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?
Human muscles contain two different types of muscle fibers that perform differently under different conditions
The ratio of types of fibers is determined genetically and cannot be converted from one type to another.

3. The different types of muscle fibers function either aerobically, with oxygen, or anaerobically, without oxygen.
The slow muscle fibers are muscle cells that can sustain repeated, long contractions but don’t generate a lot of quick power for the body.
Fast fibers are better able to produce ATP anaerobically
Cellular respiration
Is the process by which cells produce energy aerobically

4. INTRODUCTION TO CELLULAR RESPIRATION
6.1 Photosynthesis and cellular respiration provide energy for life
In photosynthesis, which occurs in the chloroplast, the energy of sunlight is used to rearrange the atoms of CO2 and H2O to produce glucose and O2.
In cellular respiration, which occurs in the mitochondria, O2 is consumed as glucose is broken down to CO2 and H2O.
The CO2 and H2O released by cellular respiration are converted through photosynthesis to glucose and O2, which are then used in respiration.

5. The processes of photosynthesis and cellular respiration are complementary. During these energy conversions, some energy is lost in the form of heat.
Photosynthesis uses solar energy to produce glucose and O2 from CO2 and H2O
Sunlight energy
ECOSYSTEM
Photosynthesis in chloroplasts
CO2
Glucose  
H2O O2
Cellular respiration in mitochondria
ATP
(for cellular work)
Heat energy
Figure 6.1

6. 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 provides for the exchange of O2 and CO2 between an organism and its environment
Respiration is gas exchange, and cellular respiration produces ATP. O2
CO2
Breathing
Lungs
CO2
Bloodstream O2
Muscle cells carrying out
Cellular Respiration
Glucose  O2
Figure 6.2
CO2 H2O ATP

7. 6.3 Cellular respiration banks energy in ATP molecules
6.3 Cellular respiration banks energy in ATP molecules
Cellular respiration breaks down glucose molecules and banks their energy in ATP
C6H12O6 + 6 O2 6
CO2 + 6
H2O +
ATPs
Glucose
Oxygen gas
Carbon dioxide
Water
Energy
Figure 6.3

8. Cellular respiration:
Consumes glucose.
Produces water.
Produces carbon dioxide.
Releases heat.
Is accomplished by many steps.

9. 6.4 The human body uses energy from ATP for all its activities
CONNECTION
6.4 The human body uses energy from ATP for all its activities
ATP powers almost all cellular and body activities
Table 6.4

10. Humans use the calories they obtain from food as their source of energy.
Humans use about 75% of their daily calories for involuntary life-sustaining activities such as digestion, circulation, and breathing.

11. 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
During cellular respiration, the energy in glucose is carried by electrons.
Electrons lose potential energy during their transfer from organic compounds to oxygen
Oxidation is the loss of electrons, and reduction is the gain of electrons.

12. When glucose is converted to carbon dioxide it loses hydrogen atoms, which are added to oxygen, producing water
Loss of hydrogen atoms (oxidation)
C6H12O6 +
6 O2
6 CO2 +
6 H2O +
Energy
Glucose
(ATP)
Gain of hydrogen atoms (reduction)
Figure 6.5A

13. In biological systems, dehydrogenase is an important enzyme involved in the regulation of redox reactions.
Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation) and transfers them to NAD+ (reduction)
Oxidation H O H O + 2H
Dehydrogenase
Reduction
NAD+_ + 2H
NADH + H
(carries
2 electrons)
2H+ +
2e
Figure 6.5B

14. Electron transport chain
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
NADH
NAD
ATP 
2e H
Controlled release of energy for synthesis of ATP
Electron transport chain
2e 2 H 1 O2 2
H2O
Figure 6.5C

15. STAGES OF CELLULAR RESPIRATION AND FERMENTATION
6.6 Overview: Cellular respiration occurs in three main stages
Cellular respiration
Occurs in three main stages

16. Do Now
What are the three stages of cellular respiration?

17. Stage 1: Glycolysis
Occurs in the cytoplasm
Breaks down glucose into pyruvate, producing a small amount of ATP

18. Stage 2: The citric acid cycle
Takes place in the mitochondrial matrix
Completes the breakdown of glucose, producing a small amount of ATP
Supplies the third stage of cellular respiration with electrons

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

20. http://www.youtube.com/watch?v=AdtAu5JgOV0&feature=related Figure 6.6
NADH
High-energy electrons carried by NADH
NADH
FADH2
and
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
GLYCOLYSIS
Glucose
CITRIC ACID CYCLE
Pyruvate
Mitochondrion
Cytoplasm
CO2
ATP
CO2
ATP
ATP
Substrate-level phosphorylation
Substrate-level phosphorylation
Oxidative phosphorylation
Figure 6.6

21. 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
“Splitting of sugar”
Glycolysis is the universal energy-harvesting process of life.

22. In glycolysis, ATP is used to prime a glucose molecule which is split into two molecules of pyruvate H 2
NAD+ 2
NADH + 2
Glucose
2 Pyruvate +
2 ADP 2 P 2
ATP
Figure 6.7A

23. Organic molecule (substrate)
Glycolysis produces ATP by substrate-level phosphorylation in which a phosphate group is transferred from an organic molecule to ADP
Enzyme P P P
Adenosine
ADP
ATP P
Organic molecule (substrate) P
Figure 6.7B

24. PREPARATORY PHASE (energy investment)
In the first phase of glycolysis, ATP is used to energize a glucose molecule, which is then split in two small sugars that are now primed to release energy.
 Steps      –   A fuel molecule is energized, using ATP. 1 3
Glucose
PREPARATORY PHASE (energy investment)
ATP
Step 1
ADP P
Glucose-6-phosphate 2 P
Fructose-6-phosphate
ATP 3
ADP P P
Fructose-1,6-diphosphate
 Step      A six-carbon intermediate splits into two three-carbon intermediates. 4 4
Figure 6.7C

25. In the second phase of glycolysis ATP, NADH, and pyruvate are formed
Glyceraldehyde-3-phosphate (G3P)
 Step     A redox reaction generates NADH. 5 6 9
NAD  5
NAD  5
ENERGY PAYOFF PHASE
NADH P 6 6
NADH P
+H
+H P P P P
1,3 -Diphosphoglycerate
 Steps     –      ATP and pyruvate are produced. 6 9
ADP
ADP 6 7 6 7
ATP
ATP P P
3 -Phosphoglycerate 7 7 P P 8 8
2-Phosphoglycerate 8 8
H2O
H2O P P
Phosphoenolpyruvate (PEP)
ADP 9
ADP 9 9 9
ATP
ATP
Pyruvate
Figure 6.7C

26. Glycolysis Overview
The result of glycolysis is a conversion of glucose to two three-carbon compounds, that we call pyruvate.
The end products of glycolysis are ATP, NADH, and pyruvate.

27. Acetyl CoA (acetyl coenzyme A)
6.8 Pyruvate is chemically groomed for the citric acid cycle
Prior to the citric acid cycle, enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA
NAD
NADH
 H 2
CoA
Pyruvate
Acetyl CoA (acetyl coenzyme A) 1 3
CO2
Coenzyme A
Figure 6.8

28. Transition
Between glycolysis and the citric acid cycle, pyruvate is oxidized (loses electrons) while a molecule of NAD+ is reduced (gains electrons) to NADH.

29. 6.9 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules
In the citric acid cycle, the two-carbon acetyl part of acetyl CoA is oxidized
Acetyl CoA
CoA
CoA 2
CO2
CITRIC ACID CYCLE 3
NAD
FADH2
FAD 3
NADH 
3 H
ATP
ADP  P
Figure 6.9A

30. The two carbons are added to a four-carbon compound, forming citrate
Which is then degraded back to the starting compound

31. For each turn of the cycle Two CO2 molecules are released
The energy yield is one ATP, three NADH, and one FADH2
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate 1
Citrate
NADH
 H 5
NAD
CO2
leaves cycle
CITRIC ACID CYCLE 2
NAD
Malate
NADH
 H
ADP  P
FADH2 4
ATP
Alpha-ketoglutarate
FAD 3
CO2
leaves cycle
Succinate
NADH
 H
NAD
Step 1
Steps 2
and 3
Steps 4
and 5
Acetyl CoA stokes the furnace.
NADH, ATP, and CO2 are generated during redox reactions.
Redox reactions generate FADH2 and NADH.
Figure 6.9B

32. Citric Acid Cycle
The enzymes of the citric acid cycle are located in the mitochondrial matrix.
At the end of the citric acid cycle, most of the energy remaining from the original glucose is stored in NADH.

33. 6.10 Most ATP production occurs by oxidative phosphorylation
6.10 Most ATP production occurs by oxidative phosphorylation
Electrons from NADH and FADH2
Travel down the electron transport chain to oxygen, which picks up H+ to form water
Energy released by the redox reactions
Is used to pump H+ into the space between the mitochondrial membranes
Overview

34. Electron Transport Chain
In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes driving the synthesis of ATP.
In the electron transport chain, the final electron acceptor is an oxygen atom.
Electron Transport Chain . H+ H+ H+ H+ H+
Protein complex H+ H+
ATP synthase
Electron carrier H+ H+
Intermembrane space
Inner mitochondrial membrane
Electron flow
FADH2
FAD 1
NADH
NAD+ O2
+ 2 H+ 2 H+ H+
Mitochondrial matrix  P
ATP H+
ADP
H2O H+
Electron Transport Chain
Chemiosmosis
OXIDATIVE PHOSPHORYLATION
Figure 6.10

35. CONNECTION
6.11 Certain poisons interrupt critical events in cellular respiration
Various poisons
Block the movement of electrons
Block the flow of H+ through ATP synthase
Allow H+ to leak through the membrane
Rotenone is a poison commonly added to insecticides. Insects exposed to rotenone will die because of inadequate ATP production.
Figure 6.11

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

37. OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
6.12 Review: Each molecule of glucose yields many molecules of ATP
Oxidative phosphorylation, using electron transport and chemiosmosis
Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration
Electron shuttle across membrane
Mitochondrion
Cytoplasm 2
NADH 2
NADH
(or 2 FADH2) 2
NADH 6
NADH 2
FADH2
GLYCOLYSIS
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) 2
2 Acetyl CoA
Glucose
CITRIC ACID CYCLE
Pyruvate
 2 ATP
 2 ATP
 about 34 ATP
by substrate-level phosphorylation
by substrate-level phosphorylation
by oxidative phosphorylation
About 38 ATP
Maximum per glucose:
Figure 6.12

38. Review
Glycolysis and the citric acid cycle must occur two times per glucose molecule.
The energy yield from the complete aerobic breakdown of a single molecule of glucose can vary with the mechanism used to shuttle NADH electrons into the mitochondrion.

39. 6.13 Fermentation is an anaerobic alternative to cellular respiration
6.13 Fermentation is an anaerobic alternative to cellular respiration
Cellular respiration produces the most ATP per molecule of glucose oxidized.
Under anaerobic conditions, many kinds of cells
Can use glycolysis alone to produce small amounts of ATP

40. Found in muscle cells and food products.
In lactic acid fermentation NADH is oxidized to NAD+ as pyruvate is reduced to lactate
Found in muscle cells and food products. 2
NAD 2
NADH 2
NADH 2
NAD
GLYCOLYSIS
2 ADP  2 P 2
ATP
2 Pyruvate
2 Lactate
Glucose
Figure 6.13A

41. Used in brewing, baking, and winemaking.
In alcohol fermentation, NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol
Used in brewing, baking, and winemaking. 2
NAD 2
NADH 2
NADH 2
NAD
GLYCOLYSIS
2 ADP  2 P 2
CO2 2
ATP
released
Glucose
2 Pyruvate
2 Ethanol
Figure 6.13B
Figure 6.13C

42. Strict Anaerobes-require anaerobic conditions and are poisoned by oxygen.
Facultative Anaerobe-can make ATP either by fermentation or oxidative phosphorylation, depending on whether O2 is available.

43. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS
6.14 Cells use many kinds of organic molecules as fuel for cellular respiration

44. OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Carbohydrates, fats, and proteins can all fuel cellular respiration when they are converted to molecules that enter glycolysis or the citric acid cycle
Fats yield the most ATP.
Food, such as peanuts
Carbohydrates
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
CITRIC ACID CYCLE
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Glucose
G3P
Pyruvate
Acetyl CoA
GLYCOLYSIS
ATP
Figure 6.14

45. 6.15 Food molecules provide raw materials for biosynthesis
6.15 Food molecules provide raw materials for biosynthesis
Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials
Biosynthesis consumes ATP
ATP needed to drive biosynthesis
ATP
CITRIC
ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Fatty
acids
Glycerol
Sugars
Proteins
Fats
Carbohydrates
Cells, tissues, organisms
Figure 6.15

46. 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, but not animals
Can also make these molecules from inorganic sources by the process of photosynthesis
Figure 6.16