Transcript RACC BIO Cellular respiration

Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
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• Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside
sources to perform their many tasks
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Chemical Cycling System
• Energy
– Flows into an ecosystem as sunlight and
Light energy
leaves as heat
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
CD rom activity
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Heat
energy
• Concept 9.1: Catabolic pathways yield energy
by oxidizing organic fuels
• Catabolic –release energy stored in
molecules
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Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is
exergonic
• Exergonic – release of free energy,
happens spontaneously
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2 catabolic process during respiration
• fermentation (no oxygen present)
• Cellular respiration (oxygen present)
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C6H12O6 + 6 O2
6 CO2 + 6 H2O + Energy
• Cellular respiration
– Is the most prevalent and efficient catabolic
pathway
– Consumes oxygen and organic molecules
such as glucose
– Yields ATP
• ATP is regenerated to keep cells working
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• Catabolic pathways yield energy
– Due to the transfer of electrons
• This transfer takes place by Redox Reactions:
– Oxidation and Reduction
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• If electron transfer is not stepwise
– A large release of energy occurs
– As in the reaction of hydrogen and oxygen to
form water
If cellular respiration took place
in one step, all of the energy
from glucose would be released
at once, most of it would be in
the form of heat and light.
A living cell doesn’t want to just
start a fire, it has to release the
energy a little at a time.
Figure 9.5 A
Free energy, G
H2 + 1/2 O2
Explosive
release of
heat and light
energy
H2O
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(a) Uncontrolled reaction
We will see later that…
• The electron transport chain
– Passes electrons in a series of steps instead of
in one explosive reaction
– Uses the energy from the electron transfer to
form ATP
• What are redox reactions?
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The Principle of Redox
• Redox reactions
– Transfer electrons from one reactant to
another by oxidation and reduction
– Oxidations and reductions always go together
since electrons are passed from one molecule
to another.
– Oxidation is the observation that all elements
react with oxygen to form oxides.
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• In oxidation
– A substance loses electrons, or is oxidized
• Loss of Electrons is Oxidation
LEO
• In reduction
– A substance gains electrons, or is reduced
• Gain of Electrons is Reduction
GER
LEO says GER
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• Examples of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
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Cl–
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
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The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three
metabolic stages
– Glycolysis
– The citric acid cycle OR Krebs Cycle
– Oxidative phosphorylation
• The Electron Transport Chain
– Preview biofilms
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The Major “Players” in oxidizing glucose
• Enzymes called dehydrogenase and
Coenzymes
– Coenzymes are organic molecules that bind to
an enzyme, helping with its catalytic function
• Coenzyme NAD+ (nicotinamide adenine dinucleotide)
– An organic molecule cells make from the vitamin
niacin
– Used to shuttle electrons
.
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What they do
• Dehydrogenase strips 2 hydrogen atoms from
glucose
– (H carries 2 electrons)
• NAD+ picks up the two electrons and is
reduced to NADH
– NADH delivers the electrons to the electron
transport chain
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Cellular Respiration
• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Electron
Transport Train
Krebs
Mitochondrion
ATP
Figure 9.6
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ATP
ATP
Glycolysis- Occurs In the Cytoplasm of the Cell
• Glycolysis harvests energy by oxidizing
glucose to pyruvate
• Glycolysis
–
Means “splitting of sugar”
•
–
Glyco “sweet” and lysis “split”
Breaks down glucose into pyruvate
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Glycolysis
• Glycolysis occurs universally (all living
organisms)
• It does not require oxygen
• It does not occur inside a membrane bound
organelle
• Thought to be a very ancient system
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Glycolysis
• Glycolysis consists of two major phases
– Energy input
Citric
acid
cycle
Glycolysis
– Energy output
Oxidative
phosphorylation
ATP
ATP
ATP
Energy investment phase
Glucose
2 ATP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H
+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
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2 NAD+ + 4 e– + 4 H
+
2 Pyruvate + 2 H2O
2 ATP + 2 H+
2 NADH
Glycolysis
4 molecules of ATP are produced by glycolysis, but since the
preparatory step used 2 ATP molecules to start the
NET GAIN to the cell is
2 molecules of ATP (for each glucose)
2 NADH
2 pyruvate
Complete first part of foldout
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The Citric Acid Cycle
• The citric acid cycle completes the energyyielding oxidation of organic molecules
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
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Citric Acid Cycle
•
Before the citric acid cycle can begin
–
Pyruvate must first be converted to acetyl CoA, which links the
cycle to glycolysis (this is a high energy fuel molecule)
1. A carbon atom is removed from
pyruvate and released in CO2
2. The two-C compound remaining is
oxidized while a molecule of NAD+ is
reduced to NADH
CYTOSOL
NAD+
NADH
O–
MITOCHONDRION
+
H+
S
C
oA
C
O
2
C
3. A compound called coenzyme A
(derived from a B vitamin), joins with the
two-C group to form a molecule called
acetyl coenzyme A
Electrons are
removed changing
NAD+ to NADH
C
O
O
1
3
CH3
Pyruvate
Transport protein
For each molecule of glucose that
Entered glycolysis, two molecules of acetyl CoA are
produced and enter the citric acid cycle
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CO2
Coenzym
eA
CH3
Acetyle
CoA
Citric Acid Cycle: AKA – The Krebs Cycle
• An overview of the Citric acid cycle
Pyruvate
(from glycolysis,
2 molecules per glucose)
This will cycle twice
because 2 pyruvate
molecules are
formed during
glycolysis
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
Only the two-carbon acetyl part enters the
cycle. Coenzyme A helps the acetyl group
enter. It is then split off and recycled
CoA
Three NADH and one
FADH2 are formed. These
will be used to generate
energy in the form of ATP
later.
