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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