Download Ch. 9: Cellular Respiration

+
Chapter 9:
Cellular
Respiration:
Harvesting
Chemical Energy
AP Biology
+ Overview: Life Is Work




Living cells require energy from outside sources
Herbivore: giant panda, obtain energy by eating plants
Carnivore: hyena eats other animals
Omnivore: squirrel eats insects and seeds and chicken legs?
+

Energy flows into
ecosystem as
sunlight and leaves
as heat

Photosynthesis
O2 &organic
molecules (used in
cellular respiration)

Cells use chemical
energy stored in
organic molecules
to regenerate ATP,
which powers work
Concept 9.1: Catabolic pathways yield
+ energy by oxidizing organic fuels







MULTIPLE processes central to cellular
respiration and related pathways
Breakdown of organic molecules is
exergonic
Cellular respiration: includes both
aerobic and anaerobic respiration;
often used to refer to aerobic
respiration
Aerobic respiration: consumes
organic molecules and O2; yields ATP
Anaerobic respiration: similar to
aerobic respiration but consumes
compounds other than O2
Fermentation: partial degradation of sugars that occurs without O2
Carbohydrates, fats, and proteins all consumed as fuel, however it is
helpful to trace cellular respiration with the sugar glucose:
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Redox
Reactions:
+
Oxidation and Reduction





Transfer of electrons during chemical reactions releases energy stored in
organic molecules

used to synthesize ATP


Oxidation Is Loss
Reduction Is Gain
Redox reactions: oxidation-reduction reactions; chemical reactions that
transfer electrons between reactants
Oxidation: substance loses electrons, or is oxidized
Reduction: substance gains electrons, or is reduced (the amount of
positive charge is reduced)
REMEMBER: OIL-RIG
Fig. 9-UN1
+
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
+



Reducing agent: electron donor
Oxidizing agent: electron receptor is called the
Some redox reactions do not transfer electrons but change electron
sharing in covalent bonds

Ex: reaction between methane and O2
Oxidation of Organic Fuel Molecules
+
During Cellular Respiration

During cellular respiration, the fuel (such as glucose) is
oxidized, and O2 is reduced:
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the
+ Electron Transport Chain


Cellular respiration: glucose & other organic molecules broken
down in a series of steps
NAD+: Electrons from organic compounds usually first transferred to
NAD+, a coenzyme


NADH: reduced form of NAD+



represents stored energy that is tapped to synthesize ATP
NADH passes electrons to electron transport chain


functions as oxidizing agent during cellular respiration
passes electrons in series of steps instead of one EXPLOSIVE reaction
O2 pulls electrons down chain in an energy-yielding tumble
Energy yielded is used to regenerate ATP
Fig. 9-5
+
H2 + 1/2 O2
2H
(from food via NADH)
Controlled
release of
+
–
2H + 2e
energy for
synthesis of
ATP
1/
2 O2
Explosive
release of
heat and light
energy
1/
(a) Uncontrolled reaction
(b) Cellular respiration
2 O2
The Stages of Cellular Respiration: A
+
Preview

Three stages:

Glycolysis: breaks down glucose into two molecules of pyruvate

Citric acid cycle: completes the breakdown of glucose

Oxidative phosphorylation: accounts for most of the ATP synthesis
Fig. 9-6-1
+
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
ATP
Substrate-level
phosphorylation
Fig. 9-6-2
+
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Mitochondrion
Cytosol
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Fig. 9-6-3
+
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
+ ATP Production


Oxidative phosphorylation: process that generates most of the
ATP

powered by redox reactions

accounts for almost 90% of the ATP generated by cellular respiration
Substrate-level phosphorylation: produces smaller amount of ATP
in glycolysis and the citric acid cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
+
Concept 9.2: Glycolysis harvests chemical
energy by oxidizing glucose to pyruvate

Glycolysis or
“splitting of sugar”
breaks down glucose
into two molecules of
pyruvate

Glycolysis occurs in
the cytoplasm and
has two major
phases:

Energy investment
phase

Energy payoff phase
+
Glycolysis

Consists of series of chemical reactions catalyzed by specific
enzymes

Takes place in cytosol of cell

Four main steps

6-C glucose  Two 3-C
pyruvic acid

one six-carbon molecule
of glucose is oxidized to
produce TWO three-carbon
molecule of pyruvic acid
+
Step 1

Two phosphate groups attached to glucose forming new 6-C
compound

Phosphate groups supplied by two ATP molecules

2 ATP used  2 ADP
+
Step 2

6-C compound split into 2 PGAL molecules
+
Step 3

Both PGAL molecules are oxidized and receive phosphate
group

2 NADH  2 NAD+

Product: New 3-C compound
+
Step 4

Phosphate groups added in Steps 1&3 removed from 3-C
compounds formed in Step 3

THUS! we get 2 pyruvic acid molecules

Each phosphate group is added to ADP to give us.......ATP!!!!!!!!!

Total: 4 ATP
+
Let’s talk numbers...

Two ATP used in Step 1

Four ATP produced in Step 4

Net Yield: Two ATP
Fig. 9-9-1
+
Glucose
ATP
1
Hexokinase
ADP
Glucose
Glucose-6-phosphate
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
Fig. 9-9-2
+
Glucose
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
Fig. 9-9-3
+
Glucose
ATP
1
Hexokinase
ADP
Fructose-6-phosphate
Glucose-6-phosphate
2
Phosphoglucoisomerase
ATP
3
Phosphofructokinase
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
ADP
Fructose1, 6-bisphosphate
Fructose1, 6-bisphosphate
Fig. 9-9-4
+
Glucose
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose1, 6-bisphosphate
4
Fructose-6-phosphate
ATP
Aldolase
3
Phosphofructokinase
ADP
5
Isomerase
Fructose1, 6-bisphosphate
4
Aldolase
5
Isomerase
Dihydroxyacetone
phosphate
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Glyceraldehyde3-phosphate
Fig. 9-9-5
+
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
Glyceraldehyde3-phosphate
2 NAD+
2 NADH
6
Triose phosphate
dehydrogenase
2 Pi
+ 2 H+
2 1, 3-Bisphosphoglycerate
Fig. 9-9-6
+
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
2 1, 3-Bisphosphoglycerate
2 ADP
2
3-Phosphoglycerate
2 ATP
2
7
Phosphoglycerokinase
3-Phosphoglycerate
Fig. 9-9-7
+
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
3-Phosphoglycerate
8
2
3-Phosphoglycerate
Phosphoglyceromutase
2
8
Phosphoglyceromutase
2-Phosphoglycerate
2
2-Phosphoglycerate
Fig. 9-9-8
+
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
3-Phosphoglycerate
2
2-Phosphoglycerate
8
Phosphoglyceromutase
9
2
2 H2O
2-Phosphoglycerate
Enolase
9
Enolase
2 H2O
2
Phosphoenolpyruvate
2
Phosphoenolpyruvate
Fig. 9-9-9
+
2 NAD+
6
Triose phosphate
dehydrogenase
2 Pi
2 NADH
+ 2 H+
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
Phosphoenolpyruvate
2 ADP
2
3-Phosphoglycerate
8
Phosphoglyceromutase
2 ATP
2
10
Pyruvate
kinase
2-Phosphoglycerate
9
2 H2O
Enolase
2 Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
2
Pyruvate
Pyruvate
+ Energy Yield

Kilocalorie- 1,000 calories; often unit used to measure energy

Complete oxidation on ONE glucose molecule= 686 kcal

One ADP One ATP absorbs 12 kcal

Can you calculate
the efficiency of
glycolysis?


2 ATP produced
Percent usually a
calculation x100
+
Efficiency of Glycolysis
+
What does that mean?!

Two ATP molecules produces during glycolysis only use small
percentage of energy that could be released from glucose

SO! anaerobic pathways are NOT very efficient

Probably evolved
before aerobic
pathways
Concept 9.3: The citric acid cycle completes
+
energy-yielding oxidation of organic molecules



In presence of O2, pyruvate enters the mitochondrion
Before citric acid cycle can begin, pyruvate must be converted to
acetyl CoA, which links the cycle to glycolysis
Citric acid cycle also called the Krebs cycle


takes place within the mitochondrial matrix
oxidizes organic fuel derived from pyruvate, generating…
 1 ATP
 3 NADH
 1 FADH2 per turn
Fig. 9-11
+
Pyruvate
CO2
NAD+
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle
FADH2
2 CO2
3 NAD+
3 NADH
FAD
+ 3 H+
ADP + P i
ATP
+
•
•
Eight steps, each catalyzed by a
specific enzyme
Acetyl group of acetyl CoA joins cycle
by combining with oxaloacetate,
forming citrate
•
•
•
Citric Acid Cycle
Acetyl CoA + Oxaloacetate = Citrate
Next seven steps decompose the
citrate
back to oxaloacetate, making the
process a cycle
NADH and FADH2 produced by cycle
relay electrons extracted from food
to the electron transport chain
Fig. 9-12-1
+
Acetyl CoA
CoA—SH
1
Oxaloacetate
Citrate
Citric
acid
cycle
Fig. 9-UN6
+
Inputs
Outputs
S—CoA
C
2
ATP
6
NADH
O
CH3
2
Acetyl CoA
O
C
COO
CH2
COO
2
Oxaloacetate
Citric acid
cycle
2 FADH2
Fig. 9-12-2
+
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
Fig. 9-12-3
+
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
3
NADH
+ H+
CO2
-Ketoglutarate
Fig. 9-12-4
+
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
+ H+
3
CO2
CoA—SH
-Ketoglutarate
4
NAD+
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-5
+
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
+ H+
3
CO2
CoA—SH
-Ketoglutarate
4
CoA—SH
5
NAD+
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-6
+
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
+ H+
3
CO2
Fumarate
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-7
+
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
NADH
+ H+
3
CO2
Fumarate
CoA—SH
-Ketoglutarate
4
6
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-8
+
Acetyl CoA
CoA—SH
NADH
+H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
NADH
+ H+
3
CO2
Fumarate
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
+

Following glycolysis and citric acid cycle, NADH and FADH2
account for most of energy extracted from food


Concept 9.4: During oxidative phosphorylation,
chemiosmosis couples electron transport to ATP synthesis
NADH and FADH2 donate electrons to electron transport chain, which
powers ATP synthesis via oxidative phosphorylation
Electron transport chain is in cristae of mitochondrion

Most of chain’s components are proteins, which exist in multiprotein
complexes

Carriers alternate
reduced and oxidized
states as they accept
and donate electrons

Electrons drop in free
energy as they go down
the chain and are finally
passed to O2, forming H2O
Fig. 9-UN7
+
INTERMEMBRANE
SPACE
H+
ATP
synthase
ADP + P i
MITOCHONDRIAL
MATRIX
ATP
H+

+



Electrons transferred from NADH or FADH2 to the electron
transport chain
Electrons passed through a number of proteins including
cytochromes (each with an iron atom) to O2
Electron transport chain generates no ATP
ETC function: break the large free-energy drop from food to O2
into smaller steps that release energy in manageable amounts
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-13
+
NADH
50
2 e–
NAD+
FADH2
2 e–
40

FMN
FAD
Multiprotein
complexes
FAD
Fe•S 
Fe•S
Q

Cyt b
30
Fe•S
Cyt c1
I
V
Cyt c
Cyt a
Cyt a3
20
10
2 e–
(from NADH
or FADH2)
0
2 H+ + 1/2 O2
H2O
Chemiosmosis: The Energy-Coupling
+
Mechanism
 Electron
transfer in ETC
causes proteins to pump H+
from mitochondrial matrix to
intermembrane space
 What
kind of energy is this
creating?
 H+
then moves back across
membrane, passing through
channels in ATP synthase
 ATP
synthase uses exergonic
flow of H+ to drive
phosphorylation of ATP
 This
is example of
chemiosmosis

use of energy in a H+ gradient
to drive cellular work
Fig. 9-15
Magnetic bead
Electromagnet
Sample
Internal
rod
Catalytic
knob
Nickel
plate
RESULTS
Rotation in one direction
Rotation in opposite direction
Number of photons
detected (103)
+
EXPERIMENT
No rotation
30
25
20
0
Sequential trials
Fig. 9-15a
+
EXPERIMENT
Magnetic bead
Electromagnet
Sample
Internal
rod
Catalytic
knob
Nickel
plate
Fig. 9-15b
+ RESULTS
Rotation in one direction
Rotation in opposite direction
No rotation
30
25
20
0
Sequential trials
stored in a H gradient across membrane couples the
+  Energy
redox reactions of the electron transport chain to ATP
+

synthesis
Proton-motive force: H+ gradient, name emphasizes its
capacity to do work
+ Let’s remember…

Glycolysis  TWO pyruvic acid molecules

TWO pyruvic acid 
TWO acetyl CoA

SO, 1 glycolysis cycle
= 2 turns of Krebs
Cycle

2 Krebs Cycle
produces:




6 NADH
2 FADH2
2 ATP
4 CO2
+ Energy Yield
Glycolysis: 2 ATP
 Krebs Cycle: 2 ATP
 Each NADH molecule that supplies
ETC can generate 3 ATP
 Each FADH2 can generate 2 ATP
 10 NADH and 2 FADH2 made by
aerobic respiration
 How many ATP from the NADH and
FADH2?
 During cellular respiration, most energy
flows in this sequence:

glucose  NADH  electron transport chain  proton-motive force  ATP

About 40% of energy in a glucose molecule is transferred to ATP
during cellular respiration
+ How much
energy total?!

10 NADH 30 ATP

2 FADH2 4 ATP

Glycolysis 2 ATP

Krebs 2 ATP

TOTAL: 38 ATP
+
In reality…
 Real
number of ATP varies cell
to cell
 Eukaryotic
cells cannot diffuse
NADH through inner mito.
membrane
 SO!
Active transport needed 
Uses ATP
 38-2=36
+
Efficiency of Aerobic Respiration
 Almost
20x more efficient
Fig. 9-17
+
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
2
Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
6 NADH
2 NADH
2
Acetyl
CoA
+ 2 ATP
Citric
acid
cycle
+ 2 ATP
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
Concept 9.5: Fermentation and anaerobic
+respiration enable cells to produce ATP without
the use of oxygen




Most cellular respiration requires O2 to produce ATP
Glycolysis can produce ATP with or without O2 (in aerobic or
anaerobic conditions)
In absence of O2, glycolysis couples with fermentation or anaerobic
respiration to produce ATP
Anaerobic respiration uses
ETC with an electron
acceptor other than O2


Ex: sulfate
Fermentation uses
phosphorylation instead of
ETC to generate ATP
+ Types of Fermentation

Fermentation consists of glycolysis plus
reactions that regenerate NAD+, which can
be reused by glycolysis *CYCLE*

Two common types:

alcohol fermentation

lactic acid fermentation
+ Alcoholic Fermentation

Pyruvate converted to ethanol in two steps; first releasing CO2


CO2 released = carbonation in beer
Alcohol fermentation by yeast is used in brewing, winemaking,
and baking
+ Lactic Acid Fermentation

Pyruvate reduced to NADH, forming lactate as an end product,
with no release of CO2

LAF in some fungi and bacteria is used to make cheese and yogurt

Human muscle cells use lactic
acid fermentation to generate
ATP when O2 is scarce

Cramp = LA build up when LAF
overused when no O2 available
Fermentation vs Aerobic Respiration
+

Both:


use glycolysis to oxidize glucose
and other organic fuels to
pyruvate
Different:


ATP produced per glucose
molecule:

Fermentation: 2 ATP

Cellular Respiration: 38 ATP
Anaerobes:

Fermentation: Obligate
anaerobes carry out it or;
cannot survive in presence of O2


Yeast and many bacteria are
facultative anaerobes

can survive using either fermentation or cellular respiration

pyruvate is a fork in the metabolic road that leads to two alternative catabolic
routes
final electron acceptors:


Fermentation: an organic molecule (such as pyruvate or acetaldehyde)
Cellular respiration: O2 in cellular respiration
Fig. 9-19
Glucose
+
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
+ Evolutionary Significance of Glycolysis

Glycolysis:



occurs in nearly all organisms
probably evolved in ancient prokaryotes before there was oxygen in
atmosphere
Gycolysis and citric
acid cycle are major
intersections to
various catabolic
and anabolic pathways
+ Versatility of Catabolism



Catabolic pathways funnel e- from many
kinds of organic molecules into cellular
respiration
Glycolysis accepts wide range of
carbohydrates
Break it down and reuse…





Proteins must be digested to amino acids 
amino groups can feed glycolysis or the
citric acid cycle
Fats digested to glycerol  used in
glycolysis; fatty acids used in generating
acetyl CoA)
Fatty acids broken down by beta oxidation
 yield acetyl CoA
Oxidized gram of fat produces more than
twice as much ATP as an oxidized gram of
carbohydrate
BIG PICTURE: What does this mean in
terms of YOUR diet?
+Biosynthesis (Anabolic
Pathways)

Body uses small molecules
to build other substances

These small molecules may
come directly from food,
glycolysis, OR citric acid
cycle
Regulation of Cellular
+ Respiration via
Feedback Mechanisms

Feedback inhibition is most
common mechanism for control

ATP concentration drops 
respiration speeds up;

Plenty of ATP  respiration
slows down

Control of catabolism based
mainly on regulating activity of
enzymes at strategic points in
the catabolic pathway
+You should now be able to:
1.
Explain in general terms how redox reactions are involved in
energy exchanges
2.
Name the three stages of cellular respiration; for each, state the
region of the eukaryotic cell where it occurs and the products that
result
3.
In general terms, explain the role of the electron transport chain in
cellular respiration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
+
4.
Explain where and how the respiratory electron transport chain
creates a proton gradient
5.
Distinguish between fermentation and anaerobic respiration
6.
Distinguish between obligate and facultative anaerobes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings