1. A way to transform energy to a useable form for organisms.
Cellular Respiration
Chapter 7 AP Biology
A way to transform energy to a useable form for organisms.
ATP

2. powers most cellular work
Life is Work!
Sun: ultimate source of energy
Photosynthesis: takes light E and converts it to food, autotrophs
Cellular Respiration: uses the food energy and converts it to ATP, autotrophs and heterotrophs
Generates ATP & Releases heat
Excess free energy results in growth & storage
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
Organic molecules
+ O2
ATP
powers most cellular work
Heat energy

3. Redox Reactions Reduction Oxidation
Gain of electrons
Oxidizing Agent (electron acceptor)
Oxygen: the final electron acceptor!
Oxygen is strongly electronegative, as the e- leaves glucose, & goes to oxygen, free E is released
Oxidation
Loss of electrons
Reducing Agent (electron donor)
Glucose
Oxidized in steps using a coenzyme (NAD+) and hydrogen atoms to strip the electrons from glucose & release E
becomes oxidized
becomes reduced

4. NAD+ Energy harvest and the Electron Transport Chain (ETC)
NAD+ - nicotinamide adenine dinucleotide is a coenzyme that transports electrons from glucose to the electron transport chain to make ATP
NAD+ is reduced to NADH + H+ (remove a pair of H atoms from food molecule, oxidized)
NADH Carries electrons to the ETC (electron transport chain) to release free energy
Glucose is broken down in a series of steps to slowly harvest the free energy from “falling” electrons more efficiently
The e- travel with a H+
The H+ ‘s ride along on NAD+

5. Stages of Cellular Respiration C6H12O6 + O2  6CO2 + 6H2O + ATP 09_06CellularRespiration.mpg
Glycolysis
Oxidize Glucose
Make Pyruvate
Citric Acid Cycle (aka Krebs Cycle)
Oxidize Pyruvate to Acetyl CoA
Regenerate C molecules, give off CO2
Oxidative Phosphorylation (aka Electron Transport)
Chemiosmosis
ATP Synthesis
Cytosol
2 ATP
Mitochondrial matrix
2 ATP
Inner Mitochondrial Membrane
32 ATP

6. Electrons carried via NADH Electrons carried via NADH and FADH2
Fig
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Mitochondrion
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation

7. Glycolysis: breaking glucose into two 3 C pyruvate molecules
Substrate Level Phosphorylation
small amounts of ATP, made by transferring P group from substrate to ADP
Occurs in the cytosol
Used in fermentation and respiration, ancient process
Converts glucose (6C)  2 pyruvate (3C) (pyruvic acid)
Uses 2 ATP – energy investment
Produces 4 ATP + 2 NADH – energy payoff
NET production = 2 ATP + 2 NADH

8. Between Glycolysis and Citric Acid Cycle
Most of glucose energy is stored in Pyruvate
Pyruvate’s carboxyl group (already oxidized) broken off and released as CO2 WASTE!
Follow the Carbon: Now the 2 C fragment is oxidized (e- removed) and the e- are transferred to NAD+
Enzyme conversion of remaining C to acetyl CoA

9. Citric Acid Cycle – Krebs Cycle complete energy-yielding oxidation of organic molecules
Substrate Level Phosphorylation
Small amounts of ATP
Occurs in the Mitochondrial Matrix
Converts 2 Acetyl CoA  6 NADH, 2 FADH2, 2 ATP and 4CO2
The CAC must turn twice for each molecule of glucose
See pg

10. Electron Transport Chain
Oxidative Phosphorylation
lots of ATP
Electrons from food carried in NADH & FADH2 move down ETC & release energy
Electroneg. Oxygen pulls e-
Occurs in the inner mitochondrial membrane
Electrons stored in NADH and FADH2 from glycolysis and the CAC are transported to the ETC where ~ 32 ATP are created
NADH + FADH2 + O2  ATP + H2O

11. Chemiosmosis & Electron Transport
Proteins carry electrons through the ETC while H+ pumps (oxidizing NADH to NAD+) pump H+ out into the cristae
The H+’s create an electrochemical gradient
As H+’s pass through the enzyme ATP synthase, ATP is made powered by flow of H+ across the membrane

