Download What do you know about Cellular Respiration?

What do you know
about Cellular Respiration?
What do you know about Cellular Respiration?
Shuttling Energy Sources
Across a Membrane!
• Different steps
occur in
different
locations of a
cell!
• Resources
need to be
moved across
the
mitochondrial
membrane
What do you know about Cell Respiration?
Energy Flow in the Ecosystem
Light
energy
ECOSYSTEM
CO2  H2O
Photosynthesis
in chloroplasts
Organic  O
2
molecules
Cellular respiration
in mitochondria
ATP
Heat
energy
ATP powers
most cellular work
Energy is generated
by Catabolic
pathways involved in
oxidizing organic
fuels
Catabolic Pathways
and ATP
Production



The breakdown of
organic molecules is
exergonic
Fermentation partial
sugar degradation
without O2
Aerobic respiration
consumes organic
molecules and O2 and
yields ATP
Cellular Respiration

AKA Aerobic Respiration = REQUIRES O2 to complete!

C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)

-ΔG: -686kcal/mol
Redox Reactions: Oxidation and Reduction

The transfer of
electrons during
chemical reactions
releases energy
stored in organic
molecules

This released
energy is ultimately
used to synthesize
ATP
The Principle of Redox:
Transfer of Electrons!
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
•In oxidation, a substance loses electrons, or is oxidized
(becomes more positive)
•In reduction, a substance gains electrons, or is reduced
(the amount of positive charge is reduced)
More Redox!
becomes oxidized
becomes reduced
 Electron donor is called the reducing agent
 Loses Electrons Oxidized (LEO)
 Electron receptor is called the oxidizing agent
 Gains Electrons Reduced (GER)
 Some redox reactions do not transfer electrons but change the
electron sharing in covalent bonds
Redox of Methane and Oxygen Gas
Reactants
Products
becomes oxidized
Energy
becomes reduced
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
Oxidation of Organic Fuel Molecules
During Cellular Respiration

Fuel (such as glucose) is oxidized, and O2 is reduced
becomes oxidized
becomes reduced

In general lots of C-H bonds make a great fuel source
Carbs: Why Are They Good Energy?
Electrons are
transferred in the
form of H atoms.
C-H bonds are
higher in energy. The
more C-H bonds the
more energy!
C6H12O6
O2
CO2
Loses Electrons
H2O
Gains Electrons
H is transferred from C to O, a lower
energy state  releases energy for ATP
formation
Redox in Respiration Occur in Steps


Enzymes control
release of
energy by H
transfer at key
steps!
Not directly to
O, but to
coenzyme to
make more
energy first!
Nicotinamide Adenine Dinucleotide (NAD)
and the Energy Harvesting
NAD
NADH
Dehydrogenase
Reduction of NAD
(from food)
Nicotinamide
(oxidized form)
Oxidation of NADH
Nicotinamide
(reduced form)
•Electrons from organic compounds
are usually first transferred to NAD+,
a coenzyme
•Each NADH (the reduced form of
NAD+) represents stored energy that
is tapped to synthesize ATP
Electron Removal From Glucose
Sugar-source
NADH
Dehydrogenase
Sugar-source
NAD+
Released into the
surrounding solution
Energy Production in the Electron Transport Chain
H2  1/2 O2

2H
1/
Explosive
release of
heat and light
energy
Free energy, G
Free energy, G
(from food via NADH)
Controlled
release of
+

2H  2e
energy for
synthesis of
ATP
O2
ATP
ATP
ATP
2 e
2
1/
H+
H2O
(a) Uncontrolled reaction
2
H2O
(b) Cellular respiration
2
O2
The Stages of Cellular Respiration: A Preview
1. Glycolysis (color-coded teal)  glucose to pyruvate
2. Pyruvate oxidation and the citric acid cycle
(color-coded salmon)  completes glucose breakdown
3. Oxidative phosphorylation: electron transport and
chemiosmosis (color-coded violet)  Most ATP synthesis
Glycolysis
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
MITOCHONDRION
CYTOSOL
ATP
Substrate-level
phosphorylation
Figure 9.6-2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
MITOCHONDRION
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Figure 9.6-3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
BioFlix: Cellular Respiration
© 2011 Pearson Education, Inc.
Substrate-level Phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
ATP
Product