Citric
acid
cycle
3 NAD+
FADH2
One ATP is formed by substratelevel phosphorylation. This can be
used directly for cellular activities.
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
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2 CO2
Two carbons enter
in the reduced
form from acetyl
CoA and two
carbons exit,
completely
oxidized as CO2.
This is the carbon
dioxide you
exhale.
Substrate level phosphorylation
• Directly adding a phosphate onto ADP to
produce ATP
• Takes place during glycolysis and Krebs cycle
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Krebs Cycle
• Complete Citric Acid Cycle foldout
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The Pathway of Electron Transport – Electrons from NADH and FADH2 lose
energy in several steps – Oxydative Phosphorylation is simply the transfer of electrons from NADH and FADH to O2
•
The electron transport chain – takes place in the cristae (infoldings of the inner
mitochondrial membrane)
•
It functions as a chemical machine
–
Uses energy released by the “fall” of electrons to pump hydrogen ions (H+)
across the inner mitochondrial membrane
–
They store energy as they become more concentrated on one side of the
membrane
2H
1/
+
2
O2
Free energy, G
2 H+ + 2 e–
ATP
ATP
ATP
2
e–
2 H+
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1/
2
O2
H2O
Electron Transport
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
2. Electron transport chains use
this energy to pump H+ across the
inner membrane of the
mitochondria
ATP
4.H+ ions flow back
through an ATP
synthase. This spins
a part of the synthase.
H+
H+
H+
Intermembrane
space
Inner
mitochondrial
membrane
H+
Protein complex
of electron
carners
FADH2
FAD+
Figure 9.15
H2O
5.The ATP
synthase
NAD+
ATP uses the
+ Pi
1.NADH transfers electrons
energy of
From food to electron
H+
the H+
Transport chains
gradient
Chemiosmosis
Electron transport chain
to
Electron transport and pumping of protons (H+), ATP synthesis powered by the flowregenerate
which create an H+ gradient across the membrane Of H+ back across the membrane ATP from
ADP
Oxidative phosphorylation
NADH+
Mitochondrial
matrix
2 H+ + 1/2 O2
ATP
synthase
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3. Oxygen functions
to Pull electronsADP
down the transport
chain.
Electron Transport
• The hydrogen ions will eventually gush back to
where they are less concentrated.
• The membrane temporarily restrains the H+
ions
– (like a dam holding back water)
www2.nl.edu/jste/electron_transport_system.htm
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Chemiosmosis: The Energy-Coupling Mechanism
•
The energy of the H+ ions is generated like water in a dam. As it
gushes through turbines that spin to create electricity , or in this case,
energy.
•
ATP synthase is the enzyme that actually makes ATP
INTERMEMBRANE SPACE
It acts like the turbine in the
mitochondria.
H+
H+
H+
H+
Chemiosmosis
H+
is the movement of ions across
a selectively permeable
membrane, down their
electrochemical gradient. More
specifically, it relates to the
generation of ATP by the
movement of hydrogen ions
across a membrane during
cellular respiration or
photosynthesis.
H+
H+
H+
ADP
+
Pi
Figure 9.14
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MITOCHONDRIAL
MATRIX
ATP
A rotor within
the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
A stator anchored
in the membrane
holds the knob
stationary.
A rod (for “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
Three catalytic
sites in the
stationary knob
join inorganic
Phosphate to ADP
to make ATP.
Electron Transport Chain
• The resulting H+ gradient
– Stores energy
– Drives chemiosmosis in ATP synthase
– Is referred to as a proton-motive force
• Because some members of the chain that
pass electrons also accept and release
protons.