12. Process Where? Phosphorylation Input Output
1. Glycolysis
2. Pyruvate  Acetyl CoA
3. Citric Acid Cycle (Kreb’s)
4. Electron Transport Chain (ETC)
TOTAL

13. Mitochondria

14. Process Where? Phosphorylation Input Output
1. Glycolysis
Cytosol
Substrate Level
2 ATP + Glucose
4 ATP + 2 NADH + 2 pyruvate
2. Pyruvate  Acetyl CoA
Mitochondrial Matrix
N/A
2 pyruvate
2 CO2 + 2 NADH + 2 Acetyl CoA
3. Citric Acid Cycle (Kreb’s)
2 Acetyl CoA
6 NADH + 2 FADH2 + 2 ATP + 4CO2
4. Electron Transport Chain (ETC)
Inner Mitochondrial Membrane
Oxidative
10 NADH + 2 FADH2 + O2
~ 32 ATP + H2O
TOTAL
Cytosol + Mitochondria
Glucose + O2
H2O + CO ATP

15. Anaerobic Respiration (ETC) Fermentation (no ETC) CYTOSOL
Uses Glycolysis and the ETC, but O2 is not the final e- acceptor
One ex: sulfate reducing bacteria use the SO42- ion at the end of the ETC, a by-product is H2S (icky smell, thermal vent bacteria)
Not as efficient as aerobic respiration
Fermentation
Oxidizes food w/out O2 & w/out Cellular Respiration.
Still uses glycolysis & NAD+ to generate ATP from food source
Alcoholic or Lactic Acid Fermentation are most common

16. Fermentation: Glycolysis then:
Lactic Acid
1. Pyruvate is reduced directly by NADH to form lactate (lactate is the form lactic acid takes when it gains e-)
2. Human muscle cells do this when O2 is scarce
Summary
Glycolysis – glucose  2 pyruvate
2 pyruvate  2 Lactate
09_18FermentationOverview_A.swf
Alcoholic
CO2 released from pyruvate then converted to acetaldehyde
Acetaldehyde reduced by NADH to ethanol
Summary
Glycolysis – glucose  2 pyruvates
2 Pyruvate  Ethanol + CO2

17. What is the evolutionary significance of Glycoysis?
Glycolysis: a metabolic pathyway that breaks down glucose to produce pyruvate and ATP w/out O2 and w/out a membrane bound organelle, it just takes place in the cytosol of a cell.
Likely the first way to generate cellular energy from food sources.
Would have worked when earth did not have an O2 rich atmosphere and when eukaryotic cells didn’t exist! How cool is that?

18. Respiration vs. Fermentation
Aerobic Respiration O2
Mitochondria
Electron Acceptor is O2
~36-38 ATP (depends on amt of O2 available to the cell.)
Free Energy becomes available for metabolism by the converstion of ATP to ADP & inorganic phosphate
Anaerobic Respiration
No O2
Cytosol
ETC w/ alternative final electron acceptors
ATP production variable
Fermentation (a type of anaerobic metabolism)
Electron Acceptors are Ethanol or Lactate
2 ATP

19. Heterotrophs don’t eat just glucose
Amino
acids
Sugars
Glycerol
Fatty
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citric
acid
cycle
Oxidative
phosphorylation
Fats
Proteins
Carbohydrates
Figure 9.19
Proteins, Lipids and Carbs may enter the process of respiration at various locations
Glucose provides the most direct ATP

20. Feedback Mechanisms & Respiration Regulation
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
ATP
Acetyl CoA
Citric
acid
cycle
Citrate
Oxidative
phosphorylation
Stimulates
AMP + –
Figure 9.20
Allosteric regulation of enzymes control cellular respiration by either preventing an enzyme from catalyzing a reaction OR by allowing an enzyme to catalyze a reaction.

21. Concept Check
What would happen if a disulfide bridge in cytochrome C did not form correctly in a cell?