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MSF2 - Photosynthesis > Introduction > Flashcards

Introduction Flashcards

1
Q

What are the two main types of photosynthesis?

A

Rhodopsin homologs and Reaction centre based photosynthesis

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2
Q

Where is most rhodopsin based photosynthesis done?

A

In archaea

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3
Q

What colour is the rhodopsin pigment in archaea?

A

Rhodopsin give the membrane a purple colour.

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4
Q

How is ATP generated following rhodopsin based photosynthesis?

A

Protons pumped across the membrane during photosynthesis flow back through ATP synthase to generate ATP.

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5
Q

Describe the structure of rhodopsin.

A

GPCR fold - 7 TM helices.

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6
Q

Describe the retinal cofactor of bacteriorhodopsin in the inactive state.

A

Trans retinal

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7
Q

What happens to retinal following light activation of bacteriorhodopsin?

A

Photoisomerisation - to 13-cis retinal.

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8
Q

Describe the key chemiosmosis experiment performed using bacteriorhodopsin.

A

Put bacteriorhodopsin and mitochondrial ATPase in a vesicle - spaced at a distance from one another. When light was shone on the membrane, ATP was produced.

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9
Q

Describe features of photosynthetic reaction centres.

A

Involve 5 TM domain proteins, often involve pseudodimers, derived from a common ancestor. Usually have an antenna region fused to the RC protein or located close by.

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10
Q

What are the reaction centre types? And what are they named after?

A

Type 1 (named after PSI) and Type 2 (named after PSII)

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11
Q

What are the terminal electron acceptors for the two types of reaction centre?

A

Type 1 - FeS cluster

Type 2 - quinone

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12
Q

Why does oxygenic photosynthesis require two enzymes, one of each reaction centre types?

A

Oxidising water requires a lot of energy - both reaction centres are needed to provide enough energy to split water and still have some left for carbon fixation.

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13
Q

What is the general equation for photosynthesis?

A

CO2 + 2H2A -> [CH2O] + H2O + 2A (where A is oxygen or sulfur)

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14
Q

Where does the free oxygen come from in the general equation for photosynthesis?

A

From the substrate water

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15
Q

Where did oxygenic photosynthesis evolve from?

A

Cyanobacteria

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16
Q

How can eukaryotes become photosynthetic?

A

By endosymbiosis with cyanobacteria.

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17
Q

Is the photosynthesis reaction endogonic or exergonic?

A

Endogonic - requires light energy.

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18
Q

What change in atomosphere was the carboniferous era responsible for?

A

More oxygen and high levels of coal formation.

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19
Q

Why do carbon dioxide levels fluctuate throughout the year?

A

When carbon dioxide reduces, it is thought to be due to the photosynthesis of plants in the northern hemisphere in the summer.

20
Q

Describe the membranes in cyanobacteria.

A

Plasma membrane has normal respiratory chain and cyanobacteria also have a complex internal membrane system (like thylakoids).

21
Q

What is special about thermophilic bacteria?

A

Their proteins are very stable and tend to crystallise easily.

22
Q

What is the pH on either side of the thylakoid membrane in cyanobacteria?

A

pH 8 - outside of the thylakoid

pH 5 - inside the thylakoid membrane

23
Q

What are chloroplasts derived from?

A

Endosymbiosis of cyanobacterium - this was monophyletic, meaning it only happened once.

24
Q

Describe the structure of the chloroplast.

A

5μm ellipsoid structure. Outer membrane and inner membrane;

  • continuous thylakoid membranes form stacks called grana
  • grana linked by stromal lamellae
  • stroma is the equivalent of cyanobacterial cytoplasm
25
Q

Where are PSI and ATP synthase located within the thylakoid membranes?

A

In the stromal lamellae because they project from the membranes more - cannot fit within grana.

26
Q

Where are PSII and Cytochrome b6f found within the thylakoid membranes?

A

PSII tends to be in the granal regions. Cytochrome b6f is distributed evenly throughout the membrane.

27
Q

What did EM tomography tell us about the structure of the thylakoid membrane?

A

Shows spiral staircase arrangement of continuous thylakoid membrane.

28
Q

Name some photosynthetic eukaryotes.

A

Higher plants, green algae, red algae and brown algae.

29
Q

What gave rise to the different types of algae?

A

Secondary and tertiary endosymbiosis events.

30
Q

Where are chloroplasts found and why?

A

Just underneath the mesophyll cell layer so that they can capture light easily.

31
Q

What is the minimum energy requirement per photon in photosynthesis?

A

Red photon - 680 nm.

32
Q

What happens if a blue photon is absorbed during photosynthesis?

A

The equivalent energy to a red photon is used and the extra energy provided by the blue photon is lost as heat.

33
Q

How do antennae regions increase the efficiency of light harvesting?

A

Couple thousands of pigments to the reaction centre so that the reaction centre can be excited many times per second.

34
Q

What happens to an antenna pigment when absorbing a photon?

A

This exciton makes downward energy jumps around the antenna region until it reaches the reaction centre where it can perform the chemistry of the reaction.

35
Q

What other pathways can excited state electrons undergo (if not absorbed by an antenna pigment)?

A

Photochemical reactions, red fluorescence and resonance transfer to an acceptor molecule.

36
Q

In decreasing energy levels, name the different coloured absorbing pigments.

A

highest energy is blue absorbing, then orange and red.

37
Q

What are the major light harvesting pigments?

A

Chlorophylls a and b

38
Q

Describe the structure of chlorophylls a and b.

A

Porin ring with a long hydrophobic phytol side chain. Lots of conjugated double bonds which absorb in the visible region of light.

39
Q

Why is it difficult to get chlorophyll in solution? How is this overcome?

A

It has a long phytol side chain. Can get into solution if within a membrane or bound to another protein.

40
Q

What are the accessory pigments?

A

Carotenoids and bilins

41
Q

Where are bilins found and what are they similar to?

A

Found in cyanobacteria. They are essentially an open chlorophyll molecule as they are linear tetrapyrroles.

42
Q

What is the main light harvesting protein in plants?

A

LHC2 - associated with PSII

43
Q

What are the major light harvesting proteins of cyanobacteria?

A

Phycobiliproteins which contain bound bilin pigments.

44
Q

Describe the phycobilisome.

A

Contains thousands of different coloured pigments that act as a funnel to the reaction centre. Fill in all gaps in the absorption spectrum - this makes a dense culture of cyanobacteria appear black.

45
Q

How are proteins in the thylakoid membranes connected?

A

By mobile electron carriers that can diffuse through the whole membrane system.

MSF2 - Photosynthesis (6 decks)

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