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Essential Idea
• Energy is converted to a usable form in cell respiration.
Understandings• Cell respiration involves the oxidation and reduction of electron
carriers.
• Phosphorylation of molecules makes them less stable.
• In glycolysis, glucose is converted to pyruvate in the cytoplasm.
• Glycolysis gives a small net gain of ATP without the use of oxygen.
• In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction.
• In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide.
• Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD.
• Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping.
Compare Oxidation vs. Reduction
Oxidation
• Lose electron
• Gain Oxygen
• Lose hydrogen
• Lose energy
• ATP is oxidized to ADP + P
• NADH is oxidized to NAD +H
Reduction
• Gain electron
• Lose oxygen
• Gain hydrogen
• Gain energy
• ADP is reduced to ATP
• NAD is reduced to NADH
IB Assessment Statement
• State that oxidation involves the loss of electrons from an element, and that oxidation frequently involves gaining oxygen or losing hydrogen,
• State that reduction involves a gain of electrons; reduction frequently involves losing oxygen or gaining hydrogen.
Oxidation
• Oxidation: often associated with the release of energy
Reduction
• Reduction: often associated with the gain of energy
Forms of Oxidation & Reduction
• In respiration the oxidation of organic compounds is coupled to the reduction of ADP to ATP.
• The oxidation of ATP is then coupled to biological processes such as muscle contraction of protein synthesis.
Ib Assessment Statement
• Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation. 2 In the cytoplasm, one hexose sugar is converted into two three-carbon atom compounds (pyruvate) with a net gain of two ATP and two NADH + H+.
The Stages of Cellular Respiration: A Preview
• Cellular respiration has three stages:
1. Glycolysis (breaks down glucose into two molecules of pyruvate)
2. The citric acid cycle/ Krebs Cycle (completes the breakdown of glucose)
3. Oxidative phosphorylation (accounts for most of the ATP synthesis)
• The latter process generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
Products of Glycolysis
• For every one molecule of glucose:
– 2 molecules of pyruvate are produced
– 2 ATP are produced
– 2 NAD+ are converted to NADH + H
Four Steps of Glycolysis
1. Phosphorylation
2. Lysis(splitting)
3. Oxidation
4. ATP formation
Glycolysis harvests energy by oxidizing glucose to pyruvate
• Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate
• Glycolysis occurs in the cytoplasm
• Requires NO oxygen and so is considered an Anaerobic Reaction
• The overall reaction for glycolysis is for every one molecule of glucose used:
– 2 molecules of Pyruvate are formed
– 2 net molecules of ATP are formed
– 2 molecules of NADH are formed
Understand Glycolysis:
• Glycolysis Animations
• http://tinyurl.com/yayelo9
• http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html
• http://www.iubmb-nicholson.org/swf/glycolysis.swf
There are four steps to the process of glycolysis
1. Phosphorylation
2. Lysis(splitting)
3. Oxidation
4. ATP formation
Steps of Glycolysis:
1. Phosphorylation – a reaction that uses 2 molecules of ATP molecules, and has three steps. First a phosphate group is added to glucose producing glucose phosphate.
– Phosphorylation of molecules makes them less stable.
Steps of Phosphorylation:
Second glucose phosphate is change to fructose phosphate
Steps of Phosphorylation:
Third another phosphate is added from ATP to fructose phosphate and changed to fructose diphosphate.
Steps of Glycolysis
Step 2 in glycolysis: Lysis (splitting)
The glucose molecule is split into two 3-carbon molecules called triose phosphate
Steps of Glycolysis
Step 3 in glycolysis: Oxidation of triose phosphate molecule. Removes a hydrogen and attaches the hydrogen to Nicotinamide adenine dinucleotide, NAD+ producing NADH and 2 new molecules called triose phosphate.
Steps of Glycolysis
Step 4 ATP Formation –
– Two triose phosphate molecules are converted to 2 pyruvate molecules
– Four ATP molecules are formed.
Net ATP gain in Glycolysis
• For every on molecule of Glucose used in glycolysis
– 2 molecules of ATP are use
– 4 molecules of ATP are formed
2 molecules of net ATP are made
Total Products of glycolysis
• For every one molecule of glucose:
– 2 molecules of pyruvate are produced
– 2 ATP are produced
– 2 NAD+ are converted to NADH + H
LE 9-8
Energy investment phase
Glucose
2 ATP used2 ADP + 2 P
4 ADP + 4 P 4 ATP formed
2 NAD+ + 4 e– + 4 H+
Energy payoff phase
+ 2 H+2 NADH
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
Net
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATPATPATP
Draw an annotated diagram of the process of glycolysis
Be sure to include/ label:
– 6 carbon sugar (glucose)
– Phosphorylation (adding 2 phosphates by via oxidation of ATP)
– Lysis – splitting the 6 Carbon sugar to 3 carbon sugars
– Add more phosphate to triose sugar
– Reduction of NAD+
– 4 ATP formation via reduction of ADP
– 2 three carbon pyruvate molecules
IB Assessment Statement
• Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs.
