Download Chapter 9. Cellular Respiration STAGE 1: Glycolysis

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
Glycolysis
 1. Both types of PATHWAYS BEGIN with Glycolysis.
 2. Glycolysis is a pathway in which One Six-Carbon
Molecule of GLUCOSE is Oxidized to Produce Two ThreeCarbon Molecules of PYRUVIC ACID OR PYRUVATE.
 3. The word "GLYCOLYSIS" means "The Splitting of
Glucose". In a series of Ten Reactions, a molecule of
Glucose is split into Two identical smaller molecules, each
called PYRUVIC ACID or PYRUVATE.
 4. GLYCOLYSIS IS THE PROCESS BY WHICH GLUCOSE IS
CONVERTED TO PYRUVIC ACID, AND SOME OF ITS
ENERGY IS RELEASED.
 5. Glycolysis occurs in the CYTOSOL OF THE CELL.
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GLYCOLYSIS
 6. Whether or not Oxygen is present, Glycolysis
SPLITS (BY OXIDATION) GLUCOSE INTO THREECARBON MOLECULES OF PGAL. PGAL IS THEN
CONVERTED TO THREE-CARBON PYRUVIC
ACID.
 7. Glucose is a Stable molecule that DOES NOT
Break down Easily.
 8. For a Molecule of Glucose to undergo
Glycolysis, a Cell must First "SPEND" ATP to
energize the Glucose Molecule. The ATP
provides the Activation Energy needed to begin
Glycolysis.
 9. Although ATP (ENERGY) is used to begin
Glycolysis, the reactions that make up the
process eventually produce A NET GAIN OF TWO
ATP MOLECULES.
 10. Glycolysis is followed BY THE BREAK DOWN
OF PYRUVIC ACID.
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FOUR MAIN STEPS
 STEP 1 - TWO Phosphates are attached to
Glucose, forming a NEW Six-Carbon
Compound. The Phosphate Groups come From
TWO ATP, which are Converted to ADP.
 STEP 2 - The Six-Carbon Compound formed in
Step 1 is SPLIT into TWO Three-Carbon
Molecules of PGAL.
 STEP 3 - The TWO PGAL Molecules are
Oxidized, and each Receives a Phosphate Group
Forming Two NEW Three-Carbon
Compounds. The Phosphate Groups are
provided by Two molecules of NAD+ forming
NADH.
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Steps cont
 STEP 4 - The Phosphate Groups added in Step 1
and Step 3 are Removed from the Three-Carbon
Compounds. This reaction produces Two
molecules of Pyruvic Acid. Each Phosphate
Group is combines with a molecule of ADP to
make a molecule of ATP. Because a total of Four
Phosphate Groups were Added, FOUR
MOLECULES OF ATP ARE PRODUCED.
 TWO ATP Molecules were used in Step 1, but
FOUR are Produced in Step 4. Therefore,
Glycolysis has a NET YIELD of TWO ATP
Molecules for every Molecule of Glucose that is
converted into Pyruvic Acid. What happens to
the Pyruvic Acid depends on the Type of Cell and
on whether Oxygen is present.
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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

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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)
ADP
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Payola!
Finally some
ATP!
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
AP Biology
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