1. How Cells Harvest Chemical Energy Biofix: Cellular Respiration
Chapter 6
How Cells Harvest Chemical Energy
Biofix: Cellular Respiration

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.
Slow twitch – associated with long distance runners
Fast twitch – associated with sprinters

3. The different types of muscle fibers function either:
The different types of muscle fibers function either:
Aerobically (with oxygen)
Slow twitch muscle groups
Produces lots of ATP
Anaerobically, without oxygen
Fast twitching muscle groups
Produces very little ATP
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
Cellular respiration makes ATP and consumes O2 during the oxidation of glucose to CO2 and H2O
Glucose + O2→ ATP + H2O + CO2

5. To produce glucose and O2 from CO2 and H2O
Photosynthesis uses solar energy
To produce glucose and O2 from CO2 and H2O
CO2
H2O
Glucose O2
ATP
ECOSYSTEM
Sunlight energy
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
(for cellular work)
Heat energy +
Plants, Algae and some photo-
synthetic bacteria and protist
Perform photosynthesis.
The stored energy from glucose
can then be used to do work when
it is converted to ATP.
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.
CO2 O2
Bloodstream
Muscle cells carrying out
Cellular Respiration
Breathing
Glucose + O2
CO2 +H2O +ATP
Lungs
Figure 6.2

7. Breathing and Cellular Respiration are Closely Linked.
Oxygen is required to burn (metabolize) food.
The glucose obtained can than be transformed into ATP – the molecular “fuel” required to do work in an organism.
The mitochondria in muscles used O2 to convert glucose into ATP through a series of steps.

8. The combined effort of the muscular system, respiratory system and circulatory system work to bring reactants to the cell and remove waste products:
Glucose + O2→ ATP + H2O + CO2
Exits the cell and is released into the atmosphere

9. 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
The Balanced Chemical Equation summarizing cellular respiration:
C6H12O6
CO2 6
H2O
ATPs
Glucose
Oxygen gas
Carbon dioxide
Water
Energy O2 +
Figure 6.3

10. Cellular Respiration can produce up to 38 ATP from 1 glucose molecule!
40% of the energy in glucose is converted to ATP
The remaining is lost in the form of heat (2nd Law of Thermodynamics)
Does this sound very efficient to you?
The average automobile is only able to convert about 25% of the energy from gasoline to kinetic energy of motion.
How Many Molecules of energy does a cell need?
A working muscle must regenerate 10 million molecules of ATP every second!

11. CONNECTION
6.4 The human body uses energy from ATP for all its activities
ATP powers almost all cellular and body activities
Energy is required for
breathing, digesting
food, temperature
regulation and blood
circulation!
Table 6.4

12. 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
Energy available to do work is contained in the arrangement of electrons in chemical bonds.
During cellular respiration electrons are transferred.
As electrons are transferred they lose potential energy.
The energy released can then be stored as ATP.

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

14. Redox Reaction
The movement of electrons from one molecule to another is called:
Oxidation-reduction reaction or REDOX
Oxidation is the loss of electrons
Reduction is the gain of elections

15. Electron Transport Chain
The electron transport chain:
The energy staircase
H2O
NAD+
NADH
ATP H+
Controlled release of energy for synthesis of ATP
Electron transport chain 2 O2
2e + 1
The electron transport
chain involves a series
of oxidation-reduction
reactions. With the final
products being water and
lots of ATP.

16. STAGES OF CELLULAR RESPIRATION AND FERMENTATION
6.6 Overview: Cellular respiration occurs in three main stages.
1. Glycolysis
2. Citric Acid Cycle (Krebs)
3. Oxydation-Phosphorylation

17. Stage 1: Glycolysis Occurs in the cytoplasm
Stage 1: Glycolysis
Occurs in the cytoplasm
Breaks down glucose into 2 molecules of pyruvate, producing a small amount of ATP (2)

18. Stage 2: The citric acid cycle (Krebs)
Stage 2: The citric acid cycle (Krebs)
Takes place in the mitochondrial matrix
Completes the breakdown of pyruvate to CO2 .
During the citric acid cycle the following are produced:
2 NADH + H+
FADH2
2 molecules of CO2
1 molecule ATP
Supplies the third stage of cellular respiration with electrons

19. Stage 3: Oxidative phosphorylation – involves the electron transport chain and chemiosmosis.
Occurs in the mitochondria
NADH and FADH2 shuttle electrons to the transport chain (i.e. they are electron carriers)
Uses the energy released by “falling” electrons to pump H+ across a membrane.
Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP from ADP.

20. ATP synthesis can occur by two mechanism:
1. Substrate level phosphorylation:
the addition of a phosphate to ADP from an intermediate of glycolysis or the citric acid cycle (Model 6.7)
2. Oxidation –Phosphorylation:
electrons from the electron transport chain generate a chemiosmotic gradient that can drive the synthesis of ATP.
Chemiosmosis :
the electron transport chain generates a chemical gradient when H+ across the mitochondrial membrane. This gradient drives the diffusion of H+ through a protein enzyme ,ATP Synthase – producing ATP.

