Download Chapter 9: Cellular Respiration 1 Photosynthesis and Respiration

Chapter 9: Cellular Respiration
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Figure 9.1 Energy flow and chemical recycling in ecosystems
Photosynthesis and Respiration—cyclic flow
• Recycle CO2, H2O, O2, organic materials
• Light Energy in
• Heat Energy out
Energy stored in arrangement of atoms (glucose and ATP)
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Summary of Processes
3 See Figure 9.2
ATP stores energy, allows work to be done
• Transport
• Mechanical
• Chemical
Phosphorylation change conformation or reactivity
ATP ADP + Pi
• Phosphate (not phosphorus)
• i = inorganic
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Cellular Respiration
• C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP)
• ∆G = -686 kcal/mol (-2870 kJ/mol)
Catabolic
Similar to combustion
• Can release energy all at once (heat) OR. . ..
• Enzymes systematically degrade organic material, store energy
• Energy can be released:
– All at one time: Combustion
– Slowly through several controlled steps: Respiration
Goalgenerate ATP from ADP (muscle 10 million/sec)
Can use fat, protein, other carbs for energy, but will focus on glucose.
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Oxidation Reduction Reactions
• Redox Reactions: transfer of one or more
electrons between reactants.
• Oxidation: loss of an electron (oxidized)
• Reduction: gain of an electron (reduced)
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Oxidation Reduction Reactions
• Redox Reactions: transfer of one or more
electrons between reactants.
• Oxidation: loss of an electron (oxidized)
• Reduction: gain of an electron (reduced)
• Na
+
Cl
Na+
+
Cl-
– Na = reducing agent b/c donates electron
– Cl = oxidizing agent b/c accepts electron
7 See Figure 9.3
Either transfer electrons or change degree of sharing.
Carbon in methane is oxidized as electrons move away; oxygen is
reduced as electrons move towards (for the chemistry lovers)
As electron moves towards lower energy level, energy is released.
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Oxidation of Glucose
• C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP)
– Glucose is oxidized to yield carbon dioxide
– Oxygen is reduced to yield water
• Organic molecules with abundance of hydrogen
are good source of high PE electrons that can
reduce oxygen.
• Must overcome activation energy
Glucose is source of electrons that fall closer to O2.
Electrons are associated with hydrogen so:
• O2 + e- + H+ H2O
– Spark/ignition—provides the energy
– Enzymes—lowers the energy required
From Glucose, electrons sent to electron acceptor. . .
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Figure 9.4 NAD+ as an electron shuttle
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Figure 9.5 An introduction to electron transport chains
First step: every 2 electrons and 2 protons removed from glucose
bound to NAD+
NAD+ is reduced and converted to NADH
o NAD+ + 2e- + H+NADH
o Nicotinamide adenine dinucleotide
o NAD+ is oxidizing agent.
Dehydrogenase: enzyme that removes electrons and protons and
attaches to NAD+
NADH stores energy and brings electrons to ETC
FADH2 will also serve as electron acceptors.
H2 + O2: explosive, electrons fall directly from H to O2
ETC breaks fall, gradual release of energy.
Oxygen is final electron acceptor
Path of electrons: Food NADH ETC O2
**Reason need food: supply of electrons that drives generation of ATP
**Reason need oxygen: catch/remove electrons at end of chain—if not,
electrons build up and process stops.
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Figure 9.6 An overview of cellular respiration (Layer 3)
Respiration—three stages
1. Glycolysis
a. Cytosol
b. glucose 2 pyruvate
2. Krebs Cycle
a. mitochondrial matrix
b. pyruvate CO2, NADH, FADH2 (flavin adenine
dinucleotide)
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3. ETC
a. Inner membrane of mitochondrion
b. 90% ATP generation
c. Electrons from NADH and FADH2
i. Combine with H and O2 H2O
NET: 1 glucose 38 ATP
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Figure 9.7 Substrate-level phosphorylation
Substrate Level
Phosphorylation
Enzyme transfers phosphate
from a donor molecule to
ADP
Oxidative Phosphorylation
ADP conversion to ATP
powered by redox reactions of
electron transport chain.
