Photosynthesis

Question 1

What sort of ion does a chlorophyll molecule contain?

Answer 1

Mg2+

Question 2

What sort of head and tail do chlorophyll molecules have?

Answer 2

Form a tetrapyrrole ring.
Phytyl tail

Question 3

What part of the chlorophyll molecule is responsible for light absorption?

Answer 3

Conjugated π- electron system in the tetrapyrrole ring

Question 4

Which biomolecule has the highest redox potential?

Answer 4

P680+ special pair
+1200mv redox potential

Question 5

How do antenna complexes capture and concentrate light energy?

Answer 5

Use pigments non-covalently bound to antenna proteins. Increase excitation rate by 2 orders of magnitude

Question 6

What is the main residue on P680+ with a positive redox potential?

Answer 6

Tyrosine

Question 7

Which path do special pair electrons take up PSII?

Answer 7

Water in manganese cluster -> Special pair -> chlorophyll aA -> pheophytin A -> Plastoquinone QA -> Plastoquinone QB

Question 8

How many electrons does it take for PQ to reduce to PQH2

Answer 8

2

Question 9

Why are photosystem reaction centres horseshoe shaped?

Answer 9

Keep charges from meeting and creating heat.

Question 10

How many plastoquinols are required to create O2

Answer 10

2

Question 11

Where is plastoquinone reduced to plastoquinol?

Answer 11

Thylakoid lumen of chloroplasts

Question 12

What is the path of the electron in PSI?

Answer 12

Plastocyanin (+370mV) -> P700 -> Chlorophyll a1 -> Chlorophyll a2 -> Phylloquinone -> ferrodoxin

Question 13

What ion does plastocyanin have in its active site?

Answer 13

copper ion

Question 14

What residues coordinate the ion in the plastocyanin active site?

Answer 14

2 His, 1 Cys and 1 Met

Question 15

What binds to the ferrodoxin active site?

Answer 15

2Fe-2S, bound by several cysteines

Question 16

What does marcus theory state?

Answer 16

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

Question 17

What is cytochrome b6f comparable to in the mitochondria?

Answer 17

complex III

Question 18

How many haems is cytochrome b6f bound to?

Answer 18

4

Question 19

How are C and B type haems bound to cytochrome b6f respectively?

Answer 19

C haems are covalently bonded to protein
B haems are linked to Fe ions via coordination bonds

Question 20

When PQH2 is oxidised, where are the two protons deposited?

Answer 20

Lumen

Question 21

In jablonski diagrams how can photons be re-emitted from ground state

Answer 21

Fluorescence

Question 22

What energy gap do blue photons match in jablonski diagrams?

Answer 22

S0 -> S2

Question 23

Why are internal conversions slower between S1 and S0 than S2 and S1

Answer 23

The electron is closer to the nucleus in the S1 to S0 state so there is lower energy

Question 24

Which way can be quicker than internal conversions from S1 to ground state?

Answer 24

Fluorescence (10^-9s)

Question 25

How does energy differ between reaction centre and the rest of the antenna?

Answer 25

Lower energy in the reaction centre as energy cascades down to the reaction centre by FRET

Question 26

When does FRET take place?

Answer 26

Occurs when two chlorophylls are in close proximity and have overlapping excited state energy levels

Question 27

What is FRET transfer time inversely proportional to?

Answer 27

6th power of the distance. only efficient under 7nm

Question 28

Why is photosynthesis not 100% efficient?

Answer 28

Reflection
Photochemical inefficiency
Missed photons

Question 29

What does proton motor force couple?

Answer 29

Electron transfer to proton transfer across the membrane

Question 30

What does the a-subunit in ATP synthase do?

Answer 30

Connects each side of the membrane to the c-subunit glutamate residues

Question 31

What do 8-15C subunits in ATP synthase do?

Answer 31

acts as a rotor

Question 32

What do b2 and δ-subunits do in ATP synthase?

Answer 32

Form the stator bridge between the F1 and F0 domains to keep them coupled

Question 33

What does the γ-subunit of ATP synthase do?

Answer 33

Trasmits torque from F0 to F1, changing the conformation of the β-subunits between O, L and T

Question 34

How does the a subunit spin the c subunit in ATP synthase?

Answer 34

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.

Question 35

What conformation is ATP formed on the β subunits of ATP synthase?

Answer 35

Tight state

Question 36

How does c-ring size affect the pmf multiplier?

Answer 36

The larger the c-ring size, the larger the pmf multiplier

Question 37

Why is ~50% total leaf protein rubisco?

Answer 37

High rubisco concentrations are needed to match ATP and NADPH supply in the calvin cycle

Question 38

When CO2 combines with RuBP, what forms?

Answer 38

An unstable 6 carbon intermediate which splits into two 3-phosphglycerate molecules

Question 39

In the conversion of 1,3-biphosphoglycerate to glyceraldhye-3-phosphate, what happens?

Answer 39

Glyceraldehyde-3-phosphate dehydrogenase recruits NADPH to reduce GAP. The acyl group is converted to an aldehyde group.

Question 40

How is RuBP regenerated?

Answer 40

A series of complex reactions, the last being ribulose 5-phosphate being phosphorylated with ATP by phosphoribulose kinase

Question 41

What does thioredoxin do?

Answer 41

Detects changes in the redox state of the stroma caused by ferrodoxin reduction.
Regulates fructose 1,6- bisphophate, GAP dehydrogenase and phosphoribulokinase

Question 42

How does rubisco bind to CO2?

Answer 42

Active site contains lysine which reacts with CO2 to form a carbamate ion. This binds to Mg2+ and recruits RuBP to react with CO2

Question 43

What sort of photons are absorbed by chlorophyll?

Answer 43

Only absorb photons with energy equal to the gap between electron orbitals