1. Why do we need sugar? What is cellular respiration? sugar contains energy, cells need to access...
Transcript of 1. Why do we need sugar? What is cellular respiration? sugar contains energy, cells need to access...
1. Why do we need sugar? What is cellular respiration?
• sugar contains energy, cells need to access it• sugar is broken down to make ATP
• 6O2 + C6H12O6 6CO2 + 6H2O + energy (ATP)
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1. Goal of cellular respiration• make ATP (energy form cells can use)
• ATP is made when mitochondria break down sugars
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2. Glycolysis• 1 glucose (6C molecule)
2 pyruvates (3C molecules)
• happens in cytosol of all cells (facilitated diffusion of glucose into cytosol)
• need 2 ATP to start
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Glycolysis – Step 1• 2 ATP to start (2 ATP 2 ADP + 2 P)
• new 6C compound is formed when 2P are attached to glucose
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Glycolysis – Step 2
• new 6C compound splits into 2 G3P (3C each)
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Glycolysis – Step 3
• 2 G3P gain 2P and lose 4e- (2 G3P + 2P – 4e- 2 new 3C compounds)
• 4 e- “picked up” by NAD+ (2 NAD+ + 4e- + 2H+ 2 NADH “batteries”)
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Glycolysis – Step 4• 4P removed from 3C compounds
2 pyruvate molecules (3C each)
• 4 ADP + 4 P 4 ATP “batteries”
• NET YIELD of 2 ATP (2 ATP are needed to start glycolysis)
• MOST of the energy is still “trapped” in the 2 pyruvates
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3. What happens next? Two pathways…
• ANAEROBIC respiration (cytosol)
• NO O2
• some unicellular organisms can “get by” with this
• leads to fermentation
• alcohol or lactic acid made
• AEROBIC respiration (mitochondria)
• O2 present
• all energy in pyruvate is released
• larger organisms need this8
4. Anaerobic pathway – alcoholic fermentation
• pyruvate (3C) ethanol (2C) and CO2
• CO2 removed, 2 hydrogen added ethyl alcohol (2C) formed
• NAD+ electron carrier regenerated (used in glycolysis)
• 2 ATP (from glycolysis)
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4. Alcoholic fermentation – yeast
• yeast (unicellular eukaryote - fungus)
• enzymes in cytosol are needed for alcoholic fermentation
• ethyl alcohol accumulates to a point
• wine – CO2 released (wine) or stays in (champagne)
• bread – CO2 makes bread “fluffy”, alcohol evaporates when baked
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5. Anaerobic pathway – lactic acid fermentation
• pyruvate (3C) converted to lactic acid (3C)
• NAD+ electron acceptor regenerated (used in glycolysis)
• 2 ATP (from glycolysis)
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5. Lactic acid fermentation – bacteria, fungi, muscles
• bacteria and fungi
• bacteria or fungi is added to milk
• sugar in milk converted is to lactic acid cheese or yogurt is made
• muscles
• during strenuous exercise, O2 is used up
• lactic acid accumulates muscle aches and pains (acidic cytosol)
• lactic acid diffuses into the blood liver converted back to pyruvic acid when O2 becomes available
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6. Aerobic pathway• Two parts
• Krebs cycle – make “batteries”, 2ATP
• electron transport chain (ETC) and chemiosmosis – use “batteries” to make LOTS of ATP
• OXYGEN needed! • It’s the “clean up guy”.
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7. Mitochondria• Prokaryotes
• no mitochondria
• all respiration in cytosol
• Eukaryotes
• mitochondria
• pyruvate diffuses into mitochondrial matrix
• pyruvate (3C) + coenzyme A “bus” acetyl CoA (2C) + CO2
(released)
• NADH “battery” formed (NAD+ + 2e- + H+ NADH)
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8. The Krebs Cycle - Overview• Krebs Cycle goal = make
BATTERIES
• happens in mitochondrial matrix
• ATP (useable form of energy) made
• NADH, FADH2 “batteries” used to make LOTS of ATP using the Electron Transport Chain (ETC)
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Krebs Cycle Diagram
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Step 1• acetyl CoA (2C) “delivered to”
Krebs Cycle
• 2C + 4C = 6C citric acid made
• coenzyme A “bus” regenerated
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Step 2• NADH “battery” made
• CO2 released
• 5C compound made
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Step 3• NADH “battery” made
• CO2 released again
• 4C compound
• ATP made (ADP + P ATP)
• new 4C compound made
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Step 4• FADH2 “battery” is made
(FAD + 2H+ + 2e-)
• new 4C compound made
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Step 5• 4C compound releases H
and regenerates 4C compound needed for Step 1
• NADH “battery” made
• keeps Krebs cycle going
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Krebs Cycle Totals• 1 glucose causes TWO
TURNS of the Krebs cycle (1 pyruvate processed at a time)
• 10 NADH “batteries” made
• glycolysis = 2
• entering Krebs = 2
• Krebs cycle = 6
• 2 FADH2 “batteries” made
• 2 ATP made
• 6 CO2 given off as waste
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9. Electron Transport Chain - Overview
• Let’s make ATP!
• happens in cristae (lots of folds lots of ATP) of mitochondria
• uses NADH and FADH2 “batteries”
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Electron Transport Chain Diagram
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9. Electron Transport Chain – Details
• NADH and FADH2 release H+ and e-
• e- move down ETC (lose energy)
• energy used for H+ pump• H+ PUMPED OUT of
mitochondrial matrix to inner membrane space
• H+ ions then DIFFUSE INTO mitochondrial matrix through ATP synthase
• ATP synthase spins = CHEMIOSMOSIS
• ADP + P ATP 25
10. Why is oxygen needed?• oxygen picks up leftover e-
from ETC and leftover H+ ions
• allows ATP to continue to be made
• prevents a “traffic jam of e- and H+
• H2O released (O2 + 4e- + 4H+ 2H2O)
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11. Energy Yield• glycolysis: _____ ATP total
• Krebs cycle: _____ ATP total
• each NADH: _____ ATP (x 10)
• each FADH2: _____ ATP (x 2)
• 2 ATP
MAXIMUM of _____ ATP (depends on cell and conditions)
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12. How efficient is cellular respiration?
• Your car? 20-25% efficient
• Your cells? 66% efficient
• remaining energy lost as HEAT
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