Krebs Cycle
Step 2 in cellular repiration: the Krebs cycle.
– The Krebs Cycle – Occurs in the mitochondria of cells
mitochondrion
animal cell
Structure of the mitochondria.
• Location of aerobic respiration
• Pyruvate, the product of glycolysis can be further oxidised here to release more energy.
• Mitochondria are only found in eukaryotic cells.
• Cells that need a lot of energy will have many mitochondria ( liver cell) or can develop them under training (muscles cells).
Structure of the mitochondria.
• There is a double membrane.
• The inner membrane is folded to form 'cristae'.
• There is a space between the two membranes which is important for creating a place to concentrate H+
• The inner space is called the matrix.
• Mitochondria contain some of their own DNA (mDNA).
IB Assessment Statement
• Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H+, the electron transport chain and the role of oxygen.
Stages in the Aerobic respiration:
• Link Reaction: Pyruvate is transported into the matrix of the mitochondria and is decarboxylated (loses CO2)
• Krebs cycle: carbon fragments (C2) are progressively decarboxylated to yield ATP and reduced coenzymes
• Electron Transport System: reduced coenzymes are used to generate more ATP (see 8.1.5).
Link Cycle to Krebs cycle
• The pyruvate from glycolysis diffuses into the matrix of the mitochondria.
• Before the Krebs cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis (LINK REACTION)
• Krebs cycle requires oxygen. So is considered an aerobic reaction.
LE 9-6_1
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
LE 9-6_2
Mitochondrion
Glycolysis
PyruvateGlucose
Cytoplasm
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Krebscycle
Link Reaction
CYTOPLASM
Pyruvate
NAD+
MITOCHONDRION
Transport protein
NADH + H+
Coenzyme ACO2
Acetyl Co A
Link Reaction: Pyruvate(3C) is transported to the matrix of the mitochondria
• A large Co-enzyme A joins with the 3 carbon fragment pyruvate.
• Pyruvate is decarboxylated removing a single carbon as carbon dioxide.
• The remaining carbon fragment is an Acetyl group and temporarily forms Acetyl CoA.
• NAD+ is reduced to NADH + H+.
• Acetyl (2C) is already transported into the matrix of mitochondria
Krebs Cycle Overview
•The Krebs cycle, takes place within the mitochondrial matrix
•The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn
Pyruvate(from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
NAD+
NADH
+ H+
CO2
CoA
Acetyl CoA
CoA
CoA
Calvincycle
CO22
3 NAD+
+ 3 H+
NADH3
ATP
ADP + P i
FADH2
FAD
Pyruvate(from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Oxidationphosphorylation
CitricacidcycleNAD+
NADH
+ H+
CO2
CoA
Acetyl CoACoA
CoA
Calvincycle CO2
2
3 NAD+
+ 3 H+
NADH3
ATP
ADP + P i
FADH2
FAD
Krebs Cycle Overview
•The krebs cycle has many steps, each catalyzed by a specific enzyme
•The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate
•The next several steps decompose the citrate back to oxaloacetate, making the process a cycle
•The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Calvincycle
CitrateIsocitrate
Oxaloacetate
Acetyl CoA
H2O
CO2
NAD+
NADH+ H+
-Ketoglutarate
CO2NAD+
NADH+ H+Succinyl
CoA
Succinate
GTPGDP
ADP
ATP
FAD
FADH2
Pi
Fumarate
H2O
Malate
NAD+
NADH+ H+
Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue
Step 1
•Acetyl CoA joins with the C4(acceptor)group (Oxaloacetate)
•CoA is released to transport more pyruvate into the matrix
•A C6 fragment is formed (citric acid)
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Krebscycle
Citrate
Isocitrate
Oxaloacetate
Acetyl CoA
H2O
Step 1
Acetyl CoA joins with the C4(acceptor)group (oxaloacetate)
CoA is released to transport more pyruvate into the matrix
A C6 fragment is formed (citric acid)
Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue
Step 2
•C6 (Citric Acid) is oxidatively decarboxylated.
•A C5 group is formed.
•The Carbon is given off as Carbon Dioxide
•NAD+ is reduced to NADH + H+
LE 9-12_2
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Citricacidcycle
Citrate
Isocitrate
Oxaloacetate
Acetyl CoA
H2O
CO2
NAD+
NADH
+ H+
-Ketoglutarate
CO2NAD+
NADH
+ H+SuccinylCoA
Step 2
C6 (Citric Acid) is oxidatively decarboxylated.
A C5 group is formed.
The Carbon is given off as Carbon Dioxide
NAD+ is reduced to
NADH + H+
Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue
Step 3
•The C5 fragment is oxidised and decarboxylated further to a C4 compound (-Ketoglutarate)
•Again the carbon removed forms carbon dioxide.
•NAD+ is further reduced to NADH + H+.
Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue
Step 4
•The final stage in the cycle has the C4 acceptor regenerated.
•There is a reduction of NAD+ to NADH + H+.
•FAD (Coenzyme)is reduced to FADH2 .
•ADP is reduced to ATP
LE 9-12_4
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Calvincycle
Citrate
Isocitrate
Oxaloacetate
Acetyl CoA
H2O
CO2
NAD+
NADH
+ H+
-Ketoglutarate
CO2NAD+
NADH
+ H+SuccinylCoA
Succinate
GTP GDP
ADP
ATP
FAD
FADH2
P i
Fumarate
H2O
Malate
NAD+
NADH
+ H+
Step 4
The final stage in the cycle has the C4 acceptor (oxaloacetate) regenerated.
There is a reduction of NAD+ to NADH + H+.
FAD (Coenzyme)is reduced to FADH2 .
ADP is reduced to ATP
Summarizing the Krebs Cycle for every one pyruvate molecule
• Two molecules of carbon dioxide are given off
• One molecule of ATP is formed
• Three molecules of NADH are formed
• One molecule of flavin adenine dinucleotide FADH are formed
• FADH and NADH carries electrons to the next step in respiration, the electron transport chain.
Krebs Cycle Summary
• (a) Pyruvate (3C)
• (b) Link reaction
• (c) C4 + C2= C6
• (d) Recycling of CoA
• (e) Decarboxylation C6 to C5 and the reduction of NAD
• (f) Decarboxylation C5 to C4 and the reduction of NAD
• (g) C4 to C4 with the reduction of coenzymes FAD and NAD. ATP is made directly.
• (h) C4 to C4 acceptor
• This cycle follows one acetyl group.
• Each glucose that enters glycolysis will produce 2 acetyl groups.
Krebs Cycle Animations
• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/krebsCycle.swf::krebsCycle.swf
• http://www.wiley.com/legacy/college/boyer/0470003790/animations/tca/tca.htm
• http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html
Krebs Cycle Resources & Help
• http://www2.nl.edu/jste/aerobic_respiration.htm
• http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html
Draw the Link Reaction & the Krebs Cycle
• Be sure to Label the C4 Molecule (oxaloacetate) in the beginning of the cycle and the end of the cycle
• Show one decarboxylation (loss of CO2) in the link reaction and the resulting 2 carbon molecule & reduction of NAD
• Show two decarboxylation (loss of CO2) in the kreb cycle reaction and show the resulting 5 and 4 carbon molecules
• Show the three reduction of NAD to NADH
• Show the one Reduction of FAD to FADH2
• Show the reduction of ADP to ATP
LE 9-6_3
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Citricacidcycle
ATP
Oxidativephosphorylation
Oxidativephosphorylation:electron transport
andchemiosmosis
Electronscarried
via NADH
Electrons carriedvia NADH and
FADH2
IB Assessment Statement
• Explain oxidative phosphorylation in terms of chemiosmosis.
During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
• Following glycolysis and the kreb cycle, NADH and FADH account for most of the energy extracted from food
• These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
NADH
50
FADH2
40 FMN
Fe•S
I FAD
Fe•S II
IIIQ
Fe•S
Cyt b
30
20
Cyt c
Cyt c1
Cyt a
Cyt a3
IV
10
0
Multiproteincomplexes
Fre
e en
erg
y (G
) re
lati
ve t
o O
2 (k
cal/m
ol)
H2O
O22 H+ + 1/2
Carrier Protiens
The electron transport chain is in the cristae (folds in the inner membrane of the mitochondrion)
Electron transport chain consist of proteins proteins called carriers imbedded in called carriers imbedded in the cristae.the cristae.
The carrier proteins alternate in accepting (being reduce) and donating (being oxidized) electrons
Electrons drop in energy as they go down the chain and are finally passed to O2, forming water
Oxidative Phosphorylation coupled to the synthesis of ATP.
•Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
•The NADH is oxidized and the reduced proteins transport H+ from the matrix into the space between both mitochondrial membranes.
•There is electron transfer down the chain of proteins in a series of oxidation and reductions.
•For each NADH, 3 Moles of H+ are pumped into the space.
Oxidative Phosphorylation coupled to the synthesis of ATP.
•The FADH2is oxidized and the reduced membrane proteins pump H+into the space between the mitochondrial membranes.
•One FADH2 produces two moles of hydrogen ions.
A concentration gradient has been created between the high concentration of H+ between the mitochondrial membranes and the lower concentration in the matrix.
• ATP synthetase is an enzyme embedded in the cristae membrane.
• H+create an electrochemical gradient (chemical potential energy).C
• The H+ pass through a channel in the enzyme driving the motor.
• The motor spins bringing together ADP and Pi to produce ATP
At the end of the Electron Transport Chain the electrons are given to oxygen. At the same time oxygen accepts hydrogen to form water.
Summary of Electron Transport Chain & Chemiosmosis
INTERMEMBRANE SPACE
H+ H+
H+H+
H+
H+
H+
H+
ATP
MITOCHONDRAL MATRIX
ADP+
Pi
A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient.
A stator anchored in the membrane holds the knob stationary.
A rod (or “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.
Summary of Chemiosmosis• Movement of
Hydrogen ions with its concentration gradient.
• These movement across the membrane protein ATP synthase provides energy needed to generate ATP.
LE 9-15
Protein complexof electroncarriers
H+
ATP ATP ATP
GlycolysisOxidative
phosphorylation:electron transportand chemiosmosis
Citricacidcycle
H+
Q
IIII
II
FADFADH2
+ H+NADH NAD+
(carrying electronsfrom food)
Innermitochondrialmembrane
Innermitochondrialmembrane
Mitochondrialmatrix
Intermembranespace
H+
H+
Cyt c
IV
2H+ + 1/2 O2 H2O
ADP +
H+
ATP
ATPsynthase
Electron transport chainElectron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
P i
ChemiosmosisATP synthesis powered by the flow
of H+ back across the membrane
Oxidative phosphorylation
Summary of Electron Transport Chain & ChemiosmosisSummary of Electron Transport Chain & Chemiosmosis
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 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP
Electron Transport & Chemiosmosis Animation
• http://www.stolaf.edu/people/giannini/flashanimat/metabolism/mido%20e%20transport.swf
• http://www.iubmb-nicholson.org/swf/ATPSynthase.swf
• 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
• http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn2.swf
• http://www.chem.purdue.edu/courses/chm333/oxidative_phosphorylation.swf
LE 9-16
CYTOSOL Electron shuttlesspan membrane 2 NADH
or
2 FADH2
MITOCHONDRION
Oxidativephosphorylation:electron transport
andchemiosmosis
2 FADH22 NADH 6 NADH
Citricacidcycle
2AcetylCoA
2 NADH
Glycolysis
Glucose2
Pyruvate
+ 2 ATP
by substrate-levelphosphorylation
+ 2 ATP
by substrate-levelphosphorylation
+ about 32 or 34 ATP
by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol
About36 or 38 ATPMaximum per glucose:
LE 9-18
Pyruvate
Glucose
CYTOSOL
No O2 presentFermentation
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
O2 present Cellular respiration
Citricacidcycle
LE 9-19
Citricacidcycle
Oxidativephosphorylation
Proteins
NH3
Aminoacids
Sugars
Carbohydrates
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
Fattyacids
Glycerol
Fats
• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
• A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
IB Assessment Statement
• Explain the relationship between the structure of the mitochondrion and its function.
Structure and function of the mitochondria.
8.1.6 Relationship between the structure and function of the mitochondria.
•1. Cristae folds increase the surface area for electron transfer system.
•2. The double membrane creates a small space into which the H+ can be concentrated.
•3. Matrix creates an isolated space in which the krebs cycle can occur.
Nature of Science
• Paradigm shift—the chemiosmotic theory led to a paradigm shift in the field of bioenergetics. (2.3)
Skills and Application
• Application: Electron tomography used to produce images of active mitochondria.
• Skill: Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur.
• Skill: Annotation of a diagram of a mitochondrion to indicate the adaptations to its function..