Photosynthesis Flashcards
What sort of ion does a chlorophyll molecule contain?
Mg2+
What sort of head and tail do chlorophyll molecules have?
Form a tetrapyrrole ring.
Phytyl tail
What part of the chlorophyll molecule is responsible for light absorption?
Conjugated π- electron system in the tetrapyrrole ring
Which biomolecule has the highest redox potential?
P680+ special pair
+1200mv redox potential
How do antenna complexes capture and concentrate light energy?
Use pigments non-covalently bound to antenna proteins. Increase excitation rate by 2 orders of magnitude
What is the main residue on P680+ with a positive redox potential?
Tyrosine
Which path do special pair electrons take up PSII?
Water in manganese cluster -> Special pair -> chlorophyll aA -> pheophytin A -> Plastoquinone QA -> Plastoquinone QB
How many electrons does it take for PQ to reduce to PQH2
2
Why are photosystem reaction centres horseshoe shaped?
Keep charges from meeting and creating heat.
How many plastoquinols are required to create O2
2
Where is plastoquinone reduced to plastoquinol?
Thylakoid lumen of chloroplasts
What is the path of the electron in PSI?
Plastocyanin (+370mV) -> P700 -> Chlorophyll a1 -> Chlorophyll a2 -> Phylloquinone -> ferrodoxin
What ion does plastocyanin have in its active site?
copper ion
What residues coordinate the ion in the plastocyanin active site?
2 His, 1 Cys and 1 Met
What binds to the ferrodoxin active site?
2Fe-2S, bound by several cysteines
What does marcus theory state?
At first, reaction rate increases with feasibility, then as -ΔG gets large, reaction rate slows. This is due to reorganisation energy accommodating the difference in charge
What is cytochrome b6f comparable to in the mitochondria?
complex III
How many haems is cytochrome b6f bound to?
4
How are C and B type haems bound to cytochrome b6f respectively?
C haems are covalently bonded to protein
B haems are linked to Fe ions via coordination bonds
When PQH2 is oxidised, where are the two protons deposited?
Lumen
In jablonski diagrams how can photons be re-emitted from ground state
Fluorescence
What energy gap do blue photons match in jablonski diagrams?
S0 -> S2
Why are internal conversions slower between S1 and S0 than S2 and S1
The electron is closer to the nucleus in the S1 to S0 state so there is lower energy
Which way can be quicker than internal conversions from S1 to ground state?
Fluorescence (10^-9s)
How does energy differ between reaction centre and the rest of the antenna?
Lower energy in the reaction centre as energy cascades down to the reaction centre by FRET
When does FRET take place?
Occurs when two chlorophylls are in close proximity and have overlapping excited state energy levels
What is FRET transfer time inversely proportional to?
6th power of the distance. only efficient under 7nm
Why is photosynthesis not 100% efficient?
Reflection
Photochemical inefficiency
Missed photons
What does proton motor force couple?
Electron transfer to proton transfer across the membrane
What does the a-subunit in ATP synthase do?
Connects each side of the membrane to the c-subunit glutamate residues
What do 8-15C subunits in ATP synthase do?
acts as a rotor
What do b2 and δ-subunits do in ATP synthase?
Form the stator bridge between the F1 and F0 domains to keep them coupled
What does the γ-subunit of ATP synthase do?
Trasmits torque from F0 to F1, changing the conformation of the β-subunits between O, L and T
How does the a subunit spin the c subunit in ATP synthase?
The a subunit contains an arginine residue which affects the pKa of the glutamate residue on the c subunits. The arginine deprotinates the c-ring, allowing it to rotate. Glutamate is reprotinated on the c-ring.
What conformation is ATP formed on the β subunits of ATP synthase?
Tight state
How does c-ring size affect the pmf multiplier?
The larger the c-ring size, the larger the pmf multiplier
Why is ~50% total leaf protein rubisco?
High rubisco concentrations are needed to match ATP and NADPH supply in the calvin cycle
When CO2 combines with RuBP, what forms?
An unstable 6 carbon intermediate which splits into two 3-phosphglycerate molecules
In the conversion of 1,3-biphosphoglycerate to glyceraldhye-3-phosphate, what happens?
Glyceraldehyde-3-phosphate dehydrogenase recruits NADPH to reduce GAP. The acyl group is converted to an aldehyde group.
How is RuBP regenerated?
A series of complex reactions, the last being ribulose 5-phosphate being phosphorylated with ATP by phosphoribulose kinase
What does thioredoxin do?
Detects changes in the redox state of the stroma caused by ferrodoxin reduction.
Regulates fructose 1,6- bisphophate, GAP dehydrogenase and phosphoribulokinase
How does rubisco bind to CO2?
Active site contains lysine which reacts with CO2 to form a carbamate ion. This binds to Mg2+ and recruits RuBP to react with CO2
What sort of photons are absorbed by chlorophyll?
Only absorb photons with energy equal to the gap between electron orbitals
