Cellular Respiration Stage 1: Glycolysis (Ch....
Transcript of Cellular Respiration Stage 1: Glycolysis (Ch....
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Cellular Respiration
Stage 1:
Glycolysis (Ch. 6)
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2007-2008
What’s thepoint?
The pointis to make
ATP!
ATP
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Harvesting stored energy• Energy is stored in organic molecules
– carbohydrates, fats, proteins
• Heterotrophs eat these organic molecules food
– digest organic molecules to get…
• raw materials for synthesis
• fuels for energy
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Harvesting stored energy• Glucose is the model
– catabolism of glucose to produce ATP
C6H12O6 6O2ATP 6H2O 6CO2+ + +
CO2 + H2O + heatfuel
(carbohydrates)
COMBUSTION = making a lot of heat energy
by burning fuels in one step
RESPIRATION = making ATP (& some heat)
by burning fuels in many small steps
CO2 + H2O + ATP (+ heat)
ATP
glucose
glucose + oxygen energy + water + carbondioxide
res
pir
ati
on
O2 O2
+ heat
enzymesATP
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How do we harvest energy from fuels?
• Digest large molecules into smaller ones
– break bonds & move electrons from one molecule to another
• as electrons move they “carry energy” with them
• that energy is stored in another bond, released as heat or harvested to make ATP
e-
+ +e-
+ –loses e- gains e- oxidized reduced
oxidation reduction
redox
e-
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How do we move electrons in biology?• Moving electrons in living systems
– electrons cannot move alone in cells
• electrons move as part of H atom
• move H = move electronsp
e
+
H
+H
+ –loses e- gains e- oxidized reduced
oxidation reduction
C6H12O6 6O2 6CO2 6H2O ATP+ + +
oxidation
reductionHe-
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Coupling oxidation & reduction• REDOX reactions in respiration
– release energy (break C-C bonds in organics)
• Strip electrons from C-H bonds: remove H atoms
• electrons attracted to more electronegative atoms
– in biology, the most electronegative atom?
–O2 H2O = oxygen has been reduced
– couple REDOX reactions & use the released energy to synthesize ATP
C6H12O6 6O2 6CO2 6H2O ATP+ + +
oxidation
reduction
O2
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Oxidation & reduction
• Oxidation
– adding O
– removing H
– loss of electrons
– releases energy
– exergonic
• Reduction
– removing O
– adding H
– gain of electrons
– stores energy
– endergonic
C6H12O6 6O2 6CO2 6H2O ATP+ + +
oxidation
reduction
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Moving electrons in respiration
• Electron carriers move electrons by shuttling H atoms around
– NAD+ NADH (reduced)
– FAD+2 FADH2 (reduced)
+ Hreduction
oxidation
PO–
O–
O
–O
PO–
O–
O
–O
CC
O
NH2
N+
H
adenine
ribose sugar
phosphates
NAD+
nicotinamide
Vitamin B3
niacin
PO–
O–
O
–O
PO–
O–
O
–O
CC
O
NH2
N+
HNADH
carries electrons as a reduced molecule
reducing power!
H
like $$in the bank
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Overview of cellular respiration• 4 metabolic stages
– Anaerobic respiration
1. Glycolysis
–respiration without O2
– in cytosol
– Aerobic respiration
–respiration using O2
– in mitochondria
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain
C6H12O6 6O2 ATP 6H2O 6CO2+ + + (+ heat)
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Glycolysis
glucose pyruvate
2x6C 3C
In thecytosol?Why doesthat makeevolutionary
sense?
• Breaking down glucose
– “glyco – lysis” (splitting sugar)
– ancient pathway which harvests energy
• where energy transfer first evolved
• still is starting point for ALL cellular respiration
– but it’s inefficient
• generate only 2 ATP for every 1 glucose
– occurs in cytosol
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Evolutionary perspective• Prokaryotes
– first cells had no organelles
• Anaerobic atmosphere– life on Earth first evolved without free oxygen (O2) in
atmosphere
– energy had to be captured from organic molecules in absence of O2
• Prokaryotes that evolved glycolysis are ancestors of all modern life– ALL cells still utilize glycolysis
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10 reactions– convert
glucose (6C) to 2 pyruvate (3C)
– produces:4 ATP & 2 NADH
– consumes:2 ATP
– net yield:2 ATP & 2 NADH
glucoseC-C-C-C-C-C
fructose-1,6bPP-C-C-C-C-C-C-P
DHAPP-C-C-C
G3PC-C-C-P
pyruvateC-C-C
Overview
DHAP = dihydroxyacetone phosphate
G3P = glyceraldehyde-3-phosphate
ATP2
ADP2
ATP4
ADP4
NAD+2
2Pi
enzyme
enzyme
enzyme enzyme
enzyme
enzyme
enzyme
enzyme
2Pi
2H
2
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Glycolysis summary
endergonic
invest some ATP
exergonic
harvest a little
ATP & a little NADH
net yield
2 ATP
2 NADH
4 ATP
ENERGY INVESTMENT
ENERGY PAYOFF
G3PC-C-C-P
NET YIELD
like $$in the bank
-2 ATP
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Pi
3
6
4,5
ADP
NAD+
Glucose
hexokinase
phosphoglucose
isomerase
phosphofructokinase
Glyceraldehyde 3
-phosphate (G3P)
Dihydroxyacetone
phosphate
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
isomerase
glyceraldehyde3-phosphate
dehydrogenase
aldolase
1,3-Bisphosphoglycerate
(BPG)
1,3-Bisphosphoglycerate
(BPG)
1
2
ATP
ADP
ATP
NADH
NAD+
NADH
Pi
CH2
C O
CH2OH
P O
CH2 O P
O
CHOH
C
CH2 O P
O
CHOH
CH2 O PO
CH2OP
O
PO
CH2
H
CH2OHO
CH2 POO
CH2OH
P O
1st half of glycolysis (5 reactions)
Glucose “priming”
get glucose ready
to split
phosphorylate
glucose
molecular
rearrangement
split destabilized
glucose
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2nd half of glycolysis (5 reactions)
Payola!Finally some
ATP!
