1. FIGHTING ENTROPY II: RESPIRATION
BIO 2, Lecture 13
FIGHTING ENTROPY II:
RESPIRATION

2. $10,000 bill (Starch; Unusable)
Respiration is the process whereby cells break down complex organic molecules (like starch) and convert them into ATP + heat (not 100% efficient)
The cell then uses the ATP to do work
$10,000 bill (Starch; Unusable)
$1 bills
(ATP; Usable)

3. There are two types of respiration:
Anaerobic respiration, also called fermentation, occurs without O2
Example: Ethanol fermentation of glucose
C6H12O6 + ADP + Pi  2 C2H5OH + 2 CO2 + ATP + heat
Aerobic respiration relies on O2
Is more efficient than anaerobic respiration; generates more ATP per organic molecule, loses less energy as heat
C6H12O6 + 6O2 + ADP + Pi  6CO2 + 6H2O + ATP heat

4. Cells do three types of work: mechanical, transport, and chemical
All must be coupled to the hydrolysis of ATP
Overall, the coupled reactions are catabolic
An example is the creation of the amino acid glutamine from ammonia and glutamic acid
Figure14.2 Crossing pea plants

5. (b) Coupled with ATP hydrolysis, a catabolic (exergonic) reaction
Ammonia displaces
the phosphate group,
forming glutamine.
(a) Anabolic (endergonic) reaction
(c) Overall free-energy change P
Glu
NH3
NH2 i
ADP +
ATP
ATP phosphorylates
glutamic acid,
making the amino
acid less stable.
Glutamic
acid
Glutamine
Ammonia
∆G = +3.4 kcal/mol 2 1
Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis

6. Adenine Phosphate groups Ribose
Figure 8.8 The structure of adenosine triphosphate (ATP)
Ribose

7. Energy is released from ATP when the terminal phosphate bond is broken
The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis
Energy is released from ATP when the terminal phosphate bond is broken
Inorganic phosphate
Energy
Adenosine triphosphate (ATP)
Adenosine diphosphate (ADP) P +
H20 i

8. ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP)
The energy to re-phosphorylate ADP comes from catabolic reactions in the cell P i
ADP +
Energy from
catabolism (exergonic,
energy-releasing
processes)
Energy for cellular work
(endergonic, energy-
consuming processes)
ATP
H2O

9. Although carbohydrates, fats, and proteins can all be broken down during respiration to produce ATP, it is helpful to trace cellular respiration with the sugar glucose
The step-wise transfer of electrons (from high energy states in complex organic molecules to lower energy states in simple organic molecules) gently releases the energy stored in glucose to regenerate ATP from ADP + P
Figure 14.3 When F1 hybrid pea plants are allowed to self-pollinate, which traits appear in the F2 generation?

10. In oxidation, a substance loses electrons, or is oxidized
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
In oxidation, a substance loses electrons, or is oxidized
In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
Figure 13.6b Three types of sexual life cycles—plants and some algae

11. becomes oxidized
(loses electron)
becomes reduced
(gains electron)

12. Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds, thereby changing the potential chemical energy stored in the molecules
Reduced organic molecules carry more potential chemical energy than oxidized forms of the same molecules
Starch is a highly reduced form of water and carbon dioxide
Therefore, breaking starch down into water and carbon dioxide releases energy

13. Reactants Products becomes oxidized becomes reduced Methane Oxygen
Figure 9.3 Methane combustion as an energy-yielding redox reaction
Methane
Oxygen
Carbon dioxide
Water

14. During cellular respiration, the fuel (such as glucose) is oxidized, and another molecule (such as O2) is reduced
The chemical potential energy in the reactants is greater than the chemical potential energy in the products; thus energy is released
becomes oxidized
becomes reduced

15. Both anaerobic and aerobic respiration begin with glycolysis
Breaks down glucose into two molecules of pyruvate) to produce 2 ATP per glucose
Takes place in the cytoplasm
In anaerobic respiration, the process stops here and only 2 ATP are generated per glucose

