1. Photosynthesis and Cellular Respiration
EK2A2: Organisms capture and store free energy for use in biological processes.

2. Redox Reactions Vocabulary
Redox reaction: refers to both reactions together; because an electron transfer requires both a donor and an acceptor, oxidation and reduction go together
Oxidation: refers to the loss of electros
Reduction: refers to the gain of electrons (e- = negative  reduce charge)
Oxidizing agent: causes the oxidation; electron acceptor; must receive e- for a loss to happen
Reducing agent: causes the reduction; electron donor; must give e- for a gain to happen
OILRIG: oxidation is loss, reduction is gain
LEO says GER: loss of electrons oxidation, gain of electrons reduction

3. Why do redox reactions matter to organisms?
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is ultimately used to synthesize ATP
EX: Cellular Respiration
Glucose is oxidized and O2 is reduced
Electrons lose potential eneregy as they move towards O2 e- move towards O2 because it is so electronegative (wants electrons to become more stable) energy is released
becomes oxidized
becomes reduced

4. Pair Share 45 seconds: Redox Rxns:
Explain the difference between oxidation and reductions
What is the difference between oxidizing agent and reducing agent
Why are redox rxns important to living things
What is the oxidizing agent in cellular respiration?
30 seconds: Overview of Cellular Respiration:
What are the three main steps of cellular respiration?
Where do these steps take place?
What are the reactants and products of cellular respiration?
What is the purpose of cellular respiration?

5. Overview of Cellular Respiration
Glycolysis
Citric acid cycle (aka Krebs cycle)
Oxidative phosphorylation: Electron transport chain and chemiosmosis

6. Purpose of Cellular Respiration
Break down organic molecules (usually glucose) to form ATP (ADPATP)
Two main ways to form ATP
Oxidative phosphorylation: 90% of ATP made this way; powered by redox reactions of the electron transport chain; inorganic phosphate is added to ADP by ATP synthase (driven by the chemical gradient created by the ETC)
Substrate-level phosphorylation: enzyme transfers a phosphate group from a substrate to ADP; happens during glycolsis and citric acid cycle
Enzyme
ADP P
Substrate
ATP +
Product

7. An overview of Cellular Respiration Basics
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose
Pyruvate
Glycolysis
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Oxidative
Krebs
Cycle
phosphorylation:
electron transport
and
chemiosmosis

8. NAD+ (Nicotineamide adenine dinuclotide)
Coenzyme that acts as an electron acceptor
Functions as an oxidizing agent during respiration
Traps electrons from glucose and other organic molecules with the help of the enzyme dehydrogenase
Enzyme removes a pair of hydrogen atoms (2 electrons and 2 protons) from the substrate  delivers 2 electrons and 1 proton to its coenzyme (NAD+); other H+ is released into the surrounding solution (this H+ will become important later)
Each NADH represents stored energy that is used to synthesize ATP
Dehydrogenase

9. Details of Glycolysis
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+
Glycolysis means “sugar splitting;” glucose is broken into two molecules of pyruvate
Occurs in the cytoplasm and has two major phases:
Energy investing phase – activation energy is needed to get the exergonic reaction going (2ATP molecules)
Energy payoff phase – ATP and NADH is created
Glucose + 2 ATP (activation energy) pyruvate (Krebs cycle) + ATP (substrate-level) + 2NADH (carries electrons to ETC) + 2 H+ +2H2O

10. Energy investment phase
The
energy
input
and
output of
glycolysis
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

11. A closer look at glycolysis Glucose-6-phosphate 2 Phosphogluco-
ATP 1
Hexokinase
ADP
Glucose-6-phosphate
Glucose-6-phosphate 2
Phosphoglucoisomerase 2
Phosphogluco-
isomerase
Fructose-6-phosphate
Figure 9.9
Fructose-6-phosphate

