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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
Q

Describe the reaction centre of photosystem II:

A
  • D1 and D2 proteins
  • ‘special pair’ of bound chlorophylls
26
Q

Why is photosystem II reaction centre known as P680?

A

Its chlorophylls absorb light most strongly at wavelength 680nm

27
Q

Describe the movement of an electron through P680

A
  • during charge separation, the electron passes to pheophytin
  • then to bound plastoquinone
  • then to peripheral plastoquinone
  • creates P680+
28
Q

P680 regeneration

A

electron regained from water

29
Q

How can P680 regain an electron form water

A

It is a strong enough oxidising agent to break the H-O bonds

30
Q

What happens after 4 P680 cycles?

A
  • 2 water molecules are split to generate 4H+ and O2
  • electrons captured at the manganese centre
31
Q

What is the ATP and NADPH generated by photosynthesis used for?

A

Fixation of carbon from CO2

32
Q

What does the Calvin-Benson cycle require to reduce 1CO2 to carbohydrate?

A
  • 3ATP
  • 2NADPH
33
Q

Photosynthesis evolution

A

Dramatically changed the path of evolution

34
Q

What did the Great Oxidation Event allow?

A

Evolution of oxidative phosphorylation

35
Q

What did the evolution of oxidative phosphorylation allow?

A
  • transition from prokaryote to eukaryote
  • because higher energy demand can be fulfilled by more efficient ATP synthesis mechanism
36
Q

What does a ring structure provide?

A

Absorbance capacity

37
Q

What is the ground state?

A

Lowest possible energy state

38
Q

What happens to excited electrons if nothing happens quickly?

A

Decay back to ground state

39
Q

Describe fluorescence

A

Light emittance at a higher wavelength than input (changes light wavelength)

40
Q

What type of complex is an antenna complex?

A

Light harvesting

41
Q

What is the fundamental job of the antenna complex?

A

To transfer energy to the reaction centre

42
Q

Describe Cyanobacterial photosystems

A
  • photosystems contain chlorophylls
  • antenna complex contains bilin
43
Q

Why do cyanobacteria need specialised photosystems?

A

Light absorption is unidirectional (it all comes from above)

44
Q

Why is the ability to absorb violet and red light and evolutionary advantage?

A

Occupy deeper niches that are less populate, but only receive red and violet light

45
Q

Fluorophore

A
  • fluorescent chemical compound that can re-emit light upon excitation
  • e.g. chlorophyll
46
Q

Why does fluorescence occur?

A

If fluorophores are too far away from each other to resonate

47
Q

What does charge separation allow?

A

Transfer from electron energy of the sun to redox chemistry

48
Q

Where does charge separation occur?

A

At the ‘special pair’

49
Q

What is pheophytin?

A
  • acceptor molecule
  • pigment
  • tetrapyyrol
  • looks like chlorophyll but lost magnesium in the centre
50
Q

P680 is

A

Very strong; can rip electrons out of even stable molecules

51
Q

What occurs in photosystem II?

A

Photolysis

52
Q

Why does photolysis not occur at P700?

A
  • not strong enough to split water
  • not high enough reduction potential (wrong place on reduction potential scale)
  • not good enough oxidising agent
53
Q

Z-photosynthesis

A

The thermodynamically stable flow of electrons downhill through a series of different reaction carriers

54
Q

Why does pheophytin have to be really quick

A

Lest recombination happens

55
Q

What is the equivalent of cytochrome c in oxidative phosphorylation

A

Cytochrome b6f

56
Q

What is gluconeogenesis

A
  • glycolysis in reverse
  • requires ATP and electrons (taken from NADPH)

Michaelmas Term 1 (42 decks)

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