21. An overview of cellular respiration
An overview of cellular respiration
NADH
FADH2
GLYCOLYSIS
Glucose
Pyruvate
CITRIC ACID CYCLE
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Substrate-level phosphorylation
Oxidative phosphorylation
Mitochondrion
and
High-energy electrons carried by NADH
ATP
CO2
Cytoplasm
Figure 6.6

22. 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
In glycolysis, ATP is used to prime a glucose molecule
Which is split into two molecules of pyruvate
Web: Glycolysis
NAD+
NADH H+
Glucose
2 Pyruvate
ATP 2 P
2 ADP +
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
Adenosine
Organic molecule (substrate)
ADP
ATP 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
 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 P P
Glyceraldehyde-3-phosphate (G3P)
 Step     A redox reaction generates NADH. 5 6 9
NAD  5
NAD 
ENERGY PAYOFF PHASE
NADH P 6
NADH P 6
+H
+H P P P P
1,3 -Diphosphoglycerate
 Steps     –      ATP and pyruvate are produced. 6 9
ADP
ADP 6 7 7
ATP
ATP P P
3 -Phosphoglycerate 7 P P 8 8
2-Phosphoglycerate
Note the net gain of
ATP. How efficient do you
think this is? 8
H2O
H2O P P
Phosphoenolpyruvate (PEP)
ADP 9
ADP 9 9
ATP
ATP
Pyruvate
Figure 6.7C

26. Acetyl CoA (acetyl coenzyme A)
6.8 Pyruvate is chemically groomed for the citric acid cycle
The Citric Acid (Krebs) Cycle
Prior to the citric acid cycle
Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA
CO2
Pyruvate
NAD+
NADH
+ H+
CoA
Acetyl CoA (acetyl coenzyme A)
Coenzyme A
Figure 6.8 2 1 3

27. 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
CoA
CO2
NAD+
NADH
FAD
FADH2
ATP P
CITRIC ACID CYCLE
ADP + 3 +
3 H+
Acetyl CoA 2
The two carbons are added to four-carbon compound, forming citrate which is then degraded back to the starting compound.
Figure 6.9A

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

29. 6.10 Most ATP production occurs by oxidative phosphorylation
6.10 Most ATP production occurs by oxidative phosphorylation
6D Electron Transport and Chemiosmosis
The Electron transport chain is a series of proteins built into the cristae of the mitochondria.
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

30. Driving the synthesis of ATP
In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes
Driving the synthesis of ATP
Intermembrane space
Inner mitochondrial membrane
Mitochondrial matrix
Protein complex
Electron flow
Electron carrier
NADH
NAD+
FADH2
FAD
H2O
ATP
ADP
ATP synthase H+ + P O2
Electron Transport Chain
Chemiosmosis .
OXIDATIVE PHOSPHORYLATION
+ 2 1 2
Figure 6.10

31. Cyanide, carbon monoxide
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 H+ O2
H2O P
ATP
NADH
NAD+
FADH2
FAD
Rotenone
Cyanide, carbon monoxide
Oligomycin
DNP
ATP Synthase + 2
ADP
Electron Transport Chain
Chemiosmosis 1
Figure 6.11

32. 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)
Glucose 2
2 Acetyl CoA
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

33. 6.13 Fermentation is an anaerobic alternative to cellular respiration
6.13 Fermentation is an anaerobic alternative to cellular respiration
Web: Fermentation
Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP.

34. Have you ever had sore muscles?
During glycolosis NAD+ → NADH.
To continue harvesting energy NAD+ must be regenerated. Under normal aerobic conditions this is not a problem.
Your muscles (and a few other types of cells) regenerate NAD+ by a process called lactic acid fermentation.
The lactate may build up in the muscles causing the soreness. Over time the lactate is taken to the liver where it can be converted back into pyruvate.

35. In lactic acid fermentation
In lactic acid fermentation
NADH is oxidized to NAD+ as pyruvate is reduced to lactate
2 Lactate
NAD+
NADH 2
ATP
2 ADP + 2
2 Pyruvate
GLYCOLYSIS P
Glucose
Figure 6.13A

36. In alcohol fermentation
In alcohol fermentation
NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol
NAD+
NADH 2
GLYCOLYSIS
2 ADP + 2 P
ATP
Glucose
2 Pyruvate
released
CO2
2 Ethanol
Figure 6.13B
Figure 6.13C

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

38. 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
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Food, such as peanuts
Carbohydrates
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
Glucose
G3P
Pyruvate
Acetyl CoA
CITRIC ACID CYCLE
ATP
GLYCOLYSIS
Figure 6.14

39. 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 (e.g. amino acids are recycled to build proteins)
This process of 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
Carbohydrates
Fats
Proteins
Cells, tissues, organisms
Figure 6.15

40. 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