7
8
H2O9
10
ADP
ATP
3-Phosphoglycerate(3PG)
3-Phosphoglycerate(3PG)
2-Phosphoglycerate(2PG)
2-Phosphoglycerate(2PG)
Phosphoenolpyruvate(PEP)
Phosphoenolpyruvate(PEP)
Pyruvate Pyruvate
phosphoglyceratekinase
phosphoglycero-mutase
enolase
pyruvate kinase
ADP
ATP
ADP
ATP
ADP
ATP
H2O
CH2OH
CH3
CH2
O-
O
C
PH
CHOH
O-
O-
O-
C
C
C
C
C
C
P
P
O
O
O
O
O
O
CH2
NAD+
NADH
NAD+
NADH
Energy HarvestG3P
C-C-C-P
PiPi 6
DHAPP-C-C-C
– NADH production• G3P donates H
• oxidizes the sugar
• reduces NAD+
• NAD+ NADH
– ATP production• G3P pyruvate
• PEP sugar donates P– “substrate level
phosphorylation”
• ADP ATP
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Energy accounting of glycolysis
• Net gain = 2 ATP + 2 NADH– some energy investment (-2 ATP)
– small energy return (4 ATP + 2 NADH)
• 1 6C sugar 2 3C sugars
2 ATP 2 ADP
4 ADP
glucose pyruvate
2x6C 3C
All that work! And that’s all
I get?
ATP4
2 NAD+ 2 Butglucose has
so much moreto give!
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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
• no O2 = slow growth, slow reproduction
• only harvest 3.5% of energy stored in glucose
–more carbons to strip off = more energy to harvest
Hard wayto makea living!
O2
O2
O2
O2
O2
glucose pyruvate
6C 2x 3C
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7
8
H2O9
10
ADP
ATP
3-Phosphoglycerate(3PG)
3-Phosphoglycerate(3PG)
2-Phosphoglycerate(2PG)
2-Phosphoglycerate(2PG)
Phosphoenolpyruvate(PEP)
Phosphoenolpyruvate(PEP)
Pyruvate Pyruvate
ADP
ATP
ADP
ATP
ADP
ATP
H2O
NAD+
NADH
NAD+
NADH
PiPi 6
Glycolysis
glucose + 2ADP + 2Pi + 2 NAD+ 2 pyruvate + 2ATP + 2NADH
But can’t stop there!
• Going to run out of NAD+
– without regenerating NAD+,energy production would stop!
– another molecule must accept H from NADH, so NAD+ is freed up for another round
PiNAD+
G3P
1,3-BPG 1,3-BPG
NADH
NAD+
NADH
Pi
DHAP
raw materials products
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NADH
pyruvate
acetyl-CoA
lactate
ethanol
NAD+
NAD+
NADH
NAD+
NADH
CO2
acetaldehyde
H2O
Krebscycle
O2
lactic acid
fermentation
with oxygen
aerobic respiration
without oxygen
anaerobic respiration“fermentation”
How is NADH recycled to NAD+?Another molecule must accept H from NADH
recycle
NADH
which path you
use depends on
who you are…alcohol
fermentation
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Fermentation (anaerobic)
• Bacteria, yeast
1C3C 2C
pyruvate ethanol + CO2
Animals, some fungi
pyruvate lactic acid
3C 3C
beer, wine, bread
cheese, anaerobic exercise (no O2)
NADH NAD+
NADH NAD+
back to glycolysis
back to glycolysis
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recycle
NADH
Reversible process
once O2 is available,
lactate is converted
back to pyruvate by
the liver
Lactic Acid Fermentation
pyruvate lactic acid
3C 3C
NADH NAD+
O2
animals
some fungi
back to glycolysis
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recycle
NADH
Alcohol Fermentation
1C3C 2C
pyruvate ethanol + CO2
NADH NAD+
Dead end process at ~12% ethanol,
kills yeast
can’t reverse the
reaction
bacteria
yeast
back to glycolysis
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Pyruvate is a branching point
Pyruvate
O2O2
mitochondria
Krebs cycle
aerobic respiration
fermentationanaerobicrespiration
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2007-2008
What’s thepoint?
The pointis to make
ATP!
ATP