12. Fructose- 1, 6-bisphosphate
Glucose
ATP 1 1
Hexokinase
ADP
Fructose-6-phosphate
Glucose-6-phosphate 2 2
Phosphoglucoisomerase
ATP 3
Phosphofructokinase: allosteric enzyme
Fructose-6-phosphate
ATP 3 3
ADP
Phosphofructokinase
ADP
Figure 9.9 A closer look at glycolysis
Fructose-
1, 6-bisphosphate
Fructose-
1, 6-bisphosphate

13. Aldolase Isomerase Fructose- 1, 6-bisphosphate 4 5 Dihydroxyacetone
Glucose
ATP 1
Hexokinase
ADP
Glucose-6-phosphate 2
Phosphoglucoisomerase
Fructose-
1, 6-bisphosphate 4
Fructose-6-phosphate
Aldolase
ATP 3
Phosphofructokinase
ADP
Figure 9.9 A closer look at glycolysis 5
Isomerase
Fructose-
1, 6-bisphosphate 4
Aldolase 5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate

14. 2 2 ADP 2 ATP 2 3-Phosphoglycerate 1, 3-Bisphosphoglycerate 7
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
1, 3-Bisphosphoglycerate
2 ADP 2
3-Phosphoglycerate 7
Phosphoglycero-
kinase
2 ATP
Figure 9.9 A closer look at glycolysis 2
3-Phosphoglycerate

15. 2 3-Phosphoglycerate 8 Phosphoglycero- mutase 2 2-Phosphoglycerate
Fig
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
3-Phosphoglycerate 2
3-Phosphoglycerate 8
Phosphoglyceromutase 8
Phosphoglycero-
mutase 2
2-Phosphoglycerate
Figure 9.9 A closer look at glycolysis 2
2-Phosphoglycerate

16. 2 2-Phosphoglycerate Enolase 2 H2O 2 Phosphoenolpyruvate 9
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
2-Phosphoglycerate 2
3-Phosphoglycerate 8
Phosphoglyceromutase 9
Enolase
2 H2O 2
2-Phosphoglycerate 9
Enolase
2 H2O
Figure 9.9 A closer look at glycolysis 2
Phosphoenolpyruvate 2
Phosphoenolpyruvate

17. Pyruvate 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
Phosphoenolpyruvate
2 ADP 2
3-Phosphoglycerate 8 10
Phosphoglyceromutase
Pyruvate kinase
2 ATP 2
2-Phosphoglycerate 9
Enolase
2 H2O
Figure 9.9 A closer look at glycolysis 2
Phosphoenolpyruvate
2 ADP 10
Pyruvate kinase
2 ATP 2
Pyruvate 2
Pyruvate

18. Details of the citric acid cycle
If O2 is present, pyruvate from glycolysis enters the mitochondria
Pyruvate is then converted into Acetyl CoA
In this process CO2 is released into the atmosphere and more NADH is formed (this will carry e- to the ETC)
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+ 2 1 3
Pyruvate
Transport protein
CO2
Coenzyme A
Acetyl CoA

19. Details of the citric acid cycle (continued)
Pyruvate
NAD+
NADH
+ H+
Acetyl CoA
CO2
CoA
Citric
acid
cycle
FADH2
FAD 2 3
3 NAD+
+ 3 H+
ADP + P i
ATP
Citric acid cycle (aka Krebs cycle) take place within the mitochondrial matrix
Cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn (two turns per glucose molecule from glycolysis)
Has eight steps, each catalyzed by a specific enzyme
NADH and FADH2 produced by the Krebs cycle carry electrons extracted from food to the electron transport chain in the mitochondrial cristae membrane
2 additional molecules of CO2 are released (three total; 1 from pyruvate  acetyl Co A)

20. Citric Acid Cycle Acetyl CoA Oxaloacetate OAA Malate Citrate
CoA—SH
NADH
+H+ 1
H2O
NAD+ 8
Oxaloacetate
OAA 2
Malate
Citrate
Isocitrate
NAD+
Citric
Acid
Cycle
NADH 3
+ H+ 7
H2O
CO2
Fumarate
CoA—SH
-Keto-
glutarate
Figure 9.12 4 6
CoA—SH
FADH2 5
CO2
NAD+
FAD
Succinate P
NADH i
GTP
GDP
Succinyl
CoA
+ H+
ADP
ATP

21. Pair Share
At the end of glycolysis and the citric acid cycle…where is the energy that was originally in the glucose molecule???