A smaller amount of ATP is formed in glycolysis and the citric
acid cycle by substrate-level phosphorylation
Oxidative Phosphorylation
 The sum of all
the energyreleasing steps
in the
mitochondria
accounts for
almost 90% of
the ATP
generated
Glycolysis harvests
chemical energy by
oxidizing glucose to
pyruvate
Energy
Phases of
Glycolysis
Energy Investment Phase
Glucose
2 ADP  2 P
2 phases:
 Energy
investment
 Energy Payoff
2 ATP used
Energy Payoff Phase
4 ADP  4 P
No Carbon
released!
2 NAD+  4 e  4 H+
4 ATP formed
2 NADH  2 H+
2 Pyruvate  2 H2O
Does not depend
on oxygen!
Net
Glucose
4 ATP formed  2 ATP used
2 NAD+  4 e  4 H+
2 Pyruvate  2 H2O
2 ATP
2 NADH  2 H+
Figure 9.9-1
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
ADP
Hexokinase
1
Figure 9.9-2
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ADP
Hexokinase
1
Phosphoglucoisomerase
2
Figure 9.9-3
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
ADP
ADP
Hexokinase
1
Fructose 1,6-bisphosphate
Phosphoglucoisomerase
Phosphofructokinase
2
3
Figure 9.9-4
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
ADP
ADP
Hexokinase
1
Fructose 1,6-bisphosphate
Phosphoglucoisomerase
Phosphofructokinase
2
3
Aldolase
Dihydroxyacetone
phosphate
4
Glyceraldehyde
3-phosphate
Isomerase
5
To
step 6
Figure 9.9-5
Glycolysis: Energy Payoff Phase
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2Pi
1,3-Bisphosphoglycerate
Figure 9.9-6
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
Figure 9.9-7
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
2
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
8
2-Phosphoglycerate
Figure 9.9-8
Glycolysis: Energy Payoff Phase
2 ATP
2 H2O
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+2
H
2 ADP
2
2
1,3-Bisphosphoglycerate
7
Enolase
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
2
9
3-Phosphoglycerate
8
2-Phosphoglycerate
Phosphoenolpyruvate (PEP)
Figure 9.9-9
Glycolysis: Energy Payoff Phase
2 ATP
2 ATP
2 H2O
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
2
1,3-Bisphosphoglycerate
7
Enolase
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
9
3-Phosphoglycerate
8
2 ADP
2
2-Phosphoglycerate
Pyruvate
kinase
Phosphoenolpyruvate (PEP)
10
Pyruvate
Glycolysis
Glycolysis: Energy Investment Phase
Glucose
ATP
Fructose 6-phosphate
Glucose 6-phosphate
ADP
Hexokinase
1
Adds a phosphate =
energizing the glucose
Phosphoglucoisomerase
2
Isomerizes the
sugar!
Glycolysis
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
ATP
Fructose 1,6-bisphosphate
ADP
Cuts the
sugar in
half!
Phosphofructokinase
3
Second
energy
investment
Aldolase
Dihydroxyacetone
phosphate
Glyceraldehyde
3-phosphate
Isomerase
Switches the 3C sugar
between 2 forms
4
5
To
step 6
Glycolysis
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
+ 2 H
2 NAD
2 ADP
2
2
Triose
phosphate
dehydrogenase
6
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
Removes 2 H to make
an NADH and H+
7
3-Phosphoglycerate
Removes a phosphate to
make ATP!
Glycolysis
Glycolysis: Energy Payoff Phase
2 H2O
2
2
Shuffles the
phosphate to a
different carbon
8
2 ADP
2
Phosphoglyceromutase
3-Phosphoglycerate
2 ATP
Enolase
2-Phosphoglycerate
9
Pulls off
water
2
Pyruvate
kinase
Phosphoenolpyruvate (PEP)
10
Pyruvate
Makes
more ATP
Citric acid cycle
completes the
energy-yielding
oxidation of organic
molecules
Oxidation of Pyruvate to Acetyl CoA
MITOCHONDRION
CYTOSOL
CO2
Coenzyme A
3
1
2
Pyruvate
NAD
NADH + H
Acetyl CoA
Transport protein

