Post on 17-Jan-2016
Chapter 9 (Part 1): Chapter 9 (Part 1): Cellular RespirationCellular Respiration
AP BiologyMs. Gaynor
Energy Flows into ecosystems as sunlight and leaves as heat
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesisin chloroplasts
Cellular respirationin mitochondria
Organicmolecules
+ O2
ATP
powers most cellular work
Heatenergy http://wps.aw.com/bc_campbell_biology_7/
Carbon Cycle
Reminder…. AnabolicAnabolic pathways pathways (“(“A” A” for add together)for add together)
BuildBuild molecules from simpler ones (ex: molecules from simpler ones (ex: photosynthesis)photosynthesis)
Consume energy Consume energy ((endergonic)endergonic) CatabolicCatabolic pathways ( pathways (““C” C” for cut in parts)for cut in parts)
Break downBreak down complex molecules into complex molecules into simpler compounds (ex: cell respiration)simpler compounds (ex: cell respiration)
Release energy Release energy ((exergonic)exergonic)
Cellular respirationCellular respiration
Most efficient catabolic pathwayConsumes O2 and organic molecules (ex: glucose)
Yields ATP To keep working To keep working cells must regenerate ATPcells must regenerate ATP
Catabolic pathways yield energy by oxidizing organic fuels
The breakdown of organic molecules is exergonic
One catabolic process, fermentationfermentationIs a partial degradation of sugars that occurs without oxygen
Another example is cellular respirationcellular respiration
Cellular respirationCellular respirationOccurs in mitochondria
similar to combustion of gas in an engine after O2 is mixed with hydrocarbon fuel.Food = fuel for respiration. The exhaust =CO2 and H2O.
The overall process is:organic compounds + Oorganic compounds + O2 2 CO CO22 + H + H22O + energyO + energy
(ATP + heat)(ATP + heat)
Carbohydrates, fats, and proteins can all be used as the fuel, but most useful is glucose.
Mitochondria Mitochondria • # of mito’s in a cell varies by organism & tissue type
•has its own independent DNA (and ribosomes) this DNA shows similarity to bacterial DNA
•according to the endosymbiotic theory mitochondria (and chloroplasts) are descended from free-living prokaryotes.
Mitochondrion Structure
Mitochondrion Structure Outer membrane – similar to plasma
membrane; contains integral proteins Inner membrane- NOT permeable to
ions (needs help to cross); there is a membrane potential across the inner membrane; contains ATP synthase
Cristae – large surface area due to folding Matrix - gel-like in middle or lumen; many
contains enzymes for cellular respiration
RECALL…Redox ReactionsRECALL…Redox ReactionsCatabolic pathways yield energy
Due to the transfer of electrons Redox reactionsRedox reactions
Transfer e-’s from one reactant to another by oxidation and reduction In In ooxidationxidation
Substance lSubstance looses e-s (it’s oxidized)ses e-s (it’s oxidized) In In rreductioneduction
Substance Substance rreceives e-s eceives e-s (it’s reduced)(it’s reduced)
Examples of redox reactionsExamples of redox reactions
Na + Cl Na+ + Cl–
becomes oxidized(loses electron)
becomes reduced(gains electron)
Xe- + Y X + Ye-
**energy must be added to remove **energy must be added to remove e-e-
X = e- donor = X = e- donor = reducing agentreducing agent and reduces Y.and reduces Y.Y = e- recipient = Y = e- recipient = oxidizing agentoxidizing agent and oxidizes X.and oxidizes X.
Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respirationGlucose is oxidized oxygen is reducedE-’s lose potential energy energy is released
CC66HH1212OO66 + 6 + 6OO22 6 6COCO22 + 6 + 6HH22OO + Energy + Energybecomes oxidizedbecomes oxidized
becomes reducedbecomes reduced
http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/ets_flash.html
Electrons are not transferred directly to oxygen but are passed first to a coenzyme called NAD+ or FADNAD+ or FAD
NAD+
HO
OO O–
OO O–
O
O
O
P
P
CH2
CH2
HO OHH
HHO OH
HO
H
H
N+
C NH2
HN
H
NH2
N
N
Nicotinamide(oxidized form)
NH2+ 2[H]
(from food)
Dehydrogenase
Reduction of NAD+
Oxidation of NADH
2 e– + 2 H+
2 e– + H+
NADH
OH H
N
C +
Nicotinamide(reduced form)
N
Figure 9.4
NAD+ and FADNAD+ and FAD= = e- acceptor and e- acceptor and oxidating agentoxidating agent
2 H 1/2 O2
(from food via NADH)(from food via NADH)
2 H+ + 2 e–
2 H+
2 e–
H2O
1/2 O2
Controlled Controlled release of energy release of energy
for for synthesis ofsynthesis of
ATPATP ATP
ATP
ATP
Electro
n tran
spo
rt chain
Fre
e en
ergy
, G
(b) Cellular respiration
+
Electron Flow =food NADH/FADH2 ETC oxygen
The Stages of Cellular Respiration
Respiration is a cumulative process of 3 metabolic stages
1. Glycolysis2. The citric acid cycle3. Oxidative phosphorylation
The 3 StagesThe 3 Stages GlycolysisGlycolysis
Breaks down glucose into 2 molecules of pyruvate
Makes NADH Kreb’s Cycle (Citric acid cycle)Kreb’s Cycle (Citric acid cycle)
Completes the breakdown of glucoseMakes NADH and FADH2
Oxidative phosphorylationOxidative phosphorylationDriven by the electron transport chainGenerates ATP
An overview of cellular respiration
Figure 9.6
ElectronsElectronscarriedcarried
via NADHvia NADH
GlycolsisGlycolsisGlucoseGlucose 2 Pyruvate2 Pyruvate
ATP
Substrate-levelphosphorylation
Electrons carried Electrons carried via NADH and via NADH and
FADHFADH22
Citric Citric acid acid cyclecycle
OxidativeOxidativephosphorylation:phosphorylation:
electron electron transport andtransport and
chemiosmosischemiosmosis
ATPATP
Substrate-levelphosphorylation
Oxidativephosphorylation
Mitochondrion MatrixMitochondrion MatrixCytoplasmCytoplasm
Inner Mitochondrion Membrane Inner Mitochondrion Membrane (Cristae)(Cristae)
Both glycolysis and the citric acid cycleCan generate ATP by substrate-level
phosphorylation (not using ATP synthase!)
Figure 9.7
Enzyme Enzyme
ATP
ADP
Product
SubstrateP
+
Stage #1: GlycolysisStage #1: Glycolysis Glycolysis produces energy by oxidizing
glucose pyruvate Glycolysis
Means “splitting of sugar”Breaks down glucose into pyruvateOccurs in the cytoplasmcytoplasm of the cell
1 glucose breaks down 4 ATP made + 2 pyruvate molecules
(net gain of 2 ATP…NOT 4 ATP)
Glycolysis consists of two major phases1. Energy
investment phase (endergonic= uses 2 ATP)
2. Energy payoff phase
(exogonic = makes 4 ATP)
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATP ATP ATP
2 ATP
4 ATP
used
formed
1 Glucose
2 ADP + 2 P
4 ADP + 4 P
2 NAD2 NAD++ + 4 + 4 ee-- + 4 H + 4 H ++
2 NADH
+ 2 H+
2 Pyruvate + 2 H2 Pyruvate + 2 H22OO
Energy investment phaseEnergy investment phase
Energy payoff phase
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H + 2 NADH
+ 2 H+
Glycolysis
NETNET Glucose Glucose 2 pyruvate (pyruvic 2 pyruvate (pyruvic acid) acid) + 2 H+ 2 H22OO
4 ATP formed – 2 ATP used 4 ATP formed – 2 ATP used 2 ATP 2 ATP GAINGAINsubstrate-level phosphorylation usedsubstrate-level phosphorylation used
2 NAD+ + 4e- + 4H+ 2 NAD+ + 4e- + 4H+ 2 NADH + 2H+ 2 NADH + 2H+
**Glycolysis can proceed WITHOUT O**Glycolysis can proceed WITHOUT O22
The energy investment & The energy investment & Payoff phases of Payoff phases of
GlycolysisGlycolysisLet’s take a closer look….
Page 166-167 in textbook10 steps in glycolysis occuring in 2 phases
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
H H
H
HH
OH
OH
HOHO
CH2OH
H H
H
HO H
OHHO
OH
P
CH2O P
H
OH
HO
HO
HHO
CH2OH
P O CH2 O CH2 O P
HO
HHO
HOH
OP CH2
C O
CH2OH
H
C
CHOH
CH2
O
O P
ATP
ADPHexokinase
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
ATP
ADP
Phosphoglucoisomerase
Phosphofructokinase
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Glycolysis
1
2
3
4
5
CH2OH
Oxidativephosphorylation
Citricacidcycle
Phase #1: The
Investment Phase of
Glycolysis
(endergonic)
2 NAD+
NADH2
+ 2 H+
Triose phosphatedehydrogenase
2 P i
2P C
CHOH
O
P
O
CH2 O
2 O–
1, 3-Bisphosphoglycerate2 ADP
2 ATPPhosphoglycerokinase (PFK)
CH2 O P
2
C
CHOH
3-Phosphoglycerate
Phosphoglyceromutase
O–
C
C
CH2OH
H O P
2-Phosphoglycerate
2 H2O
2 O–
Enolase
C
C
O
PO
CH2
Phosphoenolpyruvate2 ADP
2 ATP
Pyruvate kinase
O–
C
C
O
O
CH3
2
6
8
7
9
10
Pyruvate
O
Phase #2: The Payoff Phase of
Glycolysis (exogonic)
Phosphofructoskinase (PFK)
• is an allosteric enzyme
•ATP acts as an allosteric inhibitor to PFK
•High [ATP] stops glycolysis via inhibition (blocks active site)
Glycolysis http://www.sumanasinc.com/webcontent/animations/content/cellular
respiration.html
http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html
http://www.northland.cc.mn.us/biology/Biology1111/animations/glycolysis.html
http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html
Stage #2: The Kreb’s Cycle
The citric acid cycleTakes place in the matrix of the
mitochondrion
**NEEDS O2 TO PROCEED (unlike glycolysis)
Stage #1 ½ : The Citric Acid Cycle Before the citric acid cycle can begin
Pyruvate must first be converted to acetyl CoA, which links the citric acid cycle to glycolysis
CYTOSOL MITOCHONDRION
NADH + H+NAD+
2
31
CO2
Coenzyme Coenzyme A A
(a vitamin)(a vitamin)Pyruvate
Acetyle Acetyle CoACoA
S CoA
C
CH3
O
Transport Transport proteinprotein
O–
O
O
C
C
CH3
Figure 9.10
Uses active
transport
Diffuses out of cell
Acetyl group= unstable
The Kreb’s Cycle
Also called the “Tricarboxylic Acid Cycle” or the “Citric Acid cycle”
NAD+ and FAD (both are coenzymes) = electron “carriers”; proton acceptorsThey are reduced and carry e-’s from
Citric cycle to ETCDehydrogenase catalyzes hydrogen
transfer reaction
NAD+ and FADOxidized Form Reduced Form NAD+ NADH (2 e-, 1 H)
FAD FADH2 (4 e-, 2 H)
THINK: FADH2 come into play in the 2nd stage of cellular respiration; it is also the 2nd electron carrier
An overview An overview of the citric of the citric acid cycleacid cycle
(this occurs (this occurs for EACH for EACH pyruvate pyruvate molecule)molecule)
ATP
2 CO2
3 NAD+
3 NADH+ 3 H+
ADP + P i
FAD
FADH2
Citricacidcycle
CoA
CoA Acetyle CoA
NADH+ 3 H+
CoA
CO2
Pyruvate (from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Citricacidcycle
Oxidativephosphorylation
Figure 9.11
The Kreb’s CycleThe Kreb’s CycleLet’s take a closer look….
Page 169 in textbook8 steps in citric cycle in MATRIX1 turn of cycle 2 reduced carbons enter 2 oxidized carbons leave
Figure 9.12
Acetyl CoA
NADH
Oxaloacetate
CitrateMalate
Fumarate
Succinate
SuccinylCoA
-Ketoglutarate
Isocitrate
Citricacidcycle
S CoA
CoA SH
NADH
NADH
FADH2
FAD
GTP GDP
NAD+
ADP
P i
NAD+
CO2
CO2
CoA SH
CoA SH
CoAS
H2O
+ H+
+ H+ H2O
C
CH3
O
O C COO–
CH2
COO–
COO–
CH2
HO C COO–
CH2
COO–
COO–
COO–
CH2
HC COO–
HO CH
COO–
CH
CH2
COO–
HO
COO–
CH
HC
COO–
COO–
CH2
CH2
COO–
COO–
CH2
CH2
C O
COO–
CH2
CH2
C O
COO–
1
2
3
4
5
6
7
8
Glycolysis Oxidativephosphorylation
NAD+
+ H+
ATP
Citricacidcycle
Figure 9.12
Kreb’s Cycle Summary pyruvate Acetyl-CoA + 1 NADH Each turn of cycle uses 1 pyruvate
So… 1 glucose molecule produces 2 turns of Kreb’s cycle
1 turn of cycle yields 4 NADH, 1 ATP, and 1 FADH2 and 3 CO2 (as waste product) Remember to multiply by 2…why?
http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html
Http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html
Stage #3: Oxidative Phosphorylation
(Electron Transport Chain (ETC) + Chemiosmosis) Chemiosmosis couples electron
transport to ATP synthesis NADH and FADH2
Donate e-s to ETC, which powers ATP synthesis using oxidative phosphorylation
**OCUURS IN CRISTAE (folds of inner membrane)
What is “oxidative phosphorylation”?
Recall…Take H+/e-s away, molecule = “oxidized” Give H+/e-s, molecule = “reduced” Give phosphate, molecule =
“phosphorylated” So…oxidative phosphorylation =
process that couples removal of H+’s/ e-’s from one molecule & giving phosphate molecules to another molecule
The Pathway of Electron Transport
In the ETC…e-s from NADH and FADH2 lose energy in several steps
**NEEDS O2 TO PROCEED
(unlike glycolysis)
ETC Characteristics
Lots of proteins (cytochromes) in cristae increases surface area1000’s (many) copies of ETC
ETC carries e-’s from NADH/FADH2 O2
O2 = pulls e-s “down” ETC due to electronegativity (high affinity for e-s)
Chemiosmosis and the electron transport chain
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+
H+
H+
H+
ATPP i
Protein complexof electron carriers
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesis
Protin motive force
is used!
At the end of the chainElectrons are passed to oxygen, forming waterO2 = final e- acceptor
NAD delivers e- higher than FAD NAD provides 50% more ATP
What happens at the end of the ETC chain?
ETC is a Proton (H+) Pump Uses the energy from “falling” e-s
(exergonic flow) to pump H+’s from matrix to outer compartment
A H+ (proton) gradient forms inside mitochondria
ETC does NOT make ATP directly but provides stage for CHEMIOSOMOSIS to occur
RECALL…ChemiosmosisRECALL…Chemiosmosis Is an energy-coupling mechanism that uses energy in the
form of a H+ gradient across a membrane to drive cellular work
Uses ATP synthaseMakes ~90% of ATP in Cell Resp. Proposed by Peter Mitchell (1961)
Chemiosmosis: The Energy-Coupling Mechanism
ATP synthase Is the enzyme
that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+ H+
H+
P i
+ADP
ATP
A rotor within the membrane spins clockwise whenH+ flows past it down the H+
gradient.
A protein anchoredin the membraneholds the knobstationary.
A rod (or “stalk”)extending into the rotor/ knob alsospins, activatingcatalytic sites inthe knob.
Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP.
MITOCHONDRIAL MATRIXFigure 9.14
http://www.sigmaaldrich.com/life-science/metabolomics/learning-center/metabolic-pathways/atp-synthase.html
A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
Chloroplasts and mitochondriaGenerate ATP by the SAME basic
mechanism: chemiosmosisBut use different sources of energy to
accomplish this http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/
atpase_flash.html
The spatial organization of chemiosmosisDiffers in chloroplasts
and mitochondria In both organelles
electron transport chains generate a H+ gradient across a membrane
ATP synthase Uses this proton-motive
force to make ATP
At certain steps along the ETCElectron transfer causes protein complexes
to pump H+ from the mitochondrial matrix intermembrane spaceInside (matrix) = low [H+]Outside = high [H+]
The resulting H+ gradient…Stores energyDrives chemiosmosis in ATP
synthaseIs referred to as a proton-motive force
There are three main processes in this metabolic enterprise
Electron shuttlesspan membrane
CYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose
2Pyruvate
2AcetylCoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
MITOCHONDRION
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidative phosphorylation
Maximum per Maximum per glucose:glucose:
AboutAbout36 or 38 ATP36 or 38 ATP
+ 2 ATP + about 32 or 34 ATP
or
Figure 9.16
+ 2 ATP
About 40% of the energy in a glucose moleculeIs transferred to ATP during cellular respiration, making ~36- 38 ATP
http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html
Overall (Aerobic Respiration) FADH
2NADH CO2 ATP Total ATP
Gained
Glycolysis2 4 2 (net)
PyruvatePyruvate Acetyl- Acetyl-
CoACoA
2
Kreb’sCycle
2 6 6 2 2
ETC~32-34
ATP GRAND TOTAL = ~36-38 ATP per 1 GLUCOSEATP GRAND TOTAL = ~36-38 ATP per 1 GLUCOSE
Chapter 9 (Part 2): Chapter 9 (Part 2): FermentationFermentation
AP BiologyMs. Gaynor
Fermentation Fermentation enables some cells to
produce ATP without the use of oxygen (O2)
Cellular respirationRelies on oxygen to produce ATP
In the absence of oxygenCells can still produce ATP
through fermentation
GlycolysisCan produce ATP with or without oxygen, in aerobic or anaerobic conditions
Couples with fermentation to produce ATP
Types of Fermentation
Fermentation consists ofGlycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis
Alcohol Fermentation
Pyruvate is converted to ethanol (ethyl alcohol) in two steps, one of which releases CO2
Ex: bacteria and yeast
In alcohol fermentationPyruvate is converted to ethanol (ethyl alcohol) in two steps, one of which releases CO2
GLUCOSE Pyruvate Ethanol and CO2
Ex: bacteria and yeast do this
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Pyruvate
2 Acetaldehyde (gets reduced by NADH. It is the
oxidizing agent.)
2 Ethanol(a) Alcohol fermentation
H
H OH
CH3
C
O –
OC
C O
CH3
H
C O
CH3
CO22
Lactic Acid FermentationDuring lactic acid fermentation
Pyruvate is reduced directly to NADH to form lactate as a waste product
NO CO2 is releasedEx #1: fungus and bacteria in dairy industry to make cheese/ yogurtEx #2: Human muscle cells
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH2 Pyruvate
2 Acetaldehyde (gets reduced by NADH. It
is the oxidizing agent.)
2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Lactate
(b) Lactic acid fermentation
H
H OH
CH3
C
O –
OC
C O
CH3
H
C O
CH3
O–
C O
C O
CH3O
C O
C OHH
CH3
CO22
NO CO2
made 2 Pyruvate (gets reduced by NADH. It
is the oxidizing agent.)
Fermentation and Cellular Respiration Compared
Both fermentation and cellular respirationUse glycolysis to oxidize glucose and
other organic fuels to pyruvate
Fermentation and cellular respirationDiffer in their final electron acceptor
Cell respriraition uses O2
Fermentation uses NAD+ Cellular respiration
Produces more ATP (~36-38 ATP) Fermentation
Produces 2 ATP per cycle
Pyruvate is a key juncture in catabolismGlucose
CYTOSOL
PyruvateNo O2 presentFermentation
OO22 present present
Cellular respirationCellular respiration
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
Citricacidcycle
Figure 9.18
The Evolutionary Significance of Glycolysis
GlycolysisOccurs in nearly all organismsProbably evolved in ancient prokaryotes
before there was oxygen in the atmosphereO2 in air ~2.7 bya; oldest prokaryotes ~3.5 byaAlso does not require organelles
The catabolism of various molecules from food called “intermediates”
Amino acids
Sugars Glycerol Fattyacids
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citricacidcycle
Oxidativephosphorylation
FatsProteins Carbohydrates
Figure 9.19
The control of cellular respiration through feedback inhibition PFK is an allosteric
enzyme
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphateInhibits Inhibits
Pyruvate
ATPAcetyl CoA
Citricacidcycle
Citrate
Oxidativephosphorylation
Stimulates
AMP
+
– –
Figure 9.20
Excellent Overall Tutorial of Cell Respiration
http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html