22. Let’s look at the energy so far
Following glycolysis and the citric acid cycle we have a total of 4 ATP molecules that have been created via substrate- level phosphorylation
2 from glycolysis and 2 from Krebs
Most of the energy extracted from the glucose molecule is currently stored in the Coenzyme carries NADH and FADH2
Some of the energy has been lost as heat
Energy in the NADH and FADH2 is now going to be used in the third step of cellular respiration (electron transport chain)

23. What exactly is the “Electron Transport Chain?
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–
waste
Collection of molecules embedded in the inner membrane of mitochondria in eukaryotic cells (prokaryotes = plasma membrane)
Most components are proteins that exist in multiprotein complexes numbered I through IV

24. Electron Transport Chain
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–
waste
Electron carries alternate between reduced and oxidized states; as electrons move down the chain energy is released
Electrons removed from glucose by NAD+ are transferred from NADH to the first molecule of the electron transport chain in complex I
The last electron acceptor passes its electrons to O2 (which is known as the terminal electron acceptor)
O2 picks up a pair of H+ (hydrogen ions) from the aqueous solution to form H2O
ETC does not generate ATP; purpose is to break release of energy into smaller manageable amounts

25. Chemiosmosis
Chemiosmosis: energy-coupling mechanisms that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work
In cellular respiration, H+ gradient is established by the electron transport chain, at certain steps along the ETC electron transfer causes H+ to be moved from the inside of the mitochondrial matrix to the inner membrane space; creates a proton H+ gradient

26. ATP Synthase
In addition to the proteins that make up the ETC there are also protein complexes called ATP synthases
ATP synthase: enzyme that makes ATP from ADP and inorganic phosphate; uses energy from the hydrogen gradient created by the electron transport chain
The exergonic flow of H+ ions through ATP synthase drives phosphorylation of ATP
This is an example of chemiosmosis, the use of energy in a H+ gradient to drive work (in this case ATP synthesis)
The energy stored in the proton gradient couples with the redox rxn of the ETC to make ATP (oxidative phosphorylation)
The H+ gradient is a proton-motive force

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

28. Energy Flow through Cellular Respiration: A Summary
Glucose  NADH  electron transport chain  proton-motive force  ATP
Maximum per glucose:
About
36 or 38 ATP
+ 2 ATP
+ about 32 or 34 ATP
Oxidative
phosphorylation:
electron transport
chemiosmosis
Citric
Acid
Cycle 2
Acetyl
CoA
Glycolysis
Glucose
Pyruvate
2 NADH
6 NADH
2 FADH2
CYTOSOL
Electron shuttles
span membrane or
MITOCHONDRION
ATP yield per glucose molecule oxidized is not an exact number; but it is between ATP molecules/ glucose molecule depending on efficiency of cellular respiration
4 ATP by substrate- level phosphorylation
32-34 ATP by oxidative phospohyalation

29. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen
Without the electronegative oxygen to pull electrons down the transport chain, oxidative phosphorylation stops
Two general mechanisms can oxidize organic fuel and generate ATP w/o O2: anaerobic respiration and fermentation

30. Anaerobic Respiration
Other less electronegative substances can be used in place of O2 as the final electron acceptor in an electron transport chain
EX: “sulfate-reducing” marine bacteria use sulfate ion (SO42-) at the end of their ETC; rather than H2O being the end product H2S is the by product.

31. Fermentation
A way of harvesting chemical energy without oxygen or any ETC
Recall ATP is created in glycolysis
Glucose + 2 ATP (activation energy) pyruvate (Krebs cycle) + ATP (substrate-level) + 2NADH (carries electrons to ETC) + 2 H+ +2H2O
In the case of fermentation the Krebs cycle and ETC do not exist…for the organisms to continue fermentation there must be a way to recycle NADH back to NAD+
Organisms has developed two ways to do this: alcohol fermentation and lactic acid fermentation

32. Two Types of Fermentation
Alcoholic Fermentation:
Pyruvate is converted to ethanol in two steps
Releases carbon dioxide from the pyruvate  produces acetaldehyde
Acetaldehyde is reduced by NADH to ethanol (this step generates the supply of NAD+ needed for the continuation of glycolysis
Lactic Acid Fermentation:
Pyruvate is reduced directly by NADH to form lactate as an end product, with no release of CO2
Human muscle cells make ATP by lactic acid fermentiaotn with oxygen is scarce

33. Photosynthesis as a Redox Process
During cellular respiration, energy is released from sugar when electrons associated with hydrogen are transported by carriers to oxygen, forming water as a by-product. Electrons lose potential energy as they “fall” down the electron transport chain toward electronegative oxygen, and the mitochondrion harness that energy to synthesize ATP
Photosynthesis reverses the direction of electron flow: water is split, and electrons are transferred along with hydrogen ions from the water to carbon dioxide, reducing it to sugar
Because the electrons increase in potential energy as they move from water to sugar, this process requires energy (endergonic)…the energy is provided by light

34. Photosynthesis Preview
The equation of photosynthesis is relatively simply…but the reality is the actual process is not simple…actually two main steps with multiple steps within each
Light Reaction
Photo part of the reaction; takes place in the thylakoid
Light energy is absorbed and converted into a chemical form (ATP and NADPH)
Dark Reaction
Synthesis part of the reaction; takes place in the stroma
Chemical energy from the light reaction is used to to make sugar

35. More details of the Light Reaction
Water is split  provides electrons and protons  O2 is given off as a by-product
Light absorbed by chlorophyll drives a transfer of the electrons and hydrogen ions to an electron acceptor (in photosythesis the electron acceptor is NADP+ (nicotinamide adenine dinucleotide phosphate)
Light reaction reduces NADP+ to NADPH by adding a pair of electrons along with an H+
Light reaction also generates ATP using chemiosmosis to power the addition of a phosphate group to ADP  this process is called photophosphorylation

36. More details of the Calvin Cycle
Cycle begins with incorporating CO2 from the air into organic molecules already present in the chloroplast; this process is called carbon fixation
Calvin cycle then reduces the fixed carbon to carbohydrates by adding electrons; the reducing power is provided by NADPH (from the light reaction)
To convert CO2 to C6H12O6 the Calvin cycle requires chemical energy in the form of ATP (from the light reaction)

37. i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH
Fig
H2O
CO2
Light
NADP+
ADP + P i
Calvin
Cycle
Light
Reactions
ATP
Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
NADPH
Chloroplast
[CH2O]
(sugar) O2

38. Light Reaction EVEN MORE DETAILS
(a) Excitation of isolated chlorophyll molecule
Heat
Excited
state
Photon
Ground
(fluorescence)
Energy of electron e–
Chlorophyll
molecule
Chlorophyll is a pigment located inside photosystems
Photosystems are proteins embedded in the thylakoid’s membrane
There are two photosystems associated with photosynthesis: Photosystem I and Photosystem II
When chlorophyll inside Photosystem II absorbs light it is excited due to one of its electrons being elevated to an orbital where it has more potential energy

