1. Lecture #1
Photosynthesis
Creating sugars
Chapter 10

2. Overview of Photosynthesis
Anabolic Pathway
6CO2 + 6H2O + Light --> C6H12O6 + 6O2
Only those organisms with chloroplast can produce sugars
Examples: plants, photosynthetic bacteria, etc.

3. Redox reactions Redox reactions Oxidation-reduction
OIL RIG (adding e- reduces + charge)
Oxidation is e- loss; reduction is e- gain
Reducing agent: e- donor
Oxidizing agent: e- acceptor

4. Photosynthesis in nature
Autotrophs:
biotic producers; photoautotrophs; chemoautotrophs; obtains organic food without eating other organisms
Heterotrophs:
biotic consumers; obtains organic food by eating other organisms or their by-products (includes decomposers)

5. The chloroplast Sites of photosynthesis Pigment: chlorophyll
Plant cell: mesophyll
Gas exchange: stomata
Double membrane
Thylakoids: membranes in which LDR occur
Grana: Stacks of thylakoid
Stroma: Space where LIR occur

6. Light Travels in waves Speed of light = frequency x wavelength
Wavelengths for visible light range between about 375nm and 760nm
Lower wavelength = violet light
Higher wavelegth = red light

7. Chlorophyll Two types of chlorophyll
Chlorophyll a: Absorbs best at about 420nm and 670nm (violet and red respectively)
Chlorophyll b: 440nm and 630nm
Cartenoids: 420nm to 590nm; appear yellow-orange
No chlorophyll absorbs green wavelengths – they are reflected giving plants their color.

8. Photosynthesis: An overview
Redox process
H2O is split, e- (along w/ H+) are transferred to CO2, reducing it to sugar
2 major steps:
light reactions (“photo”)
NADP+ (electron acceptor) to NADPH
Photophosphorylation
ADP ---> ATP
Calvin cycle (“synthesis”)
Carbon fixation: carbon into organics

9. Photosystems Light harvesting units of the thylakoid membrane
Composed mainly of protein and pigment antenna complexes
Antenna pigment molecules are struck by photons
Energy is passed to reaction centers (redox location)
Excited e- from chlorophyll is trapped by a primary e- acceptor

10. Noncyclic electron flow
Photosystem II (P680):
photons excite chlorophyll e- to an acceptor
e- are replaced by splitting of H2O (release of O2)
e-’s travel to Photosystem I down an electron transport chain
(Pq ~ cytochromes ~ Pc)
as e- fall, ADP ---> ATP
noncyclic photophosphorylation

11. Noncyclic electron flow
Photosystem I (P700):
‘fallen’ e- replace excited e- to primary e- acceptor
2nd ETC
( Fd ~ NADP+ reductase)
transfers e- to NADP+ ---> NADPH
...to Calvin cycle…
These photosystems produce equal amounts of ATP and NADPH

12. The Calvin cycle
3 molecules of CO2 are ‘fixed’ into glyceraldehyde 3-phosphate (G3P)
Phases:
1- Carbon fixation: each CO2 is attached to RuBP (rubisco enzyme)
2- Reduction: electrons from NADPH reduces to G3P; ATP used up
3- Regeneration: G3P rearranged to RuBP; ATP used; cycle continues

13. Calvin Cycle, net synthesis
For each G3P (and for 3 CO2)…….
Consumption of 9 ATP’s & 6 NADPH
light reactions regenerate these molecules; used ADP and NADP+ return to thylakoid membranes
G3P can then be used by the plant to make glucose and other organic compounds

14. Cyclic electron flow Alternative cycle when ATP is deficient
Photosystem I used but not II; produces ATP but no NADPH
Why? The Calvin cycle consumes more ATP than NADPH…….
Cyclic photophosphorylation

15. Alternative carbon fixation methods
Photorespiration: hot/dry days; stomata close; CO2 decrease, O2 increase in leaves; O2 added to rubisco; no ATP or food generated
How can plants overcome these problems?
Two solutions: Depends on the climate the plant is located in
C4 Plants
CAM Plants

16. Two Solutions…
1- C4 plants: 2 photosynthetic cells, bundle-sheath & mesophyll; PEP carboxylase (instead of rubisco) fixes CO2 in mesophyll; new 4C molecule releases CO2 (grasses)

17. Carbon Fixation
2- CAM plants: open stomata during night, close during day (crassulacean acid metabolism); cacti, pineapples, etc.

18. A review of photosynthesis

19. Lecture #2
Cellular Respiration
Harvesting Chemical Energy
Chapter 9

20. Principles of Energy Harvest
Catabolic pathway
Fermentation (Anaerobic)
Cellular Respiration (Aerobic)
C6H12O6 + 6O2 ---> 6CO2 + 6H2O + Energy (ATP + heat)

21. Redox reactions Oxidation-reduction
OIL RIG (adding e- reduces + charge)
Oxidation is e- loss; reduction is e- gain
Reducing agent: e- donor
Oxidizing agent: e- acceptor

22. Oxidizing agent in respiration
NAD+ (nicotinamide adenine dinucleotide)
Removes electrons from food (series of reactions)
NAD+ is reduced to NADH with the addition of an e-
Enzyme action: dehydrogenase
Oxygen is the eventual e- acceptor

23. Electron transport chains
Electron carrier molecules (membrane proteins)
Shuttles electrons that release energy used to make ATP
Sequence of reactions that prevents energy release in 1 explosive step
Electron route:
Food --> NADH --> electron transport chain --> oxygen

24. Cellular respiration Glycolysis: degrades glucose into pyruvate
Kreb’s Cycle: pyruvate into carbon dioxide
Electron Transport Chain: electrons passed to oxygen

25. Glycolysis
1 Glucose  2 pyruvate molecules
Energy investment phase: cell uses ATP to phosphorylate fuel
Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation

26. Glycolysis Net energy yield per glucose molecule:
2 ATP plus 2 NADH
No CO2 is released
Occurs anaerobically
First step in any respiratory process
Occurs in the cytosol of the cell

27. Fermentation Two types: Alcoholic and Lactic Acid Anaerobic process
In cytosol of the cell
Produces an additional 2 ATP and either Ethyl Alcohol or Lactic Acid
Organisms vary: Humans – Lactic, Bacteria/Yeast - Alcoholic

28. Alcoholic Fermentation
Bacteria/Yeast
Produces Ethyl Alcohol: compound found in all alcoholic beverages
2 Pyruvic Acid  2 ATP + C2H5OH + CO2
Overall production, including glycolysis yields 4 ATP, 2 NADH, Ethyl alcohol and Carbon Dioxide

29. Lactic Acid Fermentation
2 Pyruvic Acid  2 ATP + CH3CH(OH)COOH
Substrate level phosphorylation
Regenerates NAD+ by using the electrons transferred from glycolysis
Human muscle cells make Lactic Acid when sugar catabolism outpaces the muscle’s supply of oxygen from the blood

30. Kreb’s Cycle If molecular oxygen is present…….
Each pyruvate is converted into acetyl CoA (begin w/ 2):
CO2 is released;
NAD+ ---> NADH;
coenzyme A (from B vitamin), makes molecule very reactive

31. Kreb’s Cycle
From this point, each turn 2 C atoms enter (pyruvate) and 2 exit (carbon dioxide)
Oxaloacetate is regenerated (the “cycle”)
For each pyruvate that enters:
3 NAD+ reduced to NADH,
1 FAD+ reduced to FADH2 (riboflavin, B vitamin);
1 ATP molecule (GTP)

32. Electron transport chain
Occurs on the inner (folded) Mitochondria membrane
Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen
NADH and FADH2 come from the Kreb cycle
Each NADH = 3 ATP
Each FADH2 = 2 ATP

33. Electron transport chain
ATP synthase: produces ATP by using the H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain;
This enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)
Chemiosmosis: energy coupling mechanism

34. Review: Cellular Respiration
Glycolysis: ATP (substrate-level phosphorylation)
Kreb’s Cycle: ATP (substrate-level phosphorylation)
Electron transport & oxidative phosphorylation: NADH (glycolysis) = 6ATP NADH (acetyl CoA) = 6ATP NADH (Kreb’s) = 18 ATP
2 FADH2 (Kreb’s) = 4 ATP
38 TOTAL ATP/glucose

35. Related metabolic processes
Fermentation:
alcohol ~ pyruvate to ethanol
lactic acid ~ pyruvate to lactate
Facultative anaerobes (yeast/bacteria)
Beta-oxidation lipid catabolism