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Michaelmas Term 1 > Photosynthesis: Energy And Carbon Capture > Flashcards

Photosynthesis: Energy And Carbon Capture Flashcards

1
Q

Describe lithoautotrophs

A
  • extract electrons from reduced forms of rock unwraps
  • dependent on abundant sources of reduced mineral substrates
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2
Q

List some lithoautotrophs

A
  • hydrogen-sulphide oxidisers
  • nitrifying bacteria
  • iron-oxidisers
  • hydrogen-oxidisers
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3
Q

Where are abundant sources of reduced mineral substrates?

A

Hydrothermal vents on the seabed

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4
Q

What did the evolution do photosynthesis do?

A
  • oxygenated earth’s atmosphere
  • evolution of complex life
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5
Q

When was the Great Oxidation Event?

A

2500Mya (Precambrian)

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6
Q

How much did O2 rise during the Great Oxidation Event

A
  • from 0 PO2 to 5-18% of present levels
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7
Q

Great Oxidation Event is shown graphically by

A

Plotting Atmsophere PO2 (atm) against billions of years ago. Oxygen emerges at 2.5

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8
Q

Why is conversion of water to oxygen energetically unfavourable

A

2NADP+ + 2H2O -> 2NADPH + O2 + 2H+
ΔG >0

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9
Q

How does photosynthesis happen, if it is energetically unfavourable

A

Uses absorbed solar energy to drive the process

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10
Q

What happens to chlorophyll on light absorption?

A

excitation of an electron from ground state to high energy level

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11
Q

List the 3 ways in which excited chlorophyll can lose its energy

A
  1. Fluoresce
  2. Resonance energy transfer
  3. Electron transfers
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12
Q

Which chlorophyll type fluoresces to lose energy?

A

Isolated molecules

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13
Q

Which chlorophyll type uses resonance energy transfer to lose its high energy

A

Antenna complex

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14
Q

Which chlorophyll type uses electron transfers to get rid of its high energy state?

A

Electron transfers

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15
Q

What are photosystems?

A

Chlorophyll molecules associated with multi-subunit proteins

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16
Q

What do photosystems contain?

A
  • antenna complex
  • photochemical reaction centre
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17
Q

What does an antenna complex do?

A

Funnels excited electrons to the photochemical reaction centre through resonance energy transfer/fluorescence

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18
Q

What is the fundamental role of captured light?

A

To promote charge separation in the photochemical reaction centre

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19
Q

What is a phycobilisome (PBS) built of

A

multimeric chromophore-binding phycobiliproteins and non-chromophore-binding linker proteins

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20
Q

List some phycobiliproteins

A
  1. Phycocyanin (PC)
  2. Phycoerythrin (PE)
  3. Allophycocyanin (APC)
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21
Q

What do bilin chromophores do?

A

Bind the polypeptide subunits

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22
Q

Describe bilin chromophores

A

Open-chain tetrapyrroles synthesised from haem

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23
Q

What is the advantage of bilin chromophores?

A
  • expand absorption capabilities of Cyanobacteria
  • efficient light absorption in deep water
24
Q

Charge separation

A

The energy of light is transformed from an excited electron to a negatively charged ion (excitation energy to chemical energy potential)

25
Describe the reaction centre of photosystem II:
- D1 and D2 proteins - ‘special pair’ of bound chlorophylls
26
Why is photosystem II reaction centre known as P680?
Its chlorophylls absorb light most strongly at wavelength 680nm
27
Describe the movement of an electron through P680
- during charge separation, the electron passes to pheophytin - then to bound plastoquinone - then to peripheral plastoquinone - creates P680+
28
P680 regeneration
electron regained from water
29
How can P680 regain an electron form water
It is a strong enough oxidising agent to break the H-O bonds
30
What happens after 4 P680 cycles?
- 2 water molecules are split to generate 4H+ and O2 - electrons captured at the manganese centre
31
What is the ATP and NADPH generated by photosynthesis used for?
Fixation of carbon from CO2
32
What does the Calvin-Benson cycle require to reduce 1CO2 to carbohydrate?
- 3ATP - 2NADPH
33
Photosynthesis evolution
Dramatically changed the path of evolution
34
What did the Great Oxidation Event allow?
Evolution of oxidative phosphorylation
35
What did the evolution of oxidative phosphorylation allow?
- transition from prokaryote to eukaryote - because higher energy demand can be fulfilled by more efficient ATP synthesis mechanism
36
What does a ring structure provide?
Absorbance capacity
37
What is the ground state?
Lowest possible energy state
38
What happens to excited electrons if nothing happens quickly?
Decay back to ground state
39
Describe fluorescence
Light emittance at a higher wavelength than input (changes light wavelength)
40
What type of complex is an antenna complex?
Light harvesting
41
What is the fundamental job of the antenna complex?
To transfer energy to the reaction centre
42
Describe Cyanobacterial photosystems
- photosystems contain chlorophylls - antenna complex contains bilin
43
Why do cyanobacteria need specialised photosystems?
Light absorption is unidirectional (it all comes from above)
44
Why is the ability to absorb violet and red light and evolutionary advantage?
Occupy deeper niches that are less populate, but only receive red and violet light
45
Fluorophore
- fluorescent chemical compound that can re-emit light upon excitation - e.g. chlorophyll
46
Why does fluorescence occur?
If fluorophores are too far away from each other to resonate
47
What does charge separation allow?
Transfer from electron energy of the sun to redox chemistry
48
Where does charge separation occur?
At the ‘special pair’
49
What is pheophytin?
- acceptor molecule - pigment - tetrapyyrol - looks like chlorophyll but lost magnesium in the centre
50
P680 is
Very strong; can rip electrons out of even stable molecules
51
What occurs in photosystem II?
Photolysis
52
Why does photolysis not occur at P700?
- not strong enough to split water - not high enough reduction potential (wrong place on reduction potential scale) - not good enough oxidising agent
53
Z-photosynthesis
The thermodynamically stable flow of electrons downhill through a series of different reaction carriers
54
Why does pheophytin have to be really quick
Lest recombination happens
55
What is the equivalent of cytochrome c in oxidative phosphorylation
Cytochrome b6f
56
What is gluconeogenesis
- glycolysis in reverse - requires ATP and electrons (taken from NADPH)

Michaelmas Term 1 (42 decks)

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