Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MSF2 - Photosynthesis > Light Reactions > Flashcards

Light Reactions Flashcards

1
Q

Where is the photosynthetic electron transport chain found?

A

Across the thylakoid membranes in chloroplasts.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is photosynthesis endothermic?

A

A lot of energy is needed to oxidise water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the two components of the proton motive force?

A

Membrane potential and pH difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the proton motive force dominated by in photosynthesis?

A

pH gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the products of photosynthesis that are later used by the Calvin cycle?

A

ATP and NADPH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the cofactors found in PSII?

A

P680, Pheophytin, Qa, Qb, Mn cluster and Tyr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does PSII do?

A

Uses 4 photons of light to remove 4 electrons from water, generating a proton gradient.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the net effect of PSII activity?

A

To transport 4 reducing equivalents across the membrane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How many electrons are carried by plastoquinone?

A

2 electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Where is plastoquinone reduced and oxidised?

A

Reduced by PSII. Moves out of PSII to Cytochrome b6f (it is membrane soluble). Oxidised in Cytochrome b6f during the Q cycle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the structure of cytochrome b6f.

A

Homodimer where each dimer consists of cytochrome f, cytochrome b6, Rieske centre and Subunit IV.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does cytochrome f contain?

A

Heme c

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does cytochrome b6 contain?

A

Two heme b molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does the Rieske centre in cytochrome b6f contain?

A

An iron-sulfur cluster - [2Fe-2S]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the net effect of cytochrome b6f actvity?

A

Translocation of 8 protons - contributes to proton motive force.
Reduction of two PC per quinol from PSII

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What enzyme is cytochrome b6f homologous to and why?

A

Complex III in mitochondria - both use a Q cycle, oxidise a quinone and reduce a mobile electron carrier.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What happens to the plastoquinone molecules produced in cytochrome b6f?

A

One diffuses back to PSII and one is used to reduce plastocyanin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the Q cycle in cytochrome b6f needed?

A

To mediate electron transfer between PSII and PSI

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How many protons are pumped across the membrane by PSII and cytochrome b6f?

A

12 in total - 4 by PSII, 8 by cytochrome b6f.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is plastocyanin?

A

A single electron carrier, where Cu(I) is reduced to give Cu(II). Plastocyanin is soluble and acts as a mobile electron carrier between cytochrome b6f and PSI.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the result of the distorted tetrahedral coordination in plastocyanin?

A

Gives copper an unusually high potential compared to an isolated copper ion.

22
Q

What happens if cyanobacteria or green algae are copper starved?

A

Plastocyanin is replaced with cytochrome c6 (contains heme c groups).

23
Q

Describe the structure of PSI in cyanobacteria.

A

Trimeric

24
Q

Describe the structure of PSI in eukaryotes.

A

Monomeric

25
Q

What type of reaction centre is present in PSI?

A

Type 1 - terminal electron acceptor is an FeS cluster.

26
Q

What cofactors are found within PSI?

A

chlorophylls, accessory chlorophylls, 2 quinones, 3[4Fe-4S] centres

27
Q

What is the active pigment in PSI?

A

P700 - consisting of two chlorophyll a molecules.

28
Q

Why is PSI unable to oxidise water?

A

The P700 pigment absorbs a longer wavelength than the P680 pigment in PSII, providing less energy - not enough to oxidise water.

29
Q

What type of chemistry is performed by PSI?

A

1 electron chemistry

30
Q

Give an overview of the electron transfer steps that occur in PSI.

A
  1. Electron transfer from plastocyanin to P700
  2. Electron transfer from P700 to chlorophyll a
  3. Electron transfer from chlorophyll a to quinone bound at position A1
  4. Electron transfer from the quinone to FeS clusters
  5. Electron transfer from FeS to ferredoxin
31
Q

What is ferredoxin?

A

A soluble single electron carrier. Contains an Fe2-S2 cluster.

32
Q

What are the major pathways for the electrons from reduced ferredoxin to go to?

A

Ferredoxin-NADP reductase (FNR), Cyclic electron flow, flavin-thioredoxin reductase.

33
Q

What are the minor pathways for the electrons from reduced ferredoxin to go to?

A

Nitrate reductase, nitrogenase, sulfite reductase and glutamate synthase.

34
Q

What cofactor is used by ferredoxin-NADP reductase?

A

FAD

35
Q

Where is FAD found and what does it do?

A

Located spatially close to the FeS of ferredoxin. Acts as a sequential 2 electron carrier:
FAD -> FADH* -> FADH2

36
Q

What is NADPH and when is it used?

A

2 electron carrier, also essentially a hydride carrier. Used in anabolic reactions and acts as a source of reductants in the Calvin cycle.

37
Q

What is meant by the Z-scheme?

A

Non-cyclic electron flow from water to NADP+

38
Q

What happens during cyclic electron flow?

A

Ferredoxin/NADP are used to reduce plastoquinone and this is catalyses by ferredoxin-plastoquinone reductase. Still results in proton translocation, but no net generation of NADPH. Only contributes to the proton motive force.

39
Q

When does cyclic electron flow happen?

A

When there are already sufficient reducing equivalents available for use in the Calvin cycle.

40
Q

Why is the proton motive force mainly dominated by pH in the thylakoids?

A

H+ ion movement into thylakoid is counterbalanced by Mg2+ ions moving out of the thylakoid membranes, this means there is neutral charge across the membrane.

41
Q

What happens to plastoquinol (delivered from PSII) in cytochrome b6f?

A

It is reoxidised to give plastoquinone.

42
Q

How are reaction centre cofactors bound to PSI?

A

Within 11 TM helices.

43
Q

Why is PSI considered to be simpler than PSII, despite the fact that they are homologous enzymes?

A

PSI performs 1 electron chemistry which is simpler than the 4 electron chemistry performed by PSII.

44
Q

What is catalysed by nitrogenase and where is it found?

A

Catalyses the reduction of nitrogen to give ammonia, requiring lots of reducing electrons. Found in some cyanobacteria.

45
Q

Why is NADPH more useful than reduced ferredoxin?

A

Ferredoxin is only a one electron carrier, and is therefore not useful in driving many reactions. NADPH is a two electron carrier and can be more widely used.

46
Q

When is NAD(H) used?

A

During catabolic reactions

47
Q

How does photoactivation of P680 in PSII allow the removal of electrons from water?

A

Activation of P680 removes one electron from the pigment. This makes the pigment electronegative enough to remove an electron from water. 4 photons of light are therefore needed to remove all 4 electrons.

48
Q

Give an overview of non-cyclic photosynthetic electron transport.

A

Light absorbed by antenna pigments of PSII and PSI
Absorbed energy is then transferred to the reaction centre pigments - P680 in PSII, P700 in PSI.
Activation of P680 removes one electron from the pigment - allows removal of e from water.
Electron is transferred from PSII to Cytb6f by plastoquinol (PQ)
Generates a proton gradient – used to drive ATP synthase
Electron transferred from Cytb6f to PSI by plastocyanin (PC)
Activation of P700 excites the electron to a higher redox potential to reduce ferredoxin (Fd)
Fd reduces FAD which is used to reduce NADP+
Generates ATP and NADPH which are used in the Calvin cycle

49
Q

What is the function of ATP synthase?

A

Uses the proton gradient to drive ATP synthesis.

50
Q

How many protons need to be translocated in order to produce one molecule of ATP?

A

3-4

MSF2 - Photosynthesis (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions