1. How Cells Harvest Chemical Energy
Chapter 6
How Cells Harvest Chemical Energy

2. How Is a Marathoner Different from a Sprinter?
How Is a Marathoner Different from a Sprinter?
Muscles in human legs contain two different types of muscle fibers
Marathoners have more slow-twitch fibers, which perform better in endurance exercises
Sprinters have more fast-twitch fibers, which perform best in short bursts of intense activity

4. The different types of muscle fibers use different processes for making ATP
Slow-twitch fibers undergo aerobic (in the presence of O2) respiration
Fast-twitch fibers undergo anaerobic (in the absence of O2) respiration
Cellular respiration is the process by which cells produce energy aerobically

5. INTRODUCTION TO CELLULAR RESPIRATION
6.1 Photosynthesis and cellular respiration provide energy for life
All living organisms require energy to maintain homeostasis, to move, and to reproduce
Photosynthesis converts energy from the sun to glucose and O2
Cellular respiration breaks down glucose and releases energy in ATP
Energy flows through an ecosystem; chemicals are recycled

6. LE 6-1 Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO2
Glucose
H2O O2
Cellular respiration
in mitochondria
ATP
(for cellular work)
Heat energy

7. 6.2 Breathing supplies oxygen to our cells and removes carbon dioxide
6.2 Breathing supplies oxygen to our cells and removes carbon dioxide
Breathing and cellular respiration are closely related
Breathing brings O2 into the body from the environment
O2 is distributed to cells in the bloodstream
In cellular respiration, mitochondria use O2 to harvest energy and generate ATP
Breathing disposes of the CO2 produced as a waste product of cellular respiration

8. LE 6-2 O2 Breathing CO2 Lungs CO2 Bloodstream O2
Muscle cells carrying out
Cellular Respiration
Glucose  O2
CO2  H2O  ATP

9. 6.3 Cellular respiration banks energy in ATP molecules
6.3 Cellular respiration banks energy in ATP molecules
The reactants O2 and glucose regroup to form the products CO2 and H2O
Energy from glucose is released and stored in ATP

10. LE 6-3
Glucose
Oxygen gas
Carbon
dioxide
Water
Energy

11. CONNECTION
6.4 The human body uses energy from ATP for all its activities
The body needs a continual supply of energy to maintain basic functioning
In addition, ATP supplies energy (kilocalories) for voluntary activities
An average adult human needs about 2,200 kcal of energy each day

13. 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
The energy available to a cell is contained in the arrangement of electrons in chemical bonds
Electrons lose potential energy when they “fall” from organic compounds to oxygen during cellular respiration
Each step of the “fall” involves paired oxidation–reduction (redox) reactions
Oxidation: loss of electrons (in atoms)
Reduction: addition of electrons

14. The redox reactions of cellular respiration
Glucose loses electrons (in H atoms) and becomes oxidized
O2 gains electrons (in H atoms) and becomes reduced
Along the way, the electrons lose potential energy, and energy is released

16. The redox reactions that break down glucose involve an enzyme and a coenzyme
The enzyme dehydrogenase removes electrons (in H atoms) from fuel molecules (oxidation)
The electrons are transferred to the coenzyme NAD+, which is converted to NADH (reduction)

17. Oxidation
Dehydrogenase
Reduction
NAD 2H
NADH H
(carries
2 electrons)
2H  
2 e

18. NADH passes electrons to an electron transport chain
As electrons “fall” from carrier to carrier and finally to O2, energy is released in small quantities
The energy released is used by the cell to make ATP

19. Controlled release of energy for synthesis Electron transport chain
NADH
ATP
NAD
2e
Controlled
release of
energy for
synthesis
of ATP H
Electron transport
chain
2e 2 1 O2 H 2
H2O

20. STAGES OF CELLULAR RESPIRATION AND FERMENTATION
6.6 Overview: Cellular respiration occurs in three main stages
Stage 1: Glycolysis
Occurs in the cytoplasm
Breaks down glucose into pyruvate, producing a small amount of ATP
Produces NADH

21. Stage 2: The citric acid cycle
Stage 2: The citric acid cycle
Takes place in the mitochondria
Completes the breakdown of glucose, producing CO2 and a small amount of ATP
Supplies the third stage of cellular respiration with electrons
Produces NADH and FADH2

22. Stage 3: Oxidative phosphorylation
Stage 3: Oxidative phosphorylation
Occurs in the mitochondria
Uses the energy released by electrons “falling” down the electron transport chain to pump H+ across a membrane
Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

