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Genes, Molecules & Cells > Photosynthesis > Flashcards

Photosynthesis Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is photosynthesis?

A

A reverse of oxidative carbohydrate metabolism

  • light energy drives carbon reduction
  • Carbohydrate produced serve the producing organism & consumers

2H20 =(light)= O2 + 4H+

Electrons then reduce CO2

4H+ + CO2 = CH20 + 4H2O

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2
Q

What are the features of the chloroplast?

A
  • Thylakoids (Thylakoid space and membranes)
  • Chloroplast envelope (outer and inner membrane plus intermembrane space)
  • Stroma
  • Granal thylakoids
  • Nucleoids
  • Ribosome
  • Plastoglobules
  • Starch granules
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3
Q

What are the sizes of the chloroplast?how many per algal plant cells?
features of the membranes?

A
  • 5 micrometres approx.
  • 1-1000 per cell
  • ‘impermeable’ inner membrane
  • permeable outer membrane
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4
Q

What is chlorophyll? Features

A

The principal photoreceptor

  • act as light-harvesting antennas
  • highly conjugated bonding system (networks of alternating single & double bonds) so is an excellent receptor
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5
Q

What happens at the Light Harvesting Complex? (LHC)

A

Light energy is absorbed and travels along the antenna pigments to the reaction centre. This then receives donor electrons and emits acceptor electrons

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6
Q

How is light transformed to chemical energy?

A

1) Electromagnetic radiation is propagated as ‘photons’
- Electrons can dissipate its excitation energy by ‘Resonance Energy Transfer’

2) By photooxidation

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7
Q

What are the 2 reaction centres? Where are they located?

A
  • Photosystem II (Oxidises h20, special pair: P680)
  • Photosystem I (Reduces NADP+, special pair: P700)

The electrons from PSII to PSI by an ‘electron transport chain’
-Operate in electrical series coupling oxidation with reduction

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8
Q

What light does PSI respond to?

A

lightwaves <700nm which creates a biosynthetic reducing power in the form of NADPH
-Electrons from 2NADPH come from 2h2o

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9
Q

What is the cytochrome b6f complex?

A
  • Electrons travel from PSII to PSI
  • Homologous to Complex III (oxidative phosphorylation)
  • Generates a H+ gradient
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10
Q

What light does PSII respond to?

A

lightwaves <680nm

  • generates a molecule of O2
  • transfer from h2o to plastoquinone
  • Generates a H+ gradient
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11
Q

What are the features of Photosystem II?

A

A very large protein assembly (20subunits)

  • Catalyses the transfer of e- from h2o to plastoquinone
  • reassembles ubiquinone
  • cycles between oxidised (Q) to reduced (QH2)

-Electrons in QH2 are at a higher redox potential than in H20 (light drives the reaction thermodynamically uphill)

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12
Q

What does P680 do?

A

Extracts electrons from h2o at: -Oxygen Evolving Complex

  • Each time photon kicks electron from P680, e- is extracted from Mn centre
  • 4 photons absorbed to ‘extract’ 4e-
  • 4e- used to reduce 2Q to 2QH2
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13
Q

How is a proton gradient obtained across the membrane?

A
  • Quinone reduction on stroma side of PSII
  • Site of water oxidation on the lumen side

Creates a proton gradient from lumen side to stroma side

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14
Q

What is the ctyochrome bf complex?

A
  • Catalyses the transfer from plastoquinol (QH2) to plastocyanin (Pc)
  • Helps the proton gradient due to enzyme positioning as cytochrome bf reduces platoquinol to plastocyanin (takes up 2H+ and reoxidises on the stromal side)
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15
Q

What happens at PSI?

A

Electrons from P700 travel down through chlorophyll to FeS cluster then transferred to Ferredoxin

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16
Q

What happens at Ferredoxin?

A

-Transfer electrons to NADP+ which is catalysed by ‘ferredoxin-NADP+ reductase’ on the stromal side (enhances proton gradient)

17
Q

How does phosphorylation of ATP come from this?

A

The result of photosynthesis is a transmembrane proton gradient where there is greater protons in the

18
Q

How does phosphorylation of ATP come from this?

A

The result of photosynthesis is a transmembrane proton gradient where there is greater protons in the thylakoid lumen
-This is capitalised upon by the chloroplast ATP synthase which couples dissipation of proton gradient to enzymatic synthesis of ATP

19
Q

How many ATP are produced?

A
  • Non-cyclic transport: 1ATP per photon
  • NADPH indirectly produces 2.5ATP
  • 1ATP for every 3 protons through Chloroplast ATP Synthase
20
Q

How do plants receive carbohydrates in the dark?

A

Calvin Cycle

Stage 1: 3 moluecules of RuBP react with 3CO2 which ultimately creates 6 molecules of Glyceraldehydes-3-phosphate (GAP) and uses 9ATP and 6NADPH

-The GAP can be used for biosynthesis for carbohydrates

Stage 2: Carbon atoms of remaining 5 GAP are rearranged into 3 RuBP

21
Q

What is the enzyme used to fix CO2 in Calvin Cycle?

A

Ribulose Bisphosphate Carboxylase (RuBP Carboxylase)

22
Q

What veriables effect the rate of Calvin Cycle?

A

1) pH level (stroma increase to pH 8.0 in light near RuBP optimum)
2) Mg2+ influx to balance the charge caused by H+ stimulates RuBP

23
Q

How is RuBP production affected in the dark?

A

CAP1 is produced in the dark, inhibiting RuBP Carboxylase

24
Q

What is the ferredoxin-thioredoxin reductase system?

A

Responds to the soluble ferredoxin in stroma

-Thioredoxin system deactivates phosphofructokinase (PFK) to glycolysis

25
Q

What is the overall stoichiometry of Calvin Cycle?

A

3CO2 + 9ATP + 6NADP -> GAP + 9ADP + 8Pi + 6NADP+

26
Q

How is GAP used to make larger carbohydrates?

A
  • The primary product of photosynthesis

- Can be converted into fructose-6-phosphate then in G1P which is the precursor to higher order carbohydrates

27
Q

What are the features of alhpa-amylose?

A
  • starch component
  • synthesised in the chloroplast stroma
  • storage of glucose units
  • starch synthase transfers the glucose residue to alpha-amylose molecule which is driven by PPi hydrolysis
28
Q

What other components other than starch can be produced?

A

Cellulose and Sucrose

Genes, Molecules & Cells (29 decks)

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