This step is carried out by a multienzyme complex
that catalyses three reactions to bring pyruvate into
the mitochondria
Lose: 1 CO2 per pyruvate
Gain: 1 NADH per pyruvate
The Citric
Acid Cycle
Pyruvate
CO2
NAD
CoA
NADH



Completes the break
down of pyruvate to
CO2
The cycle oxidizes
organic fuel derived
from pyruvate,
generating 1 ATP, 3
NADH, and 1 FADH2
per turn
REMEMBER 2
pyruvate per Glucose!
+ H
Acetyl CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD
FADH2
3 NADH
FAD
+ 3 H
ADP + P i
ATP
Overview: Citric Acid Cycle
•
8 steps, each
catalyzed by a
specific enzyme
•
Acetyl combines with
oxaloacetatecitrate
•
The next seven
steps decompose
the citrate back to
oxaloacetate,
making the process
a cycle
Acetyl CoA
CoA-SH
1
Oxaloacetate
Citrate
Citric
acid
cycle
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
3
NADH
+ H
CO2
-Ketoglutarate
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
NAD
NADH
Succinyl
CoA
+ H
CO2
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
CoA-SH
5
NAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Acetyl CoA
CoA-SH
NADH
+ H
H2O
1
NAD
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Acetyl group (What’s left of the
pyruvate) combines with
Oxaloacetate to make Citrate
Acetyl CoA
CoA-SH
H 2O
1
Citrate is
isomerized by
removing
water and then
adding it back
Oxaloacetate
2
Citrate
Isocitrate
Isocitrate is
oxidized (Loses
2 H) and
reduces NAD+
A second
reaction occurs,
removing CO2
Isocitrate
NAD
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
NAD
NADH
Succinyl
CoA
+ H
CO2
More CO2 is lost,
and another NAD+
is reduced.
Coenzyme A
makes another
appearance
A phosphate group
replaces CoA. The
Phosphate is then
transferred to GDP to
make GTP
Fumarate
6
CoA-SH
5
FADH2
FAD
Succinate
Succinate is
oxidized by FAD to
make FADH2
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
Another
redox to
make NADH
and
oxaloacetate
NAD
8 Oxaloacetate
Malate
H 2O
Water molecule
added to rearrange
bonds
7
Fumarate
During oxidative
phosphorylation,
chemiosmosis couples
electron transport to
ATP synthesis
The Pathway of
Electron Transport


Occurs in the inner
membrane (cristae) of
the mitochondrion
Most of the chain’s
components are
proteins, which exist in
multiprotein complexes
The carriers alternate
reduced and oxidized
states as they accept
and donate electrons
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)

NADH
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
NADH and FADH2 Bring electrons to the ETC



Electrons are
passed through a
number of proteins
including
cytochromes
(each with an iron
atom) to O2
no ATP directly
generated
Release energy in
small steps
Oxidative Phosphorylation and the ETC
H
H

H
Protein
complex
of electron
carriers
Cyt c
Q
I
IV
III
II
FADH2 FAD
NADH
H
2 H + 1/2O2
ATP
synthase
H2O
NAD
ADP  P i
(carrying electrons
from food)
ATP
H
1 Electron transport chain
2 Chemiosmosis
Oxidative phosphorylation
Electron transfer is coupled with H+ pumping into
intermembrane space of mitchondria
Chemiosmosis: Energy-Coupling
Mechanism
Using H+ Gradient to do Work
INTERMEMBRANE SPACE
H
Stator
Rotor




The H+ gradient is referred to as
a proton-motive force
H+ then moves back across the
membrane, passing through the
proton, ATP synthase
ATP synthase uses the exergonic
flow of H+ to drive
phosphorylation of ATP
H+ generated by ETC coupled
with ATP synthesis!
Internal
rod
Catalytic
knob
ADP
+
Pi
ATP
MITOCHONDRIAL MATRIX
Accounting of ATP
Production by Cellular Respiration



During cellular respiration, most energy flows in
this sequence:
glucose  NADH  electron transport chain
 proton-motive force  ATP
About 34% of the energy in a glucose molecule
is transferred to ATP during cellular respiration,
making about 32-36 ATP
There are several reasons why the number of
ATP is not known exactly
Figure 9.16
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
CYTOSOL
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
Fermentation and
anaerobic
respiration enable cells
to produce ATP without
the use of oxygen
Anaerobic Respiration
Oxygen is
not used or
may be
poisonous!