23. High-energy electrons
NADH
High-energy electrons
carried by NADH
NADH
FADH2
and
GLYCOLYSIS
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
Glucose
Pyruvate
Cytoplasm
Mitochondrion
CO2
CO2
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation

24. 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
Glycolysis splits sugar molecules in the cytoplasm
Starts with a single 6-carbon molecule of glucose
Ends with two 3-carbon molecules of pyruvate
Produces two molecules of ATP in the process

25. LE 6-7a 2
NAD 2
NADH 2 H
Glucose
2 Pyruvate
2 ADP 2 P 2
ATP

26. Glycolysis produces ATP by substrate-level phosphorylation
Glycolysis produces ATP by substrate-level phosphorylation
An enzyme transfers a phosphate group from an organic molecule to ADP
A small amount of ATP is produced

27. Organic molecule (substrate)
LE 6-7b
Enzyme P P P
Adenosine
ADP
ATP P
Organic molecule
(substrate) P

28. Details of glycolysis
Preparatory phase
A fuel molecule (glucose) is energized, using ATP
A 6-carbon intermediate splits into two 3-carbon intermediates
Energy payoff phase
A redox reaction generates NADH
ATP and pyruvate are produced

32. X 2!

33. http://www. science. smith. edu/departments/Biology/Bio231/glycolysis

34. 6.8 Pyruvate is chemically groomed for the citric acid cycle
A large, multienzyme complex catalyzes three reactions in the mitochondrial matrix
A carbon atom is removed from pyruvate and released in CO2
The remaining two-carbon compound is oxidized, and a molecule of NAD+ is reduced to NADH
Coenzyme A joins with the 2-carbon group to produce acetyl CoA

35. + LE 6-8 NAD+ NADH H+ CO2 CoA Pyruvate Acetyl CoA (acetyl coenzyme A)

36. 6.9 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules
For each turn of the citric acid cycle
Two CO2 molecules are released
The energy yield is one ATP, three NADH, and one FADH2

37. + + LE 6-9a Acetyl CoA CITRIC ACID CYCLE CoA CoA 2 CO2 3 FADH2 NAD+
NADH +
3 H+
ATP +
ADP P

38. Details of the citric acid cycle
The 2-carbon acetyl part of acetyl CoA is oxidized
The two carbons are added to a 4-compound, forming citrate
Through a series of redox reactions, two carbons are removed from citrate as CO2 and the 4-carbon compound is regenerated
The energy-rich molecules ATP, NADH, and FADH2 are produced

39. LE 6-9b +H+ + H+ + +H+ CoA Acetyl CoA CoA 2 carbons enter cycle
Oxaloacetate
Citrate
NADH
+H+
leaves
cycle
CO2
NAD+
NAD+
CITRIC ACID CYCLE
Malate
NADH
+ H+
ADP + P
FADH2
ATP
Alpha-ketoglutarate
FAD
leaves
cycle
CO2
Succinate
NADH
+H+
NAD+

41. 6.10 Most ATP production occurs by oxidative phosphorylation
6.10 Most ATP production occurs by oxidative phosphorylation
An electron transport chain in the mitochondrial membrane creates a H+ gradient
Electrons from NADH and FADH2 travel down the chain to O2, which picks up H+
H2O is formed as a product
Energy released by redox reactions actively transports H+ across the membrane from the mitochondrial matrix to the intermembrane space

42. In chemiosmosis, ATP synthases drive the synthesis of ATP
Exergonic reactions of the electron transport chain produce an H+ gradient that stores potential energy
ATP synthases harness the energy by acting like turbines
Help the H+ diffuse back down the gradient through the inner membrane
Attach phosphate groups to ADP, producing ATP

43. LE 6-10 H+ H+ H+ H+ H+ H+ H+ + + H+ Protein complex Electron carrier
ATP
synthase
Intermembrane
space
Inner
mitochondrial
membrane
FADH2
FAD
Electron
flow 1 2
NADH
NAD+ O2 + 2 H+ H+
Mitochondrial
matrix H+
ADP + P
ATP H+
H2O H+
Electron Transport Chain
Chemiosmosis
OXIDATIVE PHOSPHORYLATION

44. CONNECTION
6.11 Certain poisons interrupt critical events in cellular respiration
Rotenone, cyanide, and carbon monoxide block parts of the electron transport chain
Oligomycin blocks the passage of H+ through ATP synthase
Uncouplers such as DNP destroy the H+ gradient by making the membrane leaky to H+