16. Both steps take place in the mitochondria
Aerobic respiration has two additional steps that break down the pyruvate to carbon dioxide and water to produce an additional 36 ATP
The citric acid cycle (completes the breakdown of glucose)
Oxidative phosphorylation (accounts for most of the ATP synthesis)
Both steps take place in the mitochondria

17. Glycolysis (“splitting of sugar”) has two major phases:
Energy investment phase
Energy payoff phase
In the energy investment phase, 2 ATP are consumed to “kick start” the process
In the energy payoff phase, four ATP are produced, yielding a net gain of 2 ATP

18. Energy investment phase
Glucose
2 ADP + 2 P
2 ATP
used
formed
4 ATP
Energy payoff phase
4 ADP + 4
2 NAD e– + 4 H+
2 NADH
+ 2 H+
2 Pyruvate + 2 H2O
Net
4 ATP formed – 2 ATP used
2 NADH + 2 H+
Figure 9.8 The energy input and output of glycolysis

19. The energy stored in NADH is likewise wasted
In anaerobic respiration, the process stops with the production of 2 ATP
Pyruvate is converted to waste products (like ethanol) but no more ATP is gained
The energy stored in NADH is likewise wasted
It is important to note, however, that NADH carries high energy electrons and can be harvested to produce ATP if a cell has the machinery to do so ...

20. Potential source of additional ATP; WASTED in aerobic respiration
Anaerobic Respiration
Substrate-level
phosphorylation
ATP
Cytosol
Glucose
Pyruvate
Glycolysis
Electrons
carried
via NADH
Net = 2
Net = 2 NADH
Potential source of additional ATP; WASTED in aerobic respiration
Figure 9.6 An overview of cellular respiration

21. The energy stored in NADH is likewise wasted
In anaerobic respiration, the process stops with the production of 2 ATP
Pyruvate is converted to waste products (like ethanol) but no more ATP is gained
The energy stored in NADH is likewise wasted
It is important to note, however, that NADH carries high energy electrons and can be harvested to produce ATP if a cell has the machinery to do so ...

22. Takes place in cells that have mitochondria
Aerobic respiration continues the process of glycolysis to breakdown pyruvate and utilize the high energy electrons stored in NADH
Takes place in cells that have mitochondria
The citric acid cycle (breaks down pyruvate to CO2 and H2O in the mitochondrial matrix to produce additional ATP, NADH, and FADH2)
Oxidative phosphorylation (harvests electrons from NADH and FADH2 in the inner mitochondrial membrane and accounts for most of the ATP synthesis)

23. Electrons carried via NADH Electrons carried via NADH and FADH2
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Mitochondrion
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation

24. Electrons carried via NADH Electrons carried via NADH and FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Mitochondrion
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation

25. The Citric Acid Cycle:
In the presence of O2, pyruvate (generated by glycolysis) enters the mitochondrion from the cytoplasm
Prior to the start of the cycle, pyruvate is converted to acetyl CoA, generating one molecule of NADH
The cycle then oxidizes acetyl CoA, generating 1 ATP, 3 NADH, and 1 FADH2 per turn

26. Pyruvate NAD+ NADH + H+ Acetyl CoA CO2 CoA Citric acid cycle FADH2 FAD3
3 NAD+
+ 3 H+
ADP + P i
ATP
Figure 9.11 An overview of the citric acid cycle

27. The cycle is “fed” by acetyl-coA
In the first step, the acetyl-coA is combined with oxaloacetate to form citrate
The citrate is then broken down in a series of steps to produce energy (in the form of ATP, NADH, and FADH2) + CO2 (gas)
The end product of the cycle is oxaloacetate, which can then combine with another molecule of acetyl-coA to run the cycle again ...

