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BIO1332 - Biochemistry > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

What is photosynthesis?

A

All free energy utilized by biological systems arises from solar energy that is trapped by the process of photosynthesis

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2
Q

BASIC EQUATION for photosynthesis?

A

CO2 + H2O → (CH2O) + O2

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3
Q

Where does photosynthis take place?

A

In the chloroplast

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4
Q

Where does oxidative phosphorylation?

A

In mitochondria

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5
Q

What is the thylakoid membrane consisted to be analogous to?

A

The mitochondrial cristae

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6
Q

Give an overview of photosynthesis:

A
  • Light photon is absorbed
  • Energy used to drive an electron from water to generate NADPH
  • Also drives protons across a membrane
  • These protons drive ATP synthesis.
  • The ATP and NADPH are used in the light independent reactions (Calvin cycle) to fix CO2.
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7
Q

How is light energy trapped?

A
  • Photoreceptor molecule – chlorophyll a

- Four nitrogen atoms co-ordinate a magnesium ion

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8
Q

What is light absorbed by in photosynthesis?

A

chlorophyll

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9
Q

What happens when light is absorbed?

A
  • Chlorophylls have strong absorption bands in the visible region of the spectrum
  • Energy from light excites an electron from ground state to an excited energy level
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10
Q

What happens after light is absorbed?

A

Electron is transferred to an acceptor

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11
Q

What is photosynthetic unit?

A
  • Large number of chlorophyll

- 2 types of chlorophyll

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12
Q

What are the two types of chlorophyll?

A
  • 300 antenna chlorophylls (harvest light and transfer excitation energy to)
  • Reaction centre chlorophyll (undergo photochemistry)
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13
Q

Under normal conditions the reaction centre turns over how many times per second?

A

100

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14
Q

What does antenna chlorophyll do to the reaction centre?

A

Increase capacity

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15
Q

What happens once light is funnelled to the reaction centre chlorophyll?

A
  • Excitation electron can move to the acceptor molecule

- Positive charge on donor molecule and negative charge on acceptor molecule

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16
Q

What is photo induced charge separation?

A

Formation of a +ve charge on the donor molecule and a -ve charge on the acceptor molecule

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17
Q

What are the sites where separation occur in photosynthesis?

A

Special pair of chlorophylls in the reaction centre

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18
Q

How is the photosynthetic apparatus arranged?

A

To make photo induced charge separation extremely efficient

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19
Q

What are the two types of membrane bound light-sensitive complexes in photosynthesis in green plants?

A 
Photosystem I (PS I) P700
Photosystem II (PS II) P680
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20
Q

What wavelength of light does PS I respond to?

A

< 700 nm

21
Q

What wavelength of light does PS II respond to?

A

< 680 nm

22
Q

What do photosystems generate?

A

A proton gradient

23
Q

What is a proton gradient?

A
  • Electron flow
  • Electron are derived from H20 and reduces NADP+
  • Electrons first flow through PS II, then cytochrome bf then to PSI
24
Q

What is cytochrome bf?

A

a complex homologous to mitochondrial complex III

25
Q

What is the overall result from photosynthetic electron transport?

A

2H2O + 2NADP+ + 8 hv  2H+ + O2 + 2NADPH

26
Q

How many photons need to be absorbed to make 2 NADPH molecules?

A

8

27
Q

What is the proton gradient across the thyklakoid membrane linked to?

A

ATP synthesis

28
Q

What experiment idd Jagendorf do in 1966?

A
  • Thylakoid membranes were soaked in pH 4 buffer for several hours.
  • Then rapidly submerged in pH 8 buffer containing ADP and Pi.
  • The pH inside the thylakoids initially remained at pH 4.
  • A burst of ATP production was noted that accompanied by the loss of the pH gradient.
29
Q

What does ATP synthase resemble?

A

Those in mitochondria

30
Q

What is ATP synthase?

A
  • ATP synthase – CF1-CF0 complex
  • Orientation is reversed
  • Protons flow out of the thylakoid lumen
  • Protons flow into the mitochondrial matrix
  • Both ATP and NADPH are released into the stromal space ready for dark reactions (CO2 → carbohydrate)
31
Q

What drives ATP synthesis?

A

The proton gradient across the Thylakoid membrane

32
Q

Where does the Calvin cycle occur?

A

Chloroplast stroma

33
Q

What does the Calvin cycle uses from the light reactions to fix CO2?

A

Products:

ATP and NADPH

34
Q

How many NADPH and ATP does theCalvin cycle need per CO2 fixed?

A

2 NADPH

3 ATP

35
Q

What does the net product of 1 G3P require?

A

9 ATP

6 NADPH

36
Q

What are the three components of CO2?

A
  • Fixation
  • Reduction
  • Regeneration
37
Q

What is CO2 fixed by?

A

Enzyme rubisco

38
Q

What happens when CO2, ribulose bisphosphate and enzyme rubisco react?

A

Produces two molecules of

3-phosphoglycerat

39
Q

What is 3-phosphoglycerate phosphorylated to by ATP?

A

1,3 bisphosphoglycerate

40
Q

What is 1,3 bisphosphoglycerate reduced by to make glyceraldehyde-3-phosphate (G-3-P)?

A

By NADPH

41
Q

What is glyceraldehyde-3-phosphate (G-3-P) used to regenerate?

A

Ribulose bisphosphate

42
Q

What is Ribulose Bisphosphate Carboxylase Oxygenase?

A
  • One of the most abundant proteins in the world

- Produces 2 molecules of phosphoglycerate from ribulose bisphosphate and CO2

43
Q

what is regulation of CO2 fixation?

A
  • Calvin cycle does not occur in dark
  • Key enzymes regulated
  • Enzymes found in chloroplast stroma
44
Q

Why does the Calvin cyclin not occur in the dark?

A

Necessary ATP and NADPH would come from metabolising stored carbohydrates. This would be futile cycling.

45
Q

What are the key enzymes which are regulated in the Calvin cycle?

A
  • Rubisco
  