What is the Photosynthesis reaction?
6 CO2 + 6 H2O –(light energy)–>C6H12O6 (glucose) + 6O2
What is highly evolved to maximize the efficiency of photosynthesis?
The structure of leaves and chloroplasts
What allows for the gas exchange in photosynthesis?
Between the atmosphere and inside the leaf
*The air spaces in leaves
What maximizes membrane surface area in photosynthesis?
Thylakoid membranes
Stomata
Through which O2 & CO2 are exchanged with the atmosphere
Thylakoids
- Light absorption by chlorophylls & carotenoids
- electron transport
- STP synthesis by ATP synthase
What type of process is photosynthesis?
It is a redox process
- Electrons are taken from one reactant and moved to another
In the photosynthesis reaction, what is the reduction agent? Oxydation agent?
Reduction (lose e) = 6 CO2
Oxidation (gain e) = 12 H2O
What are the two parts to photosynthesis? What do they do?
1) The light reactions: Collect light energy, Oxidize H20, and stores energy as ATP and NADPH
2) Carbon fixation (Calvin cycle): Use ATP and NADPH to reduce CO2
Light reactions (4 things)
1) H2O enters chloroplast, and collects energy from sunlight
2) The light reaction has ADP + Pi and NADP+ that come in
3) It makes ATP and NADPH
4) O2 leaves the chloroplasts
Calvin Cycle (Carbon Fixation) 4 things
1) CO2 enters chloroplast
2) The Calvin cycle has ATP and NADPH that come in
3) It makes ADP + Pi and NADP+
4) Sugars (carbohydrates) leave the chloroplasts
Stroma
The space around the thylakoids
- The calvin cycle
Light:
What type and color are the shortest, most energetic wavelengths?
Gamma rays
Purple/ Blue
Light:
What type and color are the longest, lowest enegy wavelengths?
Radio waves
Red
Why are plants green?
The color green is due to the chlorophyll absorbing red, blue, etc light… and reflecting and transmitting green light
What are the main pigments absorbing light for photosynthesis? are they polar or nonpolar?
Chlorophylls and Carotenoids are the main pigments absorbing light for photosynthesis
They are quite nonpolar
What is always bound to proteins?
Chlorophyll
Which is only present in the Thylakoid membrane? Chlorophylls and Carotenoids?
Chlorophylls
What does the hydrophobic tail allow the chlorophyll to do?
Its hydrophobic tail allows it to interact with proteins in the thylakoid membrane
What did Joseph Priestly discover in 1772?
- He discovered Oxygen
- Found that plants could purify air
What did Jan Ingen-Housz discover in 1781?
- He discovered that only green plants could purify the air but they have to be in the light
What did Julius Mayer discover in 1845?
- He discovered that energy from the sun is converted by photosynthesis into a chemical form
- Found that plants are only green when they grown in the light
What do Aerotactic bacteria move towards?
They move towards the oxygen
Theodor Engelmann 1883:
What wavelengths of light are the most important for photosynthesis?
Chlorophyll is best produce in Red & Blue waves
- which closely matches the absorption spectrum of leaf pigments
What type of light is always at a longer wavelength?
Light give off as Fluorescence is always at a longer wavelength, and some energy is lost in the transfer process
- 2nd law of thermodynamics
Explain what happens in the first two parts of a light reaction
1) A photon passes through the Photosystem II
- 2 H2O comes in, and produces 4 H+ + O2
- passes 4e- through the Photosystem II to the electron transport chain
* Oxidizes H20 and taking its electrons*
2) The electrons pass through the Cytochrome complex, and through the Plastocyanin transporter protein
Explain what happens in the middle of a light reaction
3) A photon of light passes through the Photosystem I
- The electrons from the Plastocyanin transporter protein also pass through the Photosystem I
4) The electrons then pass through the Ferredoxin transporter protein
5) Then in NADP+ reductase:
- 2H+ + NADP+ come in, and produces NADPH
Explain what is the last steps of the light reaction
6) The ATP made through the ATP Synthase combine with the NADPH made by the NADP+ reductase which form the Calvin cycle
What does the light-harvesting system do?
It helps the reaction centre by absorbing lots and lots of light energy
The Electron Transport Chain-Pt I (Photosystem II)
__ photons of light will transfer __ electrons from ____ molecules to give __ and ______
4 photons of light will transfer 4 electrons from 2 H2O molecules to give O2 and 4 electrons (e-)
The Electron Transport Chain-Pt I (Photosystem II)
The __ are moved to the next complex using ___ (__________)
This also moves ____ across the membrane into the ____________
The e- are moved to the next complex using PQ (a mobile e- carrier).
This also moves H+ ions across the membrane into the Thylakoid Lumen
The Electron Transport Chain-Pt II (Cytochrome Complex)
- _____ the mobile e- carrier passes its e- to the next ____________
- The e- continues through the _______________ and H+ ions are actively transported into the ___________, building up the proton motive force
- PQH2 the mobile e- carrier passes its e- to the next protein complex
- The e- continues through the electron transport chain and H+ ions are actively transported into the Thylakoid Lumen, building up the proton motive force
The Electron Transport Chain-Pt III (Photosystem I)
When the e- reaches ___________ it has very little energy left. ____ and its __________, absorb light energy and re-excite the ___
When the e- reaches Photosystem I it has very little energy left. PSI and its light harvesting complex, absorb light energy and re-excite the e-
The Electron Transport Chain-Pt III (Photosystem I)
- The re-excited e- is then used to make ____ by the _____ _______ ______
- The cell now has a mobile source of high energy electrons that can be used to convert _____ into ________
- The re-excited e- is then used to make NADPH by the NADP reductase enzyme
- The cell now has a mobile source of high energy electrons that can be used to convert CO2 into carbohydrates
Which photosystem excites the electrons and makes NADPH? Which one uses oxygen?
Photosystem I
Photosystem II
The loss of energy is coupled to what?
The loss of energy is coupled to the movement of H+ ions
After the 3 parts of the electron transport chain, what happens?
Chemiosmosis
The build up of H+ ions in the thylakoid lumen can now be used by an ATP synthase to convert ADP to ATP
- It works just like in Mitochondria but here it is called Photophosphorylation
_____ uses light energy to oxidize ____ creating __, it then passes the electrons to the ______________
PSII uses light energy to oxidize H2O creating O2, it then passes the electrons to the electron transport chain
The _____ moves electrons, _____ energy, while pumping H+ ions into the ___________
The ETC moves electrons, losing energy, while pumping H+ ions into the thyakoid lumen (generating a pmf)
____then re-excites the electrons giving them enough energy to reduce ______ into _______
PSI then re-excites the electrons giving them enough energy to reduce NADP+ into NADPH
The ________ uses the potential energy of the ___ to generate _____
The ATP synthase uses the potential energy of the pmf to generate ATP
At the end, the cell has ______ (_____ energy electrons) and ______ to use for making __________
At the end, the cell has NADPH (high energy electrons) and ATP to use for making carbohydrates
Light Reactions occur in the _____________
Dark Reactions occur in the ________________
Light Reactions occur in the Thylakoid Membrane
Dark Reactions occur in the Stroma of the chloroplast
How can we test where the atoms go in photosynthesis?
Using RadioIsotopes such as (18) oxygen
Radioisotopes are generally atoms with _________.
This makes the atom ______________________?
Radioisotopes are generally atoms with extra neutrons.
This makes the atom unstable and it tends to decay or breakdown giving off particles, then we can detect these particles and thus the presence of Radioisotopes
What is (18)O ?
It is a stable isotope because it does not breakdown
(18) O composes ____ of natural O, but can be enriched to higher levels
0.2%
How could we see if the O2 produced by photosynthesis comes from CO2? What is the result
If we would feed some C(18)O2 to a plant, shine light on the plant, then analyze the O2 produced
- We would see that it doesnt contain radioactive oxygen
How can we be sure that the O2 produced by photosynthesis does not come from CO2?
By performing a 2nd experiment, the reverse
- Water the plant with H2 (18)O then analyze the O2 produced
- We would see the radioactive oxygen produced by the plant
What would these experiments tell us? (4 things)
1) C of CO2 ends up in carbohydrate
2) H+ from H2O broken by PSII makes ATP
3) O2 released from H2O by PSII
4) H2O from Dehydration reactions in the Calvin cycle
____ diffuses into the _____ of the chloroplast where enzymes use it to make __________
CO2 diffuses into the stroma of the chloroplast where enzymes use it to make carbohydrates
Carbon Fixation Reactions (Calvin cycle):
_____ from the atmosphere is reduced and energized using _____ and _____ to give simple __________
CO2 from the atmosphere is reduced and energized using NADPH and ATP to give simple carbohydrates (Triose Phosphate)
What was the goal of the research team performing the Calvin’s experimental set up? What was the experiment
To identify thec arbon compounds produced by photosynthesis
- They grew green algae, fed them (14)CO2 (-radioactive) , and rapidly killed the cells
= which caused the enzymes to stop working
Steps of the Chlorella experiment
1) Cells were rapidly killed in hot ethanol and carbohydrates were extracted
2) Carbohydrates were separated by chromatography (wet then dry)
3) The chromatography sheet exposed to x-ray film to detect the (14)C = autoradiography
4) Radioactive spots could then be identified by comparison to know chemicals
What is the first product of Carbon fixation?
3-phosphglycerate
What are the 3 phases of the Calvin Cycle?
1) Carbon fixation =6 CO2 is incorporated into an organic molecule via rubisco
2) Reduction and carbohydrate production = 12 ATP are used as a source of energy, and 12 NADPH donates high energy electrons
3) Two G3P are used to make Glucose and sugars
4) Regeneration of RuBP= 10 G3P are needed to regenerate 6RuBP via several enzymes. ATP is required for RuBP regeneration
* *RuBP= 6 Ribulose bisphosphate**
What is the most abundant enzyme on earth?
Ribulose 1,5-bisphosphate carboxylase/oxygenase
- It accounts for about 40% of leaf soluble protein in all plants
- It fixes CO2
CO2 is fixed by _______
Rubisco
The initial product of Rubisco, _________________, is reduced using the electrons from _______ and energy from _____
The initial product of Rubisco, 3-Phosphoglycerate, is reduced using the electrons from NADPH and energy from ATP
A ______(simple carbohydrate) is produced and then the Calvin Cycle regenerates the starting compound _______________
A triose phosphate(simple carbohydrate) is produced and then the Calvin Cycle regenerates the starting compound (Ribulose-1,5-bisphosphate)
The use of ____ and ______ during carbon fixation, regenerates ___ and____ for the light reactions
The use of ATP and NADPH during carbon fixation, regenerates ADP and NADP+ for the light reactions
What are the 3 main phases of the Calvin cycle?
1) Carbon fixation
2) Reduction and carbohydrate production
3) Regeneration of RuBP