39. (INTERIOR OF THYLAKOID)
Photosystem II
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
STROMA e–
Pigment
molecules
Photon
Transfer
of energy
Special pair of
chlorophyll a
Thylakoid membrane
Photosystem
Primary
electron
acceptor
Reaction-center
complex
Light-harvesting
complexes
Photosystem consists of a reaction-center complex and light- harvesting complexes
Light-harvesting complexes funnel the energy of light to the reaction center
A primary electron acceptor in the reaction center accepts an excited electron from chlorophyll
Enzyme splits water into two electrons, two hydrogen ions and an oxygen molecules (O2) is released and electrons are dumped into the electron transport chain between PSII and PSI

40. + H+ Electron transport chain
CO2
NADP+
reductase
Photosystem II
H2O O2
ATP Pc
Cytochrome
complex
Primary
acceptor
Photosystem I
+ H+ Fd
NADPH
Electron transport
chain Pq

41. Photosystem I
The exergonic fall of electrons to a lower energy level provides energy for the synthesis of ATP
As the electrons pass through certain parts of the electron transport chain, protons are pumpped across the membrane
The proton gradient created is used in chemiosmosis to generate ATP via ATP synthase
At the same time PSI absorbs light energy in the light-harvesting complex and transfers it to the PSI reaction-center complex, the energy travels down a second electron transport chain and is stored in NADPH
ATP and NADPH can not be used in the Calvin cycle to reduce CO2 into glucose

42. Summary of the complex light reaction
Mill
makes
ATP e–
NADPH
Photon
Photosystem II
Photosystem I
Light is absorbed by chylorphyll, with the help of photosystems I and II, the light energy travels down two electron transport chains, the first electron transport chain generates ATP, the second electron transport chain generates NADPH
Both NADPH and ATP are ready to help the Calvin cycle

43. H+ Diffusion Electron transport chain ADP + P
Fig
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE H+
Diffusion
Intermembrane
space
Thylakoid
space
Electron
transport
chain
Inner
membrane
Thylakoid
membrane
Figure Comparison of chemiosmosis in mitochondria and chloroplasts
ATP
synthase
Matrix
Stroma
Key
ADP + P i
ATP
Higher [H+] H+
Lower [H+]

44. Fig. 10-17 STROMA (low H+ concentration) Cytochrome complex
Photosystem II
Photosystem I
4 H+
Light
NADP+
reductase
Light Fd 3
NADP+ + H+ Pq
NADPH e– Pc e– 2
H2O 1
1/2 O2
THYLAKOID SPACE
(high H+ concentration)
+2 H+
4 H+ To
Calvin
Cycle
Figure The light reactions and chemiosmosis: the organization of the thylakoid membrane
Thylakoid
membrane
ATP
synthase
STROMA
(low H+ concentration)
ADP +
ATP P i H+

46. Dark Reaction: EVEN MORE DETAILS
Calvin cycle is anabolic, building carbohydrate from smaller molecules and consuming energy
Carbon enters the Calvin cycle in the for of CO2 and leaves as sugar
The cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high-energy electrons to make the sugar
Calvin cycle is broken into three phases:
Phase 1: Carbon fixation
Phase 2: Reduction
Phase 3: Regeneration of the Co2 acceptor (RuBP)

47. Figure 10.18 The Calvin cycle
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco 3 P P
Short-lived
intermediate 3 P P 6 P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate 6
ATP
6 ADP
3 ADP
Calvin
Cycle 6 3 P P
ATP
1,3-Bisphosphoglycerate 6
NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+ 6 P i
Figure The Calvin cycle 5 P
G3P 6 P
Glyceraldehyde-3-phosphate
(G3P)
Phase 2:
Reduction 1 P
Glucose and
other organic
compounds
Output
G3P
(a sugar)

48. Electron transport chain
Fig
H2O
CO2
Light
NADP+
ADP + P i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
RuBP
3-Phosphoglycerate
Calvin
Cycle
ATP
G3P
Figure A review of photosynthesis
Starch
(storage)
NADPH
Chloroplast O2
Sucrose (export)