Download Chapter 9 – Respiration

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 9
Cellular Respiration and
Fermentation
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
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
– controlled release of energy
– “burning” fuels in a series of
step-by-step enzyme-controlled reactions
Figure 9.2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2  H2O
Cellular respiration
in mitochondria
ATP
Heat
energy
Organic
 O2
molecules
ATP powers
most cellular work
Living economy
• Fueling the body’s economy
– eat high energy organic molecules
• food = carbohydrates, lipids, proteins, nucleic acids
– break them down
• digest = catabolism
– capture released energy in a form the cell can use
• Need an energy currency
– a way to pass energy around
– need a short term energy
storage molecule
Whoa!
Hot stuff!
ATP
ATP
• Adenosine TriPhosphate
– modified nucleotide
• nucleotide =
adenine + ribose + Pi  AMP
• AMP + Pi  ADP
• ADP + Pi  ATP
– adding phosphates is endergonic
How efficient!
Build once,
use many ways
high energy bonds
How does ATP store energy?
ADP
AMP
ATP
I think
he’s a bit
unstable…
don’t you?
O– O– O–
–O
– –O
–
OP
P –O
OP
OP
O–
O O O
• Each negative PO4 more difficult to add
– a lot of stored energy in each bond
• most energy stored in 3rd Pi
• 3rd Pi is hardest group to keep bonded to molecule
• Bonding of negative Pi groups is unstable
– spring-loaded
– Pi groups “pop” off easily & release energy
Instability of its P bonds makes ATP an excellent energy donor
How does ATP transfer energy?
ATP
ADP
O– O– O–
–OP –O
– –O
–
OP
OP
O–
O O O
O–
–OP O– +
O
• ATP  ADP
– releases energy
• ∆G = -7.3 kcal/mole
• Fuel other reactions
• Phosphorylation
– released Pi can transfer to other molecules
• destabilizing the other molecules
– enzyme that phosphorylates = “kinase”
7.3
energy
ATP / ADP cycle
Can’t store ATP
cellular
 good energy donor,
not good energy storage respiration
ATP
7.3
kcal/mole
 too reactive
 transfers Pi too easily
 only short term energy
ADP + Pi
storage
 carbohydrates & fats are A working muscle recycles over
long term energy storage 10 million ATPs per second
Whoa!
Pass me
the glucose
(and O2)!
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
loses e-
gains e-
+
oxidized
reduced
+
+
eoxidation
e-
–
ereduction
redox
Coupling oxidation & reduction
• REDOX reactions in respiration
– release energy as breakdown organic molecules
• break C-C bonds
• strip off electrons from C-H bonds by removing H atoms
– C6H12O6  CO2 = the fuel has been oxidized
• electrons attracted to more electronegative atoms
– in biology, the most electronegative atom?
– O2  H2O = oxygen has been reduced
O
– couple REDOX reactions &
2
use the released energy to synthesize ATP
oxidation
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
reduction
Oxidation & reduction
• Oxidation
• Reduction
– adding O
– removing H
– loss of electrons
– releases energy
– exergonic
– removing O
– adding H
– gain of electrons
– stores energy
– endergonic
oxidation
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
reduction
Moving electrons in respiration
• Electron carriers move electrons by
shuttling H atoms around
– NAD+  NADH (reduced)
– FAD+2  FADH2 (reduced)
NAD+
nicotinamide
Vitamin B3
niacin
O–
O–P –O
O
phosphates
O–
O–P –O
O
NADH
O
H
C
N+
+
adenine
ribose sugar
H H
NH2
C
reduction
O–
–
–O
oxidation O P
O
O–
O–P –O
O
carries electrons as
H
O
a reduced molecule
N+
NH
How efficient!
Build once,
use many ways
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. Citric Acid (Krebs) cycle
4. Electron transport chain
C6H12O6 +
6O2
 ATP + 6H2O + 6CO2 (+ heat)
Concept 9.2: Glycolysis harvests chemical
energy by oxidizing glucose to pyruvate
• Glycolysis (“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 occurs whether or not O2 is present
© 2011 Pearson Education, Inc.
Glycolysis
• Breaking down glucose
– “glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C
– 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
– occurs in cytosol
That’s not enough
ATP for me!
In the
cytosol?
Why does
that make
evolutionary
sense?
Evolutionary perspective
• Prokaryotes
– first cells had no organelles
Enzymes
of glycolysis are
“well-conserved”
• 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
You mean
we’re related?
Do I have to invite
them over for
the holidays?
endergonic
invest some ATP
exergonic
harvest a little
ATP & a little NADH
net yield
2 ATP
2 NADH
If you get bored……but you don’t
need to know this!!!
