Chapter 9. Cellular Respiration STAGE 1: Glycolysis

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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?
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

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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

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ALL cells still utilize glycolysis
You mean
we’re related?
Do I have to invite
them over for
the holidays?
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
DHAP
G3P
 produces:
4 ATP & 2 NADH P-C-C-C C-C-C-P
2H
 consumes:
2Pi enzyme
2 ATP
enzyme
 net:
2Pi
enzyme
2 ATP & 2 NADH

DHAP = dihydroxyacetone phosphate
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G3P
= glyceraldehyde-3-phosphate
pyruvate
C-C-C
2 NAD+
2
4 ADP
4 ATP
Glycolysis summary
endergonic
invest some ATP
ENERGY INVESTMENT
ENERGY PAYOFF
G3P
C-C-C-P
4ATP
exergonic
harvest a little
ATP & a little NADH
like $$
in the
bank
NET YIELD
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yield
2 ATP
2 NADH
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+
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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
2nd half of glycolysis (5 reactions)
G3P
C-C-C-P
Energy Harvest
NAD+

NADH production
ADP
 oxidize sugar
ATP


NAD+
Pi
6
NAD+
NADH
 G3P donates H
 reduce NAD+
Pi
NADH
7
phosphoglycerate
kinase
3-Phosphoglycerate
(3PG)
 NADH
ADP
ATP
3-Phosphoglycerate
(3PG)
8
phosphoglyceromutase
 G3P  pyruvate
 PEP sugar donates P
 ADP  ATP
Phosphoenolpyruvate
(PEP)
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Payola!
Finally some
ATP!
ADP
2-Phosphoglycerate
(2PG)
9
enolase
H2O
O P
C O
H C O
CH2OH
P
OH2O
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
ADP
ATP
Pyruvate
C
C
O
O
CH2
OC
ATP
Pyruvate
CHOH
CH2
O-
ATP production
2-Phosphoglycerate
(2PG)
OC
O
C O
CH3
P
Substrate-level Phosphorylation
 In the last steps of glycolysis, where did
the P come from to make ATP?

9
the sugar substrateH O(PEP) enolase
OH2O
2
P is transferred
from PEP to ADP
 kinase enzyme
 ADP  ATP
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Phosphoenolpyruvate
(PEP)
ADP
Phosphoenolpyruvate
(PEP)
10
pyruvate kinase
Pyruvate
I get it!
The PO4 came
directly from
the substrate!
Pyruvate
C
CH2
O
O
OC
ATP
ATP
ATP
ADP
C
O
C O
CH3
P
Energy accounting of glycolysis
2 ATP
2 ADP
glucose      pyruvate
2x 3C
6C
4 ADP
4 ATP
 Net gain = 2 ATP


some energy investment (-2 ATP)
small energy return (+4 ATP)
 1 6C sugar  2 3C sugars
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All that work!
And that’s all
I get?
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
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O2
glucose     pyruvate
2x 3C
6C
Hard way
to make
a living!
We can’t stop there!
G3P
DHAP
NAD+
Pi
NAD+
Pi
NADH
NADH
1,3-BPG
1,3-BPG
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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
recycle
NADH
How is NADH recycled to NAD+?
Another molecule
must accept H
from NADH
H2O
O2
recycle
NADH
with oxygen
without oxygen
aerobic respiration
anaerobic respiration
fermentation
pyruvate
NAD+
NADH
acetyl-CoA
CO2
NADH
NAD+
lactate
acetaldehyde
NADH
NAD+
(lactic acid)
which path you
use depends on
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who
you are…
Krebs
cycle
ethanol
Fermentation (anaerobic)
 Bacteria, yeast
pyruvate  ethanol + CO2
3C
NADH
2C
1C
NAD+
 beer, wine, bread
to glycolysis
 Animals, some fungi
pyruvate  lactic acid
3C
NADH

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3C
NAD+to glycolysis
cheese, anaerobic exercise (no O2)
Alcohol Fermentation
pyruvate  ethanol + CO2
3C
NADH
2C
NAD+
 Dead end process
 at ~12% ethanol,
kills yeast
 can’t reverse the
reaction
Count the
carbons!
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1C
bacteria
yeast
animals
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!
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O2
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
anaerobic
respiration
mitochondria
Kreb’s cycle
aerobic respiration
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What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2007-2008
H+
And how do we do that? H
+
H+
H+
H+
H+
H+
H+
 ATP synthase
set up a H+ gradient
 allow H+ to flow
through ATP synthase
 powers bonding
of Pi to ADP

ADP + P
ADP + Pi  ATP
ATP
H+
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But…
Have we done that yet?
NO!
There’s still more
to my story!
Any Questions?
AP Biology
2007-2008

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