• Protons are stored in the intermembrane
space and are used to synthesize ATP.
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• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Enzyme
transfers a
phosphate
group from a
substrate to ATP
ADP to make
ATP
Substrate-level
phosphorylation
re 9.6
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Mitochondrion
ATP
Substrate-level
phosphorylation
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ATP
Oxidative
phosphorylation
Redox
reactions
are used
to
synthsize
ATP
An Accounting of ATP Production by Cellular
Respiration
• During respiration, most energy flows in this
sequence
– Glucose to NADH to electron transport chain to
proton-motive force to ATP
– Each NADH is worth 3 ATP’s
– Each FADH is worth 2 ATP’s
– There are also the ATP’s produced directly
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Energy Production
• About 40% of the energy in a glucose molecule
– Is transferred to ATP during cellular
respiration, making approximately 38 ATP
Process
Direct ATP
NADH
Glycolysis
2
2
Pyruvate to
acetyl CoA
Citric Acid 2
2
6
2
Total ATP
30
4
4
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FADH
Fermentation
• Fermentation enables some cells to produce
ATP without the use of oxygen
• Cellular respiration
– Relies on oxygen to produce ATP
• In the absence of oxygen
– Cells can still produce ATP through
fermentation
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Fermentation
• Glycolysis
– Can produce ATP with or without oxygen, in
aerobic (with) or anaerobic (without) conditions
– Couples with fermentation to produce 2 net
ATP
– The problem is recycling the electron acceptor
NAD+
–
During cellular respiration, the electron transport train will recycle NADH
to NAD+ when it gives up its electrons. This will not occur when oxygen
isn’t present
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Fermentation
• Fermentation allows recycling of NAD+ from
NADH
• Glycolysis can continue and small amounts of
ATP can be generated
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Fermentation in Human Muscle Cells
• During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form
lactate as a waste product
–
This will occur if your muscles must spend ATP at a rate that
outpaces the delivery by the bloodstream of oxygen from your
lungs to your muscles.
–
An example is when you are doing a “hard work out”
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Lactic Acid Fermentation (the bottom picture)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
P1
2 ATP
2 ADP + 2
O–
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
C O
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
C O
Glucose
Glycolysis
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
CH3
2 Pyruvate
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
2 NADH
2 NAD+
H
H C OH
CH3
2 Ethanol
(a) Alcohol fermentation
2 ADP + 2
Glucose
Figure 9.17
P1
2 CO2
H
C O
CH3
2 Acetaldehyde
‘
2 ATP
Glycolysis
2 NADH
2 NAD+
O
C O
H C OH
CH3
2 Lactate
(b) Lactic acid fermentation
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O–
C O
C O
CH3
NAD+ must be present as an
electron acceptor during
glycolysis. And with oxygen
present the cell can regenerate its
NAD+ when NADH drops its
electron cargo down electron
transport chains to oxygen.
This cannot happen without
oxygen present.
Instead, NADH disposes of
electrons by adding them to the
pyruvic acid produced by
glycolysis.
This restores NAD+ and keeps
glycolysis working as an ATP
source.
Reduction of pyruvic acid
produces a waste product called
lactic acid.
Fermentation in Microorganisms
• In alcohol fermentation
– Occurs in yeast
– Ethyl alcohol is produced as a waste product
along with CO2
– Pyruvate is converted to ethanol in two steps,
one of which releases CO2
• See next slide
some bacteria and fungi produce lactic acid as their waste. This is
used to flavor milk and cheese.
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Alcohol Fermentation
.
.
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Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
• NAD+ is the oxidizing agent
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• Fermentation and cellular respiration
– Differ in their final electron acceptor
– Fermentation uses pyruvate or acetaldehyde
as the final electron acceptor
– Respiration uses oxygen, via electron trasport
• Cellular respiration
– Produces more ATP
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•
Pyruvate is a key juncture in catabolism (release energy – break down)
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
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Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes before
there was oxygen in the atmosphere
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• Concept 9.6: Glycolysis and the citric acid
cycle connect to many other metabolic
pathways
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The Versatility of Catabolism
• Catabolic pathways
– Funnel electrons from many kinds of organic
molecules into cellular respiration
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• The catabolism of various molecules from food. All are
used to make ATP via cellular respiration
Proteins are
digested into
amino acids,
which can enter
into respiration at
several sites.
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
Oxidative
phosphorylation
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Fatty
acids
Digestion of fats
yields glycerol,
which is converted
to an intermediate
of glycolysis, and
fatty acids, which
are broken down
to 2 carbon
fragments that
enter the citric acid
cycle as acetyl
CoA