Certain fungi and bacteria undergo
Glycolysis coupled to an electron
transport chain but use other molecules
as final electron acceptors like sulfate!
Fermentation: Anaerobic Respiration
Using Substrate Level Phosphorylation
Fermentation consists of
glycolysis plus reactions that
regenerate NAD+
Without NAD+
Glycolysis
couldn’t happen
Animation: Fermentation Overview
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Fermentation
2 ADP  2 P
Glucose
i
2 ADP  2 P
2 ATP
Glycolysis
Glucose
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD 
2 Ethanol
(a) Alcohol fermentation


2 NADH
 2 H
2 NAD 
2 CO2
2 Acetaldehyde
2 NADH
 2 H
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
In alcohol fermentation, pyruvate is converted to
ethanol in two steps, with the first releasing CO2
In lactic acid fermentation, pyruvate is reduced to
NADH, forming lactate with no release of CO2
Figure 9.17a
2 ADP  2 P i
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD 
2 Ethanol
(a) Alcohol fermentation
2 NADH
 2 H
2 CO2
2 Acetaldehyde
2 ADP  2 P i
Glucose
2 ATP
Glycolysis
2 NADH
 2 H
2 NAD 
2 Pyruvate

2 Lactate
(b) Lactic acid fermentation
Lactic acid fermentation by
some fungi and bacteria is
used to make cheese and
yogurt, and human muscles
when O2 is scarce
Importance
of Pyruvate
Glucose
CYTOSOL
Glycolysis
Pyruvate
Obligate
anaerobes –
Oxygen is
poisonous!
Facultative
anaerobes –
can go either
way
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
Citric
acid
cycle
Glycolysis and the
citric acid cycle
connect to many
other metabolic
pathways
Catabolism of Various
Food Sources
Proteins
Carbohydrates
Amino
acids
Sugars
Glycolysis
Glycolysis accepts a wide
range of carbohydrates
Glucose
Glyceraldehyde 3- P
Fatty acids are broken
down by beta oxidation
and yield acetyl CoA
An oxidized gram of fat
produces more than twice
as much ATP as an
oxidized gram of
carbohydrate
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Fats
Glycerol Fatty
acids
Biosynthesis
(Anabolic Pathways)

The body uses small
molecules to build
other substances

These small
molecules may
come directly from
food, from
glycolysis, or from
the citric acid cycle
Glucose
Feedback Mechanisms
and Cell Respiration
AMP
Glycolysis
Fructose 6-phosphate

•Feedback inhibition is the
most common mechanism
for control
•If ATP concentration
begins to drop, respiration
speeds up; when there is
plenty of ATP, respiration
slows down
Stimulates

Phosphofructokinase

Fructose 1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Fermentation vs. Anaerobic vs. Aerobic
Respiration




All use glycolysis (net ATP = 2) to oxidize glucose
and harvest chemical energy of food
In all three, NAD+ is the oxidizing agent that
accepts electrons during glycolysis
The processes have different final electron
acceptors: an organic molecule (such as pyruvate
or acetaldehyde) in fermentation and O2 in cellular
respiration
Cellular respiration produces 32 ATP per glucose
molecule; fermentation produces 2 ATP per glucose
molecule
Figure 9.UN06
Inputs
Outputs
Glycolysis
Glucose
2 Pyruvate  2
ATP
 2 NADH
Figure 9.UN07
Outputs
Inputs
2 Pyruvate
2 Acetyl CoA
2 Oxaloacetate
Citric
acid
cycle
2
ATP
8 NADH
6
CO2
2 FADH2
Figure 9.UN08
H
INTERMEMBRANE
SPACE
H
H
Cyt c
Protein complex
of electron
carriers
IV
Q
III
I
II
FADH2 FAD
NAD
NADH
(carrying electrons from food)
2 H + 1/2 O2
MITOCHONDRIAL MATRIX
H2O
Figure 9.UN09
INTERMEMBRANE
SPACE
H
ATP
synthase
MITOCHONDRIAL
MATRIX
ADP + P i
H
ATP
pH difference
across membrane
Figure 9.UN10
Time
Figure 9.UN11