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Metabolic regulation > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

What are NADPH and ATP used for?

A

Carbon assimilation reactions to recude CO2 to trioses and more complex compounds from trioses

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2
Q

How is post translational import of proteins regulated?

A

Transit peptides on proteins
Chaperones
Protein import complexes

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3
Q

Permeability in the inner and outer membrane of envelope?

A

Inner (selectively)

Outer (Freely)

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4
Q

What is contained within the stroma?

A

Enzymes for photosynthetic carbon assimilation including rubisco

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5
Q

What are the components that requite proteins synthesised on cytosolic ribosomes and destined for plastids due to plastid transit peptide?

A
  • Stroma
  • Inner envelope membrane
  • Photosynthetic membranes: Thylakoids
  • Thylakoid lumen
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6
Q

What do chaperone proteins do?

A

regulate correct folding of proteins

eg HSP70 keeps protein unfolded to allow passage through protein import apparatus

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7
Q

What are the protein import apparatus?

A

Toc proteins: translocase of the outer chloroplast envelope
Tic Proteins:
Translocase of the inner chloroplast envelope

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8
Q

What is the hill equation?

What is A and give example

A

2h20+ 2A—–> 2AH2 + O2
A: artificial electron acceptor (Hill reagent)
example: DCPIP

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9
Q

How does DCPIP work?

A

When leaf (wit DCPIP) is illuminated
It will go from blue to colourless
With no light no colour change
first evidence that light enrgy caused electrons to flow from H2O to e- acceptor.

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10
Q

WHat is the biological acceptor in chloroplasts?

A

NADP+

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11
Q

What are transit proteins recognised by?

A

secondary structure

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12
Q

What does inport into plastids for proteins require?

A

Specific N terminal signal sequence

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13
Q

How does translocation into chloroplast of protein destined for STROMA work?

A

Protein associated with cytosolic chaperone.
(keeps it unfolded etc)
Transit peptide associates with receptor site on import apparatus.
Protein moves through apparatus into stroma. Transit peptide is cleaved stromal chaperone ensures correct folding.

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14
Q

Translocation across the chloroplast envelope of proteins destined for the thylakoid lumen or lumenal face of thylakoid membrane.

A

Protein has two transit peptides (chaperones work the same)
enters in to stroma same way as before first peptide is cleaved to expose second one.
Second one allows recognition of protein by import apparatus on thylakoid membrane . Once in lumen cleaved

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15
Q

Explain SEC pathway?

A

uses proteins SECA and SECY
SECA is a ATPase moves in and out of thylakoid membrane
SECA allows protein translocation through channel protein SECY
example: Plastocyanin

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16
Q

pH pathway?

A

uses enegry of pH gradient between stroma and lumen
energy from light capture pumps protons across thylaoid membrane causing lumen to be higher than stroma
movement of H back into stroma synthesises ATP
eg for water splitting complex

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17
Q

SRP pathway?

A

protein binds to stromal SRP (signal recognition particle) associates with import apparatus.
Energy from GTP hydrolysis and pH gradient
eg translocation of light harvesting chlorophyll binding proteins of photosystems.

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18
Q

What is between the two Photosystems (I andII)

A

Cytochrome complex (Cyt b6/f)

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19
Q

What are the two kinds of chlorophyll?

A

Chlorophyll a and b

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20
Q

What is p700?

A

PSI

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21
Q

What is p680?

A

PSII

22
Q

explain “photosynthetic pigments are conjugated molecules”

A

they contain alternating single and double bonds

23
Q

Structure of Chlorophyll a

A

Very hydrophobic

interacts eith lipids of thylakoid membrane anchoring the light absorbing molecule.

24
Q

how are chlorophyll a and b arranged in the antenna?

A

Inner part of antenna rich in Chl a

Outer part of antenna rich in Chl b

25
Q

structure of a photosystem?

A

Core complex contains reaction centre( where primary charge separation takes place)
Core complex surrounded by antenna containing light harvesting complexes (LHC) each with 3 light harvesting complex polypeptidesand associated pigmetns
only chl molecules associated with reaction centre are specialised to transduce light intp chemical energy.

26
Q

How do molecules absorb light energy and transfer in to reaction centre

A

resonance transfer

27
Q

excitation by light?

A

light excites antenna molecule raises e- to higher energy level.
Excited antenna passes energy to neighbouring chlorophyll exciting it
enegry transfered to reaction centre chlorophll exciting it
this reaction centre chlorophyll then passes electron to electron acceptor
electron hole in reaction centre filled by donor electron

28
Q

z scheme equation

water to NADP+ electron flow

A

2h20+ 2NADP+ +8Photons —-> O2 + 2NADPH +2H+

29
Q

what are the two proteins associated with e- transport in PSII?

A

D1 and D2

30
Q

How id P680 re reduced?

A

in thylakoid lumen manganese ions on proteins (water splitting complex) accept electrons from water this yield oxygen.

31
Q

WHat is OEC

A

oxygen evolving complex water- splitting complex)

32
Q

WHere is OEC bound?

A

D1 and D2 proteins of PSII reaction centre

33
Q

Where are CFo 1 and 3 encoded?

A

Chloroplast genome

34
Q

Where is CFo 2 encoded?

A

Nuclear genome

35
Q

Where are components of CF1 encoded?

A

chloroplast or nucleus

36
Q

How many photons needed per photosystem to break bonds in water?

A

4 per photosystem

8 photons total

37
Q

How much energy does NADPH conserve ( used t excite electrons)

A

~32%

38
Q

In electron transport chain where do all protons come from?

A

2 at photosystem 2 because of lysis of water

2 after movement of e- from PQH2 to cyt b

39
Q

How does cyclic electron transport work?

A

PSI (p700) transfer electrons to ferredoxin then back to cytochrome complex to PC instead of reducing NADP+
PC then donates electrons to P7– which transferd them to ferredoxin
No net NADPH formation and no evolution of O2
Produces more ATP and less NADPH than the non cyclic pathway
regulated ratio of ATP and NADPH

40
Q

Lateral Heterogeneity?

A

Unequal distribution of thylakoid protein complexes

41
Q

Why lateral heterogeneity is needed?

A

enegry needed for PSI is less than PSII.
If PSI and PSII were next to eachother excitons from antennae could excite PSI leaving PSII under excited interupt pathway.

42
Q

Lateral heterogeniety

where are PSI atp synthases and PSII located?

A

PSI and ATP synthases are in unstacked regions (stromal thylakoids) has access to stromal ADP and NADP+
PSII STAcked granal Thylakoids
mediates tight association of thylakoid mmebranes in grana

43
Q

Control of distribution of excitation energy between PSI and PSII
by phosphorylation of LHCII: REGULATION
Plasticity of the arrangement of the thylakoid membrane

A

Association of LHCII with PSI and PSII
Depends on light conditions.
State 1: Unphosphorylated (Thr) state of
LHCII exclusively associated with PSII.

State 2: Excess excitation of PSII than of
PSI, leads to over production of reduced
PQ which activates a kinase causing
Phosphorylation (Thr) of LHCII.
LHCII Complex becomes negatively 
charged, and  causes unstacking.

Part of LHCII population migrates from granal
to stromal thylakoids: causes therefore a
reduced size of PSII antennae.

Change in relative size of ratio of PSI
and PSII antennae to respond to imbalance
of excitation of the two photosystems

44
Q

Two enzymes in the reduction stage?

A

3 phosphoglycerate kinase

Glyceraldehyde 3 phosphate dehydrogenase

45
Q

What does 3 phosphoglycerate kinase do?

A

Catalyses transfer of phosphoryl group from ATP to 3 PGA to form 1,3 bisphoglycerate

46
Q

What does glyceraldehyde 3 dehydrogenase do?

A

reduction using NADPH causes Glyceraldehyde and pi to be formed

47
Q

Where is the small subunit of rubisco encoded?

A

nucleus

undergoess post translational import into the chloroplast stroma

48
Q

Where is the large subunit of rubsico encoed?

A

Chloroplast

49
Q

Where is the catalytic site of rubisco

A

LSU

50
Q

How is rubisco activated?

A

non enzymic carbamylation of a specific lys residue in presence of Mg2+
carbamylation requires the ATP dependent removal of RuBP from rubisco this is catalysed by activated Rubisco activase

51
Q

Name a Rubisco inhibitor

A

CA1P

52
Q

How is carbamate formed?

A

Lysine reacts with CO2

Metabolic regulation (3 decks)

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