Lecture 10 - Carbohydrate Anabolism 1 Flashcards
What is the delta G of the photosynthesis reaction?
2868 kJ/mol
Define photosynthesis
The formation of carbohydrates from CO2 and H2O using light as an energy source
What is the photosynthesis reaction?
6 CO2 + 6 H2O -> C6H12O6 + 6 O2
What is the electron acceptor in the photosynthesis reaction?
CO2
What is the electron donor in the photosynthesis reaction for green plants and algae?
H2O
What gets reduced in the photosynthesis reaction and what does it become?
Carbon dioxide to carbohydrate
What gets oxidized in the photosynthesis reaction and what does it become (for green plants and algae)?
H2O to O2
Which 2 processes give rise to the carbon cycle?
Respiration and photosynthesis
What is the electron donor in the photosynthesis reaction for green sulfur bacteria?
H2S
What is the electron donor in the photosynthesis reaction for purple non-sulfur bacteria?
Isopropanol
What gets oxidized in the photosynthesis reaction and what does it become (for green sulfur bacteria)?
H2S to 12S
What gets oxidized in the photosynthesis reaction and what does it become (for purple non-sulfur bacteria)?
Isopropanol to acetone
What are the 2 reactions that occur during photosynthesis?
1) Electrons (on carriers) are generated from the electron donor
2) Electrons (from carrier) reduces the CO2
What is the function of hill reagents?
Shows that reduced electron carriers are produced independent of CO2 using light energy
What are some examples of hill reagents?
Fe3+, NADP+
What is the function of heavy oxygen?
Shows that the molecular oxygen used in photosynthesis was derived from H2O, not CO2
What is the difference between heavy oxygen and normal oxygen?
Heavy oxygen is an isotope of normal oxygen, with 18 electrons instead of 16
Where does photosynthesis occur in eukaryotic plants?
Chloroplast
What absorbs light energy in the chloroplast?
Pigments in the thylakoid membrane
Enzymes involved in CO2 reduction are located in _____
The stroma surrounding the thylakoid membranes
What occurs in the light stage of photosynthesis?
- Light energy is absorbed by the membrane for the production of NADPH and ATP
- Water is oxidized to O2
Where does the light stage of photosynthesis occur?
Membrane of thylakoid vesicles
What occurs in the dark stage of photosynthesis?
CO2 is reduced to carbohydrates using NADPH and ATP from the light stage
Is light required for the dark stage of photosynthesis?
No
Where does the dark stage of photosynthesis occur?
Stroma
The principal light absorbing pigment is ______
Chlorophyll
Chlorophyll and other pigments form a _____
Light harvesting complex
What does light energy have properties of?
Both a particle and a wave
What is the formula for the speed of light?
c = (lambda)(v) / wavelength * frequency
What is the relationship between energy and wavelength?
Inverse
What is the relationship between energy and frequency?
Direct
Do UV rays have a long or short wavelength and what does this mean for energy?
Short wavelength, so high energy
Chlorophyll absorbs in the ___ region of the visible spectrum and supplementary excitations can occur in the ____ region
- Red/lower energy
- Blue
Chlorophyll reflects light in the _____ region
Green
How does chlorophyll absorb light energy?
- Photon hits the aromatic rings of chlorophyll (photoexcitation)
- Pushes electrons of chlorophyll or other pigment into a higher energy state
- Electrons return back to ground state and release energy and energy is “captured” as the electrons pass to a photosystem
What is important about molecules with aromatic components that have conjugated bonds with pi-electrons?
The pi-electrons are photoexcited at lower energy levels because they are less tightly bound
_____ wavelengths produce higher energy excitation
Shorter
What does photosystem 1 consist of?
- 16 proteins
- 168 chlorophylls
- Carotenoids
- Fe-S clusters
- Phylloquinones
What is another name for photosystem 1?
P700
What is another name for photosystem 2?
P680
What do P700 and P680 do together?
Move electrons from H2O to reduce NADP+ to NADPH
What is important of a photoexcited electron?
It is less tightly bound to the molecule and can be given up more easily, therefore the molecule is a better reducing agent
What is the change in reduction potential for photosystem 2?
1.0 V -> -0.6 V
What is the change in reduction potential for photosystem 1?
0.4 V -> -1.0 V
How many times is an electron photoexcited to produce NADPH and ATP?
Twice
How is O2 produced during photosynthesis?
By the oxidation of H2O in the oxygen evolving complex
How is ATP produced during photosynthesis and what is this process called?
- Electrons flow through a photosystem, allowing protons to be pumped across a membrane to form a gradient
- Gradient is exploited by ATPase to produce 3 ATP
- Process is called photophosphorylation
Photosystem 2 is a _______ type system
Pheophytin-quinone
Photosystem 1 is a _____ type system
Ferridoxin
Does photosystem 2 contain more chlorophyll a or b?
About equal amounts
Does photosystem 1 contain more chlorophyll a or b?
A
______ carries an electron between the 2 photosystems
Plastocyanin
What are the molecules in order in the cytochrome bf-quinone complex?
Plastoquinone -> cytochrome bf -> plastocyanin
What does the oxygen evolving complex contain and what is its function?
- Contains manganese
- Pulls electrons out of water to replace the electrons that move from PS 2 -> PS 1 -> NADP+ and generates molecular oxygen