28. Succinyl CoA Citric acid cycle
Acetyl CoA
CoA—SH
Citrate
H2O
Isocitrate
NAD+
NADH
+ H+
CO2
-Keto-
glutarate
Succinyl
CoA P i
GTP
GDP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
Citric
acid
cycle
Malate
Oxaloacetate
+H+ 1 2 3 4 5 6 7 8
Figure 9.12 A closer look at the citric acid cycle

29. Following glycolysis and the citric acid cycle, NADH and FADH2 carry most of the energy extracted from food
These two molecules transport the high energy electrons generated by the breakdown of glucose to pyruvate (during glycolysis) and pyruvate to oxaloacetate and CO2 (during the citric acid cycle) and donate them to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

30. The electron transport chain is located in the inner membrane of the mitochondrion
Most of the chain’s components are proteins, which exist in multi-protein complexes
The carriers alternate reduced and oxidized states as they accept (become reduced) and donate (become oxidized) electrons down the chain
Electrons drop in free energy as they go down the chain and are finally passed to O2 (gas), forming H2O

31. Free energy (G) relative to O2 (kcal/mol)
NADH
NAD+ 2
FADH2
FAD
Multiprotein
complexes
Fe•S
FMN Q 
Cyt b 

Cyt c1
Cyt c
Cyt a
Cyt a3 IV
Free energy (G) relative to O2 (kcal/mol) 50 40 30 20 10
(from NADH
or FADH2)
2 H+ + 1/2 O2
H2O e–
Figure 9.13 Free-energy change during electron transport

32. As electrons are transferred down the electron transport chain, the energy released at each step is used by the protein complexes to pump H+ from the mitochondrial matrix to the inter-membrane space
H+ then moves back across the membrane, with its diffusion gradient, passing through channels in a protein complex called ATP synthase

33. ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP from ADP and Pi
This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work
The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work

34. Why we breathe O2!! Protein complex of electron carriers H+ Cyt c Q 
 V
FADH2
FAD
NAD+
NADH
(carrying electrons
from food)
Electron transport chain
2 H+ + 1/2O2
H2O
ADP + P i
Chemiosmosis
Oxidative phosphorylation
ATP synthase
ATP 2 1
Why we breathe O2!!
Figure 9.16 Chemiosmosis couples the electron transport chain to ATP synthesis

35. During aerobic respiration, most energy flows in this sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
About 40% of the energy in a glucose molecule is transferred to ATP during aerobic respiration, generating about 38 ATP
The rest is lost as heat

36. Anaerobic phase Aerobic phase Citric acid cycle MITOCHONDRION
Maximum per glucose:
About
38 ATP
+ 2 ATP
+ about 34 ATP
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Citric
acid
cycle 2
Acetyl
CoA
Glycolysis
Glucose
Pyruvate
2 NADH
6 NADH
2 FADH2
CYTOSOL
Electron shuttles
span membrane or
MITOCHONDRION
Anaerobic phase
Aerobic phase
Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration

37. Comparing aerobic and anaerobic respiration:
Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate
However, the processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration
Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

38. Respiration can use many different fuels (not just glucose!)
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Fatty
Glycolysis
Glucose
Glyceraldehyde-3-
Pyruvate P
NH3
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Respiration can use many different fuels (not just glucose!)
Figure 9.20 The catabolism of various molecules from food

39. (a) Uncontrolled reaction H2O H2 + 1/2 O2
Free energy, G
(a) Uncontrolled reaction
H2O
H2 + 1/2 O2
Explosive
release of
heat and light
energy
(b) Cellular respiration
Controlled
energy for
synthesis of
ATP
2 H e–
2 H +
1/2 O2
(from food)
2 H+
2 e–
Electron transport
chain
Figure 9.5 An introduction to electron transport chains

40. Cellular respiration in mitochondria Organic molecules
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
molecules
+ O2
ATP powers most cellular work
Heat
ATP
Figure 9.2 Energy flow and chemical recycling in ecosystems