Cell respiration is the

1. Cellular Respiration
Harvesting Chemical Energy

2. Decomposition pathways
 Release stored energy by breaking down
complex molecules
 Fermentation – partial breakdown of sugars
in absence of oxygen
 - anaerobic
 Cellular respiration – breakdown of organic
compounds requiring oxygen
 - aerobic

3. Cellular Respiration
 Overall process
Organic compounds + Oxygen
 Carbon dioxide + Water + Energy

4. Cellular Respiration
 Breakdown of glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O +
energy
 Energy released stored in ATP
 ATP provides energy to power most life
processes

5.  How do cells make ATP from the energy in
food?

6. Cellular Respiration
 Three stages
 Glycolysis
 Krebs cycle
 Electron transport chain (ETC)

7. Cellular Respiration
 Glycolysis does not need O2
 Krebs Cycle and electron transport chain do

8. Glycolysis
 Decomposition pathway
 Occurs in the cytoplasm
 1st stage of both anaerobic and aerobic
respiration

9. Glycolysis
 Glucose + ATP → Glucose-6-phosphate +
ADP
 G–6–P rearranges and combines with
another ATP → Fructose diphosphate

10. Glycolysis
 Fructose diphosphate → 2 3-carbon molecules
(PGAL)
 PGAL molecules rearranged to form pyruvic acid
(pyruvate)
 Releases energy, stored in 2 ATP molecules for each
reaction
 Electrons released from PGAL convert NAD+ →
NADH

12. Summary of Glycolysis
 For each molecule of glucose:
 2 molecules pyruvate
 2 NADH
 2 ATP (net): (4 ATP – 2ATP)

13. What happens next?
 Depends on whether or not O2 is present
 If O2 present, pyruvate enters mitochondria
for aerobic respiration
 If no O2 present, fermentation

14. Fermentation (Anaerobic respiration)
 NADH + pyruvate → NAD+ and lactate (also
a 3-carbon acid)
 NAD+ returns to glycolysis
 = Lactic Acid fermentation

15. Lactic acid fermentation
 Human muscle cells (when O2 scarce)
 Cheese and yogurt

16. Fermentation (Anaerobic respiration)
 Yeast:
 pyruvate + NADH → ethanol and CO2 + NAD+.
= Alcoholic Fermentation
 In both lactic acid and alcoholic fermentation,
no more ATP produced.

19. Aerobic vs. Anaerobic Respiration

20. Mitochondria
 Further steps of aerobic
respiration involve an
electron transport system
 In eukaryotic cells, the membrane for this is
in the mitochondria

22. Mitochondria
 “Powerhouse of the cell”
 Where most of the ATP is synthesized
 10-1000’s of mitochondria/cell

23. As the pyruvate is transported to the
mitochondria …..
 Pyruvate → Acetate
 Acetate + coenzyme A → Acetyl CoA
 Molecule of CO2 released
 NAD+ → NADH

24. Krebs cycle
 Decomposition pathway
 Occurs in mitochondrial matrix
 Acetyl CoA into CO2

25. Krebs Cycle
 Acetyl CoA + oxaloacetate (4-C)→ 6 carbon acid citrate (6-C)
 Coenzyme A released and recycled
 Citrate rearranged and oxidized (removal of electrons)
 Two of citrate’s carbons removed to form carbon dioxide
 Hydrogen atoms removed convert NAD+ → NADH

26. Krebs Cycle
 4-carbon molecule produced by citrate losing
2 carbons is rearranged and further oxidized
to become oxaloacetate
 Oxidation converts NAD+ to NADH and FAD
to FADH2→
 Energy released in these reactions used to
convert ADP + P → ATP

27. Krebs Cycle

28. Krebs cycle summary

29. For every turn of Krebs cycle
 Two C’s enter as acetyl CoA
 Two C’s are oxidized and leave as CO2
 Coenzymes NAD+ and FAD are reduced
 3 NADH and 1 FADH2 are produced
 One ATP produced
 Oxaloacetate is regenerated
 Note: Two turns are required for complete
oxidation of glucose

30.  Animation: How the Krebs Cycle Works (Quiz
1)

31. Cellular Respiration
 Three stages
 Glycolysis
 Krebs cycle
 Electron transport chain (ETC) and

32. Electron transport chain
 Uses inner membrane of mitochondrion
 Accepts energized electrons from reduced
coenzymes (NADH and FADH2)
 Uses the electrons for ATP synthesis
 produces most (90%) of ATP of aerobic
respiration

34. Electron transport chain (ETC)
 Electron carrier molecules called
cytochromes embedded in inner membrane
 H atoms of NADH and FADH2 are separated
into electrons and protons.
 Cytochromes transfer the electrons from one
to the next
 Last cytochrome is an enzyme that combines
electrons and protons with oxygen, forming
water

35. ETC
 With each transfer along the ETC, electrons
release free energy
 Used by proteins in the inner membrane to
actively transport protons from matrix to the
intermembrane space

36. Chemiosmosis
 Protons diffuse back across the membrane,
passing through an ATP-synthase complex
 ADP + P → ATP

37. ATP synthase
 Protons diffuse through ATP synthase
complex which converts ADP to ATP
 Cristae increase the surface area available
for chemiosmosis

39. ETC
 Electrons from each NADH can drive
synthesis of up to 3 ATP
 Electrons from each FADH2 can drive
synthesis of up to 2 ATP
 The 6 NADH and 2 FADH2 made from each
molecule of glucose can drive production of a
total of 22 ATP through the ETC

40. Overview of Cellular Respiration

41. Cellular Respiration
36 – 38 ATPs per glucose
Process Reduced
Coenzyme
ETC
Total
ATP
glycolysis
Net
2 ATP 2 NADH 4 - 6 ATP 6 - 8
Oxidation
of pyruvate
--
2 NADH 6 ATP 6
Krebs
cycle 2 ATP
6 NADH
2 FADH2
18 ATP
4 ATP 24

42. ETC
 For every two NADH, one O2 is reduced to
two H2O molecules

43. Cellular Respiration
 Estimated efficiency = 38%
 Energy lost in the process is lost as heat.

44. Related Metabolic Processes

45. Bacteria
 No mitochondria
 ETC occur in cell membrane
 Some bacteria use oxidizers other than
oxygen
 E.g. SO4
-2 , NO3
-

46. Facultative anaerobes
 Organisms capable of growth in either
aerobic or anaerobic environments
 Yeast, many bacteria, mammalian muscle cells

47. Obligate anaerobes
 Bacteria that are poisoned by O2.
 Can only do fermentation or anaerobic
respiration.

48. Obligate aerobes
 Us! (And all other animals and plants)
 Cannot survive without O2

49. Evolutionary significance of glycolysis
 First prokaryotes produced ATP by glycolysis
 Why do we think this?

50.  Complex molecules can be hydrolyzed to
intermediates of glycolysis or Krebs cycle

51.  Starch, glycogen, disaccharides  glucose

52.  Proteins  amino acids  deaminated  . . .

53.  Fats 
 Glycerol  glyceraldehyde phosphate (PGAL)
 Fatty acids  acetyl CoA

56. Yeast that are facultative anaerobes use
more glucose when there is less oxygen
 Why?
 ATP acts as an inhibitor of
phosphofructokinase
 With fermentation, less ATP is produced
 Less inhibition of glycolysis

57. Control of Respiration
 What happens to glucose taken in as food?
 Depends on energy needs
 If low energy demand, stored as starch
(plants) or glycogen (animals). Fats also
stored.
 If high energy demand, broken down in cell
respiration