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Cellular Respiration
Stage 1:
Glycolysis
AP Biology
2007-2008
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2007-2008
Glycolysis
 Breaking down glucose

“glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C

In the
cytosol?
Why does
that make
evolutionary
sense?
inefficient
 generate only 2 ATP for every 1 glucose

occurs in cytosol
AP Biology
That’s not enough
ATP for me!
Evolutionary perspective
 Prokaryotes are ancestors of all modern
life
 no organelles (no mitochonria)
 Anaerobic atmosphere
No free oxygen (O2) in atmosphere
 ALL cells still utilize glycolysis

AP Biology
Overview
glucose
C-C-C-C-C-C
10 reactions
enzyme
2 ATP
enzyme
2 ADP
convert
fructose-1,6bP
glucose (6C) to
P-C-C-C-C-C-C-P
enzyme
enzyme
2 pyruvate (3C)
enzyme
 produces:
4 ATP & 2 NADH P-C-C-C C-C-C-P
2H
 consumes:
2Pi enzyme
2 ATP
enzyme
 net yield:
2Pi
enzyme
2 ATP & 2 NADH

DHAP = dihydroxyacetone phosphate
AP Biology
G3P
= glyceraldehyde-3-phosphate
pyruvate
C-C-C
2 NAD+
2
4 ADP
4 ATP
Glycolysis summary
endergonic
invest some ATP
ENERGY INVESTMENT
-2 ATP
ENERGY PAYOFF
G3P
C-C-C-P
4 ATP
NET YIELD
AP Biology
exergonic
harvest a little
ATP & a little NADH
net yield
2 ATP
2 NADH
 http://www.youtube.com/watch?v=3GTj
QTqUuOw&feature=related
 http://highered.mcgrawhill.com/sites/007352543x/student_view
0/chapter8/how_glycolysis_works.html
AP Biology
1st half of glycolysis (5 reactions)
Glucose “priming”

get glucose ready
to split
 phosphorylate
CH2 O
O
P
Glucose 6-phosphate
2
P O
ADP
CH2 O
O
P
CH2
CH2
CH2OH
O
Fructose 1,6-bisphosphate
O CH2
C
4,5 aldolase
isomerase
O Dihydroxyacetone
CH2OH phosphate
Glyceraldehyde 3
-phosphate (G3P)
Pi
NAD+
Pi
6
glyceraldehyde
NADH
NADH
3-phosphate
P
dehydrogenase
1,3-Bisphosphoglycerate 1,3-Bisphosphoglycerate
(BPG)
(BPG)
H
C
O
CHOH
CH2 O
NAD+
AP Biology
O
Fructose 6-phosphate
3
ATP
phosphofructokinase
split destabilized
glucose
P
ADP
phosphoglucose
isomerase
glucose
 molecular
rearrangement

CH2OH
Glucose
1
ATP
hexokinase
O
P
O
CHOH
CH2 O
P
O
P
Important enzyme
Phosphofructokinase (PFK) in
step “3” of glycolysis (second ATP is
used) (Allosteric enzyme)
Activated by ADP (speeds
respiration when ATP is needed)
Inhibited by ATP (slows respiration
when ATP is in excess)
AP Biology
2nd half of glycolysis (5 reactions)
DHAP
P-C-C-C
Energy Harvest

NADH production
 G3P donates H
 NAD+  NADH

ATP production
 G3P    pyruvate
 PEP sugar donates P
 “substrate level
phosphorylation”
 ADP  ATP
NAD+
Pi
G3P
C-C-C-P
Pi
6
NAD+
NADH
NADH
7
phosphoglycerate
kinase
ADP
ATP
3-Phosphoglycerate
(3PG)
ADP
ATP
3-Phosphoglycerate
(3PG)
8
phosphoglyceromutase
2-Phosphoglycerate
(2PG)
Phosphoenolpyruvate
(PEP)
ADP
H2O
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
ADP
C O
H C O
CH2OH
Pyruvate
C
C
O
O
CH2
OC
ATP
Pyruvate
O P
P
O-
ATP
AP Biology
CHOH
CH2
O-
2-Phosphoglycerate
(2PG)
9
enolase
H2O
OC
O
C O
CH3
P
Substrate-level Phosphorylation



ATP is made directly from a “substrate”
The Substrate is phosphorylated, oxidized
and ATP is made from ADP
The 4 ATP made in Glycolysis are made
this way
ATP
9
enolase
H2O
Phosphoenolpyruvate
(PEP)
ADP
OH2O
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
ATP
ATP
Pyruvate
AP Biology
I get it!
The Pi came
directly from
the substrate!
ADP
Pyruvate
C
C
CH2
O
O
OC
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
But
glucose has
so much more
to give!
 Net gain = 2 ATP + 2 NADH
 1 6C sugar  2 3C sugars- (pyruvates)
AP Biology
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
AP Biology
O2
glucose     pyruvate
2x 3C
6C
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
anaerobic
respiration
mitochondria
Krebs cycle
aerobic respiration
AP Biology
Lactic Acid Fermentation(anaerobic)
 C3H4O3
Pyruvate
NADH
C3H6O3
NAD+
Lactate
Pyruvate is REDUCED to Lactate and NAD+
is regenerated so respiration can
continue.
This occurs in muscles in O2 debt (when
running hard) until the debt is repaid
(when you slow down)
AP Biology
 There is no O2. Therefore pyruvate
cannot be oxidized. Instead, it is
reduced by NADH. No more ATP can be
made
AP Biology
Alcohol Fermentation
pyruvate  ethanol + CO2
3C
NADH
2C
NAD+
 Dead end process
 at ~12% ethanol,
kills yeast
AP Biology
1C
bacteria
yeast
recycle
NADH
Lactic Acid Fermentation
pyruvate  lactic acid

3C
NADH
3C
NAD+
 Reversible process
 once O2 is available,
lactate is converted
back to pyruvate by
the liver
Count the
carbons!
AP Biology
O2
animals
some fungi
recycle
NADH
Fermentation (anaerobic)
 Bacteria, yeast
pyruvate  ethanol + CO2
3C
2C
NADH
1C
NAD+
 beer, wine, bread
 Pyruvate is reduced to ethanol
 Animals, some fungi
pyruvate  lactic acid
3C
NADH
3C
NAD+
 anaerobic exercise (no O2)
AP Biology
 Pyruvate is reduced to lactate