Chapter 9.
Cellular Respiration
STAGE 1: Glycolysis
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What’s the point?
ATP
The Point is to Make ATP!
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2005-2006
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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?
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Why does it make sense that this happens in the cytosol?
Who evolved first?
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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
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You mean,
I’m related
to them?!
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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
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glucose
C-C-C-C-C-C
Overview
 10 reactions
convert
6C glucose to
two 3C pyruvate
 produce 2 ATP
& 2 NADH
ac
tiv
e n a tio
e rg n
y
2 ATP
2 ADP

fructose-6P
P-C-C-C-C-C-C-P
DHAP
P-C-C-C
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PGAL
C-C-C-P
pyruvate
C-C-C
2 NAD+
2 NADH
4 ADP
4 ATP
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1st ATP used is like a match to light a fire…
initiation energy / activation energy.
Destabilizes glucose enough to split it in two
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Glycolysis summary
endergonic
invest some ATP
exergonic
harvest a little
more ATP
& a little NADH
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2005-2006
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.
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1st half of glycolysis (5 reactions)
 Glucose
“priming”

get glucose
ready to split
 phosphorylate
glucose
 rearrangement

split
destabilized
glucose
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Pay
attention to
the enzymes!
PGAL
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2nd half of glycolysis (5 reactions)
 Oxidation
G3P donates H
 NAD → NADH

 ATP generation
G3P → pyruvate
 donates P
 ADP → ATP

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Payola!
Finally some
ATP!
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OVERVIEW OF GLYCOLYSIS
1
6-carbon glucose
(Starting material)
2 ATP
P
P
6-carbon sugar diphosphate
2
3
P
P
6-carbon sugar diphosphate
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
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.
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Cleavage reactions. Then, the
six-carbon molecule with two
phosphates is split in two, forming
two three-carbon sugar
phosphates.
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
NADH
2 ATP
2 ATP
3-carbon
pyruvate
3-carbon
pyruvate
Energy-harvesting reactions.
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.
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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
I get it!
The P came
directly from
the substrate!
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Energy accounting of glycolysis
2 ATP
2 ADP
glucose → → → → → pyruvate
2x 3C
6C
4 ADP
4 ATP
 Net gain = 2 ATP


All that
work! And
that’s all I
get?
some energy investment (2 ATP)
small energy return (4 ATP)
 1 6C sugar → 2 3C sugars
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And that’s how life subsisted for a billion years.
Until a certain bacteria ”learned” how to metabolize O2; which was
previously a poison.
But now pyruvate is not the end of the process
 Pyruvate still has a lot of energy in it that has not been
captured.
 It still has 3 carbons bonded together!
There is still energy stored in those bonds.
It can still be oxidized further.
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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
 only harvest 3.5% of energy stored in glucose
 slow growth, slow reproduction
Heck of a
way to make
a living!
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So why does glycolysis still take place?
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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
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How is NADH recycled to NAD+?
 Another molecule must accept H from NADH

aerobic respiration
 ethanol fermentation
 lactic acid fermentation

aerobic respiration
NADH
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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 O22005-2006
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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.
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Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
Kreb’s cycle
mitochondria
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What’s the point?
ATP
The Point is to Make ATP!
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Any Questions??
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