45. Cyanide, carbon monoxide Electron Transport Chain
Rotenone
Cyanide, carbon monoxide
Oligomycin H+ H+ H+
ATP synthase H+ H+ H+ H+ H+ H+
DNP
FADH2
FAD
1 2 O2 + 2 H+
NADH
NAD + H+
ADP + P
ATP H+
H2O H+
Electron Transport Chain
Chemiosmosis

46. 6.12 Review: Each molecule of glucose yields many molecules of ATP
Glycolysis and the citric acid cycle together yield four ATP per glucose molecule
Oxidative phosphorylation, using electron transport and chemiosmosis, yields 34 ATP per glucose
These numbers are maximums
Some cells may lose a few ATP to NAD+ or FAD shuttles

47. LE 6-12 Cytoplasm + 2 ATP + 2 ATP + about 34 ATP
Electron shuttle across membrane
Cytoplasm
Mitochondrion 2
NADH 2
NADH
(or 2 FADH2) 2
NADH 6
NADH 2
FADH2
GLYCOLYSIS
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
2 Pyruvate
2 Acetyl CoA
CITRIC ACID CYCLE
Glucose
+ 2 ATP
+ 2 ATP
+ about 34 ATP
by substrate-level phosphorylation
by substrate-level phosphorylation
by oxidative phosphorylation
About 38 ATP
Maximum per glucose:

48. 6.13 Fermentation is an anaerobic alternative to cellular respiration
6.13 Fermentation is an anaerobic alternative to cellular respiration
Fermentation
Generates two ATP molecules from glycolysis in the absence of oxygen
Recycles NADH to NAD+ anaerobically
Muscle cells use lactic acid fermentation
NADH is oxidized to NAD+ as pyruvate is reduced to lactate

49. + LE 6-13a 2 Lactate NAD NADH NADH NAD P ATP 2 ADP 2 2 2 2
GLYCOLYSIS
2 ADP + 2 P 2
ATP
2 Pyruvate
2 Lactate
Glucose

50. Alcohol fermentation occurs in brewing, wine making, and baking
NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol

51. + LE 6-13b NAD NADH NADH NAD 2 ADP P ATP CO2 released 2 Ethanol 2 2
GLYCOLYSIS
2 ADP + 2 P 2
ATP 2
CO2
released
Glucose
2 Pyruvate
2 Ethanol 2

53. Facultative anaerobes
Strict anaerobes
Require anaerobic conditions to generate ATP by fermentation
Are poisoned by oxygen
Facultative anaerobes
Can make ATP by fermentation or oxidative phosphorylation depending on whether O2 is available

54. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS
6.14 Cells use many kinds of organic molecules as fuel for cellular respiration
Cells use three main kinds of food molecules to make ATP
Carbohydrates
Hydrolyzed by enzymes to glucose, which enters glycolysis

55. Proteins
Digested to constituent amino acids, which are transformed into various compounds
Become intermediates in glycolysis or the citric acid cycle

56. Fats Digested to glycerol and free fatty acids
Glycerol becomes an intermediate in glycolysis
Fatty acids are broken into 2-carbon fragments that enter the citric acid cycle as acetyl CoA

57. OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Food, such as peanuts
Carbohydrates
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
CITRIC ACID CYCLE
Glucose
G3P
Acetyl CoA
Pyruvate
GLYCOLYSIS
ATP

58. 6.15 Food molecules provide raw materials for biosynthesis
6.15 Food molecules provide raw materials for biosynthesis
Some raw materials from food can be incorporated directly into an organism’s molecules
Cells can also make molecules not found in food
Intermediate compounds of glycolysis and the citric acid cycle act as raw materials
Biosynthetic pathways consume ATP rather than generate it
Biosynthesis is not always the direct reverse of breakdown pathways

59. ATP needed to drive biosynthesis Cells, tissues, organisms
LE 6-15
ATP needed to drive biosynthesis
ATP
GLUCOSE SYNTHESIS
CITRIC ACID CYCLE
Acetyl CoA
Pyruvate
G3P
Glucose
Amino groups
Amino acids
Fatty acids
Glycerol
Sugars
Proteins
Fats
Carbohydrates
Cells, tissues, organisms

60. 6.16 The fuel for respiration ultimately comes from photosynthesis
6.16 The fuel for respiration ultimately comes from photosynthesis
All organisms can harvest energy from organic molecules
Plants can also make molecules from inorganic sources by photosynthesis
Cellular respiration Review video: