1. How Cells Harvest Chemical Energy
Chapter 6

2. INTRODUCTION TO CELLULAR RESPIRATION

3. Photosynthesis and Cellular Respiration Provide Energy For Life
Energy that supports life on Earth is captured from sun and used for plant, algae, protist, and bacterial photosynthesis
Photosynthesis produces sugar and oxygen.
Other organisms use the energy in sugar and O2 from the atmosphere in cellular respiration
Cellular respiration releases CO2 and H2O
Together, these two processes are responsible for the majority of life on Earth

4. Sunlight energy Photosynthesis in chloroplasts + + (for cellular work)
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2
Glucose + +
H2O O2
Cellular respiration
in mitochondria
Figure 6.1 The connection between photosynthesis and cellular respiration.
ATP
(for cellular work)
Heat energy

5. Breathing and cellular respiration are closely related
Breathing Supplies Oxygen to Our Cells For Use in Cellular Respiration and Removes Carbon Dioxide
Breathing and cellular respiration are closely related
Breathing is necessary for exchange of CO2 produced during cellular respiration for atmospheric O2
Cellular respiration uses O2 and produces CO2

6. Muscle cells carrying out
Breathing O2
CO2
Lungs
CO2 O2
Bloodstream
Figure 6.2 The connection between breathing and cellular respiration.
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP

7. Cellular Respiration Banks Energy in ATP Molecules
Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to ATP molecules.
Cellular respiration produces up to 38 ATP/glucose molecule
Other foods (organic molecules) can be used as a source of energy in addition to glucose
C6H12O6
+ 6 O2 6
CO2
+ 6
H2O +
ATPs
Glucose
Oxygen
Carbon
dioxide
Water
Energy
Figure 6.3 Summary equation for cellular respiration: C6H12O6 + 6 O2 6 CO2 + H2O + energy

8. Cells Tap Energy From Electrons “falling” From Organic Fuels to Oxygen
When bonds of glucose are broken, its electrons are transferred to oxygen (oxygen is electronegative, and pulls e- towards it)
Cellular respiration is the controlled breakdown of organic molecules as electrons are removed from a fuel source and transferred to oxygen
As electrons pass down the ETC, energy is released in small amounts, and ultimately stored in ATP

9. NADH ATP NAD+ + 2e– Controlled release of H+ energy for synthesis
of ATP H+
Electron transport
chain
Figure 6.5C In cellular respiration, electrons fall down an energy staircase and finally reduce O2.
2e– H+ 1  2 O2
H2O

10. Cells Tap Energy From Electrons “falling” From Organic Fuels to Oxygen
The cellular respiration equation explained:
Glucose loses electrons (in the form of hydrogen) to oxygen and is converted to CO2
Glucose is oxidized
Oxygen gains electrons (in the form of hydrogens) from glucose and is converted to H2O
Oxygen is reduced
The reducing agent = The molecule carrying the hydrogens (with e-) (NADH, FADH2)
The oxidizing agent= The molecule that receives the hydrogens (is without e-) (NAD+, FAD)

11. C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy Glucose (ATP)
Loss of hydrogen atoms
(oxidation)
C6H12O O2
6 CO H2O Energy
Glucose
(ATP)
Gain of hydrogen atoms
(reduction)
Figure 6.5A Rearrangement of hydrogen atoms (with their electrons) in the redox reactions of cellular respiration.

12. Enzymes are necessary to Oxidize Glucose and Other Foods
Dehydrogenase enzymes remove hydrogens from organic molecules and transfer them to electron acceptors
Oxidation
Dehydrogenase
Figure 6.5B A pair of redox reactions, occurring simultaneously.
Reduction + H+
NAD+
+ 2 H
NADH
(carries
2 electrons)
2 H e–

13. Cells tap energy from electrons “falling” from organic fuels to Oxygen
The electron acceptor is a coenzyme called NAD+ (nicotinamide adenine dinucleotide)
Another coenzyme that functions like NAD+ is FAD
They “carry” e- from glucose to a series of proteins found along the cristae of the mitochondria called the electron transport chain or ETC
Copyright © 2009 Pearson Education, Inc.

14. STAGES OF CELLULAR RESPIRATION AND FERMENTATION

15. Cellular respiration occurs in three main stages
Stage 1: Glycolysis
Occurs in the cytoplasm
What happens ?: A single molecule of glucose is enzymatically cut in half through a series of steps to produce two molecules of pyruvate
In addition to Pyruvate:
Two molecules of NADH are formed (when two molecules of NAD+ are reduced)
Two molecules of ATP are produced by substrate-level phosphorylation

16. Substrate-level Phosphorylation
Substrate level phosphorylation is when an enzyme transfers a phosphate group from a substrate molecule to ADP, forming ATP
Enzyme
Enzyme + P
ADP
Figure 6.7B Substrate-level phosphorylation: transfer of a phosphate group P from a substrate to ADP, producing ATP.
ATP P P
Substrate
Product

17. Figure 6.7C Details of glycolysis.
ENERGY INVESTMENT
PHASE
Glucose
ATP
Steps – A fuel molecule is energized,
using ATP. 1 3
Step 1
ADP P
Glucose-6-phosphate 2 P
Fructose-6-phosphate
ATP 3
ADP P P
Step A six-carbon intermediate splits
Into two three-carbon intermediates.
Fructose-1,6-bisphosphate 4 4 P P
Glyceraldehyde-3-phosphate
(G3P)
Step A redox reaction
generates NADH. 5
NAD+ 5
NAD+ 5
ENERGY PAYOFF PHASE
NADH P
NADH P
+ H+
+ H+ P P P P
1,3-Bisphosphoglycerate
ADP
ADP 6 6
ATP
ATP
Figure 6.7C Details of glycolysis. P P
3-Phosphoglycerate 7 7
Steps – ATP and pyruvate
are produced. 6 9 P P
2-Phosphoglycerate 8 8
H2O
H2O P P
Phosphoenolpyruvate
(PEP)
ADP
ADP 9 9
ATP
ATP
Pyruvate

18. Pyruvate is chemically groomed for the citric acid cycle
The Grooming of Pyruvate:
Location: mitochondrial matrix
Purpose: to prepare pyruvate for entry into Kreb’s cycle
What Happens:
1. The removal of a carboxyl group (decarboxylation) which is
released as CO2
2. The remaining 2-carbon fragment is oxidized into acetate
NAD+ accepted the electrons forming NADH
3. Coenzyme A binds to the 2-carbon acetate
forming acetyl coenzyme A
Products: CO2 , NADH and Acetyl CoA

19. NAD+ NADH  H+ 2 CoA Pyruvate 1 Acetyl coenzyme A 3 CO2 Coenzyme A
Figure 6.8 The conversion of pyruvate to acetyl CoA.
Coenzyme A

20. Cellular respiration occurs in three main stages
Stage 2: The Kreb’s Cycle (citric acid cycle)
Location: mitochondrial matrix
Purpose: further breakdown of what remains of glucose into CO2 ; to form electron carriers NADH, FADH2
What Happens: 2-C acetate combines with 4-C oxaloacetate forming 6-C citrate
6-C citrate then passes through a series of redox reactions that regenerate oxaloacetate (4-C molecule )
Products from one turn of the cycle: 3 NADH, 1 FADH2 , 1 ATP, 2 CO2
Products per glucose: 6 NADH, 2 FADH2 , 2 ATP, 4 CO2

21. CITRIC ACID CYCLE Acetyl CoA CoA CoA 2 CO2 3 NAD+ FADH2 FAD 3 NADH 
Figure 6.9A An overview of the citric acid cycle: Two carbons enter the cycle through acetyl CoA, and 2 CO2, 3 NADH, 1 FADH2, and 1 ATP exit the cycle.
FAD 3
NADH 
3 H+
ATP
ADP + P

22. CITRIC ACID CYCLE Acetyl CoA 2 carbons enter cycle Oxaloacetate1
Citrate
NADH
+ H+
NAD+ 5
NAD+
NADH
+ H+ 2
CITRIC ACID CYCLE
Malate
CO2
leaves cycle
ADP  P
FADH2 4
ATP
Alpha-ketoglutarate
Figure 6.9B Details of the citric acid cycle.
FAD 3
CO2
leaves cycle
Succinate
NAD+
NADH
+ H+
Step
Acetyl CoA stokes the furnace. 1
Steps –
NADH, ATP, and CO2 are generated
during redox reactions. 2 3
Steps –
Redox reactions generate FADH2
and NADH. 4 5

23. Cellular respiration occurs in three main stages
Stage 3: Oxidative phosphorylation (aka the ETC)
Location: cristae of mitochondrion
Purpose: to generate a proton gradient that is used to form ATP
What Happens: Electrons are supplied by NADH & FADH2 , then passed along the proteins of the ETC. As e- are passed from protein to protein they pump H+ into the intermembrane space
The potential energy of this proton gradient is used to make ATP by chemiosmosis
The concentration gradient drives H+ through ATP synthases producing ATP
The ETC + chemiosmosis = oxidative phosphorylation
Products: ATP/glucose

24. OXIDATIVE PHOSPHORYLATION
Protein
complex
of electron
carriers H+ H+
Electron
carrier H+ H+
ATP
synthase
Intermembrane
space
Inner
mitochondrial
membrane
FADH2
FAD
Electron
flow
NADH
NAD+ 2  1 O2
+ 2 H+ H+
Mitochondrial
matrix H+
Figure 6.10 Oxidative phosphorylation, using electron transport and chemiosmosis in the mitochondrion.
ADP + P H+
ATP
H2O H+
Electron Transport Chain
Chemiosmosis
OXIDATIVE PHOSPHORYLATION

25. by oxidative phosphorylation
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
Figure 6.12 An estimated tally of the ATP produced by substrate-level and oxidative phosphorylation in cellular respiration.
by substrate-level
phosphorylation
by substrate-level
phosphorylation
by oxidative phosphorylation
About
38 ATP
Maximum per glucose:

26. Fermentation enables cells to produce ATP without oxygen
Fermentation is an anaerobic (without oxygen) energy-generating process
Includes glycolysis, and the regeneration of NAD+
Purpose: to produce ATP in the absence of oxygen
What Happens?: NADH is oxidized to NAD+ when pyruvate is reduced to lactate
Pyruvate serves as an “electron sink,” a place to dispose of the electrons generated by oxidation reactions in glycolysis
Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation
Copyright © 2009 Pearson Education, Inc.

27. Lactic Acid Fermentation Steps to regenerate NAD+
Glucose 2
NAD+
2 ADP  2 P
GLYCOLYSIS
Glycolysis 2
ATP 2
NADH
Lactic Acid Fermentation
2 Pyruvate 2
NADH
Steps to regenerate NAD+
Figure 6.13A Lactic acid fermentation oxidizes NADH to NAD+ and produces lactate. 2
NAD+
2 Lactate
Lactic acid fermentation

28. Fermentation enables cells to produce ATP without oxygen
The baking and winemaking industry have used alcohol fermentation for thousands of years
Happens in yeast cells (single-celled fungi)
They convert pyruvate to CO2 and ethanol while oxidizing NADH back to NAD+

29. Steps to regenerate NAD+ with a release of CO2
Glucose
2 ADP 2
NAD+  2 P
GLYCOLYSIS
Glycolysis 2
ATP 2
NADH
Alcohol Fermentation
2 Pyruvate 2
NADH 2
CO2
Steps to regenerate NAD+ with a release of CO2
released
Figure 6.13B Alcohol fermentation oxidizes NADH to NAD+ and produces ethanol and CO2. 2
NAD+
2 Ethanol
Alcohol fermentation

30. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS

31. Cells use many kinds of organic molecules as fuel for cellular respiration
Although glucose is considered the primary source of sugar for respiration and fermentation, there are actually three sources of molecules for generation of ATP
Carbohydrates (disaccharides)
Proteins (after conversion to amino acids)
Fats

32. Food, such as peanuts Carbohydrates Fats Proteins Sugars Glycerol
Fatty acids
Amino acids
Amino
groups
Figure 6.15 Pathways that break down various food molecules.
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC
ACID
CYCLE
Acetyl
CoA
Glucose
G3P
Pyruvate
GLYCOLYSIS
ATP

33. ATP needed to drive biosynthesis
GLUCOSE SYNTHESIS
CITRIC
ACID
CYCLE
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Fatty acids
Glycerol
Sugars
Proteins
Fats
Carbohydrates
Figure 6.16 Biosynthesis of large organic molecules from intermediates of cellular respiration.
Cells, tissues, organisms

34. Cellular respiration ATP (a) (b) (d) (c) (f) (e) generates
has three stages
oxidizes
uses
ATP
(a)
produce
some
C6H12O6
(b)
(d)
produces
many
energy for
to pull
electrons down to
(c)
(f)
by process called
uses
H+ diffuse
through
ATP synthase
(e)
uses
pumps H+ to create