVAGE  exergonic
invest some ATP to
break stable glucose
ENERGY INVESTMENT
G3P
C-C-C-P
CLEAVAGE  exergonic
harvest a little ATP &
NADH by splitting
glucose   PGAL/G3P
ENERGY PAYOFF
4ATP
Glucose is a stable molecule it needs an activation energy to break it apart.
phosphorylate it = Pi comes from ATP.
make NADH & put it in the bank for later.
HARVEST
Rearrange PGAL  
Yield is 2 ATP, 2 NADH,
2 pyruvate
NET YIELD

5. Stage 1 of Glycolysis: Investment
Glucose “priming”
rearrange molecules
split glucose into
2 G3P
[PGAL]
Requires 2 ATP to add 2 Phosphates
phosphoglucose
isomerase
CH2 O P O
CH2OH
Fructose 6-phosphate 3
ATP
phosphofructokinase P O
CH2
CH2 O P
ADP O
Fructose 1,6-bisphosphate
aldolase
4,5 H
isomerase C O
Glyceraldehyde 3
-phosphate (G3P)
CHOH

6. Stage 2 of Glycolysis: Energy Harvest
2 PGALS become 2 Pyruvates
2 NADH
NAD+ reduced to NADH
4 ATP produced
2 net Pi Pi
NAD+ 6
NADH 7
ADP O-
phosphoglycerate
kinase
ATP C
CHOH
3-Phosphoglycerate
(3PG)
3-Phosphoglycerate
(3PG)
CH2 O 8 O-
phosphoglyceromutase C O H C O
2-Phosphoglycerate
(2PG)
2-Phosphoglycerate
(2PG)
CH2OH 9 O-
H2O
enolase
H2O C O C O
Phosphoenolpyruvate
(PEP)
Phosphoenolpyruvate
(PEP)
CH2 O-
ADP 10
ADP
pyruvate kinase C O
ATP
ATP C O
Pyruvate
Pyruvate
CH3

7. Substrate-level Phosphorylation
where did the P come from to make ATP?
From sugar substrate [G3P/PGAL]
H2O 9 10
Phosphoenolpyruvate
(PEP)
Pyruvate
enolase
pyruvate kinase
ADP
ATP
CH3 O- O C P
CH2
P is transferred from PGAL to ADP
kinase enzyme
ADP  ATP
ATP

8. Pi
NAD+
G3P
1,3-BPG
NADH
DHAP
Glycolysis
glucose + 2ADP + 2Pi + 2 NAD+  2 pyruvate + 2ATP + 2NADH
Need NAD+
Without regenerating NAD+, energy production would stop!
Must continue after glycolysis
The molecule that accepts the H+ is Oxygen

9. Another molecule must accept H from NADH (oxygen)
with oxygen
aerobic respiration
without oxygen
anaerobic respiration
fermentation
pyruvate
H2O
NAD+
CO2
NADH O2
NADH
acetaldehyde
acetyl-CoA
NADH
NAD+
NAD+
lactate
(lactic acid)
which path you use depends on who you are…
Krebs
cycle
ethanol

10. Fermentation (anaerobic)
Bacteria, yeast 1C 3C 2C
pyruvate  ethanol + CO2
NADH
NAD+
to glycolysis
beer, wine, bread
Animals, some fungi
Count the carbons!!
Lactic acid is not a dead end like ethanol. Once you have O2 again, lactate is converted back to pyruvate by the liver and fed to the Kreb’s cycle.
pyruvate  lactic acid 3C
NADH
NAD+
to glycolysis
cheese, anaerobic exercise (no O2)

11. Alcohol Fermentation pyruvate  ethanol + CO2 Dead end process 1C 3C
bacteria yeast
Alcohol Fermentation 1C 3C 2C
pyruvate  ethanol + CO2
NADH
NAD+
Dead end process
at ~12% ethanol, kills yeast
can’t reverse the reaction

12. Lactic Acid Fermentation
animals
Lactic Acid Fermentation O2
pyruvate  lactic acid 3C 
NADH
NAD+
Reversible
once O2 is available, lactate is converted back to pyruvate by the liver

13. Pyruvate is a branching point
fermentation
anaerobic respiration
mitochondria
Kreb’s cycle
aerobic respiration