The Evolutionary Significance of Glycolysis
• Ancient prokaryotes are thought to have used
glycolysis long before there was oxygen in the
atmosphere
• Very little O2 was available in the atmosphere
until about 2.7 billion years ago, so early
prokaryotes likely used only glycolysis to
generate ATP
• Glycolysis is a very ancient process
© 2011 Pearson Education, Inc.
Concept 9.3: After pyruvate is oxidized, the
citric acid cycle completes the energyyielding oxidation of organic molecules
• In the presence of O2, pyruvate enters the
mitochondrion (in eukaryotic cells) where the
oxidation of glucose is completed
© 2011 Pearson Education, Inc.
The Citric Acid Cycle
• The citric acid cycle,
also called the Krebs
cycle, 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
© 2011 Pearson Education, Inc.
Figure 9.12-8
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
Energy accounting of Krebs cycle
4 NAD + 1 FAD
4 NADH + 1 FADH2
2x pyruvate          CO2
3C
3x 1C
1 ADP
1 ATP
ATP
Net gain = 2 ATP
= 8 NADH + 2 FADH2
Value of Krebs cycle?
• If the yield is only 2 ATP then how was the Krebs
cycle an adaptation?
– value of NADH & FADH2
• electron carriers & H carriers
– reduced molecules move electrons
– reduced molecules move H+ ions
• to be used in the Electron Transport Chain
like $$
in the
bank
There is a better way!
• Electron Transport Chain
– series of proteins built into
inner mitochondrial membrane
• along cristae
• transport proteins & enzymes
– transport of electrons down ETC linked to
pumping of H+ to create H+ gradient
– yields ~36 ATP from 1 glucose!
– only in presence of O2 (aerobic respiration)
That
sounds more
like it!
O2
Concept 9.4: During oxidative
phosphorylation, chemiosmosis couples
electron transport to ATP synthesis
• NADH and FADH2
account for most of
the energy extracted
from food
• They donate electrons
to the electron
transport chain,
• powers ATP synthesis
via oxidative
phosphorylation
© 2011 Pearson Education, Inc.
Mitochondria
• Double membrane
– outer membrane
– inner membrane
• highly folded cristae
• enzymes & transport
proteins
– intermembrane space
• fluid-filled space between
membranes
Oooooh!
Form fits
function!
Electrons flow downhill
• Electrons move in steps from
carrier to carrier downhill to oxygen
– each carrier (most are proteins – except
CoQ)more electronegative
– controlled oxidation (alternate red/ox)
– controlled release of energy
make ATP
instead of
fire!
Electron Transport Chain
Building proton gradient!
NADH  NAD+ + H
e
p
intermembrane
space
H+
H+
H  e- + H+
H+
C
e–
Q
e–
NADH H
FADH2
NAD+
NADH
dehydrogenase
inner
mitochondrial
membrane
e–
H
FAD
2H+ +
cytochrome
bc complex
1
O2
H 2O
2
cytochrome c
oxidase complex
mitochondrial
matrix
What powers the proton (H+) pumps?…
Stripping H from Electron Carriers
+
• Electron carriers pass electrons & H to ETC
– H cleaved off NADH & FADH2
– electrons stripped from H atoms  H+ (protons)
• electrons passed from one electron carrier to next in
mitochondrial membrane (ETC)
• flowing electrons = energy to do work
– transport proteins in membrane pump H+ (protons)
across inner membrane to intermembrane space
H+
+
H
H+
TA-DA!!
Moving electrons
do the work!
+
H
H+
+
H
H+
H+
+
H+ H+ H
+
H+ H H+
C
e–
NADH
Q
e–
FADH2
FAD
NAD+
NADH
dehydrogenase
e–
2H+
cytochrome
bc complex
+
1
H2O
2 O2
cytochrome c
oxidase complex
ADP
+ Pi
ATP
H+
But what “pulls” the
electrons down the ETC?
H2O
O2
electrons
flow downhill
to O2
oxidative phosphorylation
“proton-motive” force
We did it!
H+
H+
• Set up a H+
gradient
• Allow the protons
to flow through
ATP synthase
• Synthesizes ATP
ADP + Pi  ATP
Are we
there yet?
H+
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
Chemiosmosis
• The diffusion of ions across a membrane
– build up of proton gradient (also a pH gradient) just so
H+ could flow through ATP synthase enzyme to build
ATP
Chemiosmosis
links the Electron
Transport Chain
to ATP synthesis
So that’s
the point!