ATP Synthase
90% of ATP produced by
respiration.
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Figure 9.8 The energy input and output of glycolysis
Substrate Level Phosphorylation
• Enzyme transfers phosphate from substrate to ADP
Oxidative Phosphorylation
• ATP produced by redox reactions of ETC.
• Inner membrane of mitochondria
• ATP Synthase
• Chemiosmosis
Glycolysis: “splitting of sugar”
• Glucose 2 pyruvate
• Two phases: investment and payoff
• Ten steps, each catalyzed by specific enzyme
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Steps 1-5: ATP used to phosphorylate food molecules (make
more reactive)
Steps 6-10: ATP produced by SLP, NAD+ NADH
Net Yield: 2 ATP, 2 NADH, 2 pyruvate (pyruvate Krebs)
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*Does NOT require O2, no CO2 produced
Glycolysis takes place in cytosol.
Energy Investment
1. Hexokinase phosphorylates glucose
• Charge traps glucose in the cell
• Makes glucose more reactive
• ATP is energy source for endergonic steps of glycolysis
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Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2)
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DHAP G3P never reaches equilibrium.
G3P used up by next step, “pulls” DHAP to become G3P
Energy Payoff
Triose phosphate dehydrogenase acts on G3P
• “pulls” DHAP G3P 1,3,BPG
• Oxidizes sugar, H+and e- to NAD+
• Reaction very exergonic, uses energy to produce NADH and
attach phosphate to sugar (increasing reactivity)
Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)
Pyruvate still contains most of glucose’s energy
Glycolysis alone would be very inefficient
Krebs cycle harvests more energy.
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Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis
and the Krebs cycle
Pyruvate acetyl CoA
• Produce CO2
o Lose 1 carbon per pyruvate (2 per glucose molecule)
o Carbon produces CO2
o --note: CO2 completely from pyruvate; no oxygen used.
• NAD+ NADH + H+
• Combine with CoA to form acetyl CoA
• CoA from Vitamin B
Enzymes on inner membrane of mitochondria, transfer acetyl CoA inside
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Krebs Cycle (Citric Acid Cycle or TCA)
• 8 steps, each catalyzed by different enzyme
• 2 carbon in (Acetyl CoA)
• 2 carbon out (CO2)
• Each glucose produces 2 acetyl CoA
Occurs in mitochondrial matrix
Step 3: energy produced/stored as NADH as 1st CO2 released
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Step 4: energy produced/stored as NADH as 2nd CO2 released
*All 6 carbons from glucose are now CO2
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Step 5: produce ATP by SLP
Step 6: produce FADH2 (flavin adenine dinucleotide)
• Stores energy like NADH (but a little less)
• Produce ATP by oxphos in ETC
Krebs cycle produces 1 ATP by SLP
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Figure 9.11 A closer look at the Krebs cycle (Layer 4)
Step 8: produce NADH
Each turn produces
• 3NADH
• 2CO2
• 1 FADH2
• 1 ATP
1 glucose 2 turns
**from glucose, 2 C lost in pyruvate oxidation, 4 lost in Krebs
**one turn for each 2 carbon subunit that feeds into Krebs.
So far, 6 CO2 released—accounts for ALL carbons
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Figure 9.12 A summary of the Krebs cycle
09-12-KrebsCycle.swf
Figure 9.13 Free-energy change during electron transport
Animation
Figure 9.15
09-15-ElectronTransport.swf
Chemiosmosis couples the electron transport chain to ATP
synthesis
So far, 4 ATP generated
• 2 ATP by SLP from glycolysis
• 2 ATP by SLP from Krebs
Electron Transport Chain
• Molecules embedded in inner membrane
• Thousands per mitochondria
• Proteins with prosthetic groups that can be oxidized and reduced.
• Electrons from NADH and FADH2
• NADH and FADH2 oxidized and sent back to glycolysis/Krebs
• Electrons lose energy as move through system—where does it go?
o NO ATP MADE BY ETC
NADH 2.5ATP/NADH (ideally 3)
FADH2 1.5 ATP/FADH2
Movement of electron through electron carriers of ETC powers proton
pumps that pump H+ from matrix to IM space.
Establish proton gradient, “proton motive force”.
H+ will flow back down gradient spontaneously and release energy (as
ball rolling down hill).
Only region permeable to H+ is ATP synthase.
Move through and drive ATP synthase to convert ADP to ATP
oxidative phosphorylation
Chemiosmosis.
Back to previous slide. . .
• O2 is final electron acceptor, binds H and forms water.
• What happens if run out of O2?
• System backs up, stops pumping H+, no ATP generation
• THIS IS WHY WE NEED TO BREATHE!
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Figure 9.14 ATP synthase, a molecular mill
ATP Synthase
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Figure 9.16 Review: how each molecule of glucose yields many ATP molecules
during cellular respiration
Glycolysis 2 ATP
Pyruvate Oxidation 2 ATP
ETC 34 ATP
Usually < 38 because energy from H+ gradient harnessed and used for
other work (uptake of pyruvate from cytosol).
40-50% efficient; energy lost as heat body temperature
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Figure 9.17a Fermentation
Fermentation
• Occurs under anaerobic conditions
• Glycolysis generates NADH—if no oxygen, need alternate path
for harvesting energy and regenerating NAD+.
• ATP by SLP only
• Two types
o Alcohol fermentation
o Lactic acid fermentation
Alcohol Fermentation
• Produce Ethanol and CO2
• Alcoholic beverages
• Ethanol from corn and other organics for fuel.
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Figure 9.17b Fermentation
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Figure 9.18 Pyruvate as a key juncture in catabolism
Lactic Acid Fermentation
• Produce Lactate
• NO CO2 produced.
• Humans, fungi, bacteria (cheese yogurt).
• Produced during heavy exercise. Lactic acid accumulate in blood,
must later be converted back to glucose or pyruvic acid (requires
oxygen) = oxygen debt.
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Figure 9.19 The catabolism of various food molecules
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Figure 9.20 The control of cellular respiration
Review Questions
1. Explain how photosynthesis and respiration are related and connected.
2. What are some reasons that your cells need ATP?
3. State the reaction for cellular respiration
4. How is cellular respiration similar to and different from combustion?
5. During cellular respiration, which molecule is oxidized? Reduced?
6. In what subatomic particle can energy be stored?
7. Explain the general flow of events as illustrated in figures 9.6 and 9.16
8. Explain the function of NADH and FADH2.
9. Which contains more energy, NADH or NAD? Explain.
10. Where does glycolysis occur?
11. Memorize figure 9.8—for glycolysis, you need to know what goes in and what comes out.
12. A single molecule of glucose enters glycolysis. Into what molecules is glucose converted?
13. How many ATP are invested into glycolysis? How many ATP are produced by glycolysis? What is the
net gain of ATP through glycolysis?
14. Besides ATP and pyruvate, another molecule is produced during glycolysis. This molecule carries
energy from glycolysis to the ETC. What is this molecule?
15. Explain the role of phosphofructokinase in regulating glycolysis. Figure 9.20
16. Explain the process by which pyruvate is converted to acetyl CoA. What electron carrier is produced
during this reaction?
17. Where does the Kreb’s Cycle occur?
18. Explain the difference between Oxidative Phosphorylation and Substrate Level Phosphorylation? When
does each process occur?
19. For the Krebs cycle, you do not have to memorize each step. You do need to know—what goes in, what
comes out, where does the energy end up? Figure 19.16
20. What is the ultimate job of the electron transport chain?
21. Where do the high energy electrons that are fed into the electron transport chain come from?
22. Explain how ATP synthase functions.
23. What molecule is the final electron acceptor? When it binds electrons, what does it become?
24. On a molecular level, why does a lack of oxygen cause your cells to die?
25. Explain the processes of alcoholic fermentation and lactic acid fermentation