Pyruvate from
cytoplasm
Inner
+
mitochondrial H
membrane
H+
Intermembrane
space
Electron
transport
C system
Q
NADH
Acetyl-CoA
1. Electrons are harvested
and carried to the
transport system.
NADH
Krebs
cycle
e-
e-
FADH2
e-
2. Electrons
provide energy
to pump
protons across
the membrane.
e-
H2O
3. Oxygen joins
with protons to
form water.
1 O
2 +2
2H+
O2
H+
CO2
ATP
Mitochondrial
matrix
H+
ATP
ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
H+
ATP
synthase
• Oxidative phosphorylation accounts for almost
90% of the ATP generated by cellular
respiration (Energy stored in NADH and FADH2
is used to produce ATP)
© 2011 Pearson Education, Inc.
• A smaller amount of ATP is formed in glycolysis
and the citric acid cycle by substrate-level
phosphorylation
• For each molecule of glucose degraded to CO2
and water by respiration, the cell makes up to
32 molecules of ATP
© 2011 Pearson Education, Inc.
Cellular respiration
2 ATP
+
2 ATP
+
~36 ATP
Taking it beyond…
• What is the final
electron acceptor
O2
in Electron
Transport Chain?
H+
H+
H+
C
e–
NADH
Q
e–
FADH2
FAD
NAD+
NADH
dehydrogenase
e–
2H+ +
cytochrome
bc complex
1
H2O
2 O2
cytochrome c
oxidase complex
 So what happens if O2 unavailable?
 ETC backs up
nothing to pull electrons down chain
 NADH & FADH2 can’t unload H

 ATP production ceases
 cells run out of energy
 and you die!
An 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 ATP
© 2011 Pearson Education, Inc.
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
• Without O2, the electron
transport chain will cease to
operate
• In that case, glycolysis
couples with fermentation or
anaerobic respiration to
produce ATP
© 2011 Pearson Education, Inc.
Pyruvate is a branching point
Pyruvate
O2
O2
fermentation
anaerobic
respiration
mitochondria
Krebs cycle
aerobic respiration
AP Biology
Types of Fermentation
• Fermentation consists of glycolysis plus
reactions that regenerate NAD+, which can be
reused by glycolysis
• Two common types are alcohol fermentation
and lactic acid fermentation
© 2011 Pearson Education, Inc.
Alcohol Fermentation
pyruvate  ethanol + CO2
3C
NADH
2C
NAD+ back to glycolysis
 Dead end process
 at ~12% ethanol,
kills yeast
 can’t reverse the
reaction
Count the
carbons!
AP Biology
1C
bacteria
yeast
recycle
NADH
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
Lactic Acid Fermentation
pyruvate  lactic acid

3C
NADH
3C
NAD+ back to glycolysis
 Reversible process
 once O2 is available,
lactate is converted
back to pyruvate by
the liver
Count the
carbons!
AP Biology
O2
animals
some fungi
recycle
NADH
Figure 9.17b
2 ADP  2 P i
Glucose
2 ATP
Glycolysis
2 NAD 
2 NADH
 2 H
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
• In lactic acid fermentation, pyruvate is reduced
to NADH, forming lactate as an end product,
with no release of CO2
• Lactic acid fermentation by 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
© 2011 Pearson Education, Inc.
• Anaerobic respiration uses an electron
transport chain with a final electron acceptor
other than O2, for example sulfate
• Fermentation uses substrate-level
phosphorylation instead of an electron
transport chain to generate ATP
© 2011 Pearson Education, Inc.
Comparing Fermentation with Anaerobic
and 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
© 2011 Pearson Education, Inc.
• Obligate anaerobes carry out fermentation or
anaerobic respiration and cannot survive in the
presence of O2
• Yeast and many bacteria are facultative
anaerobes, meaning that they can survive
using either fermentation or cellular respiration
• In a facultative anaerobe, pyruvate is a fork in
the metabolic road that leads to two alternative
catabolic routes
© 2011 Pearson Education, Inc.
The Versatility of Catabolism
• Catabolic pathways funnel
electrons from many kinds
of organic molecules into
cellular respiration
• Glycolysis accepts a wide
range of carbohydrates
• Proteins must be digested
to amino acids; amino
groups can feed glycolysis
or the citric acid cycle
© 2011 Pearson Education, Inc.
• Fats are digested to
glycerol (used in glycolysis)
and fatty acids (used in
generating acetyl CoA)
• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Regulation of Cellular Respiration via
Feedback Mechanisms
• 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
• Control of catabolism is
based mainly on regulating
the activity of enzymes at
strategic points in the
catabolic pathway
© 2011 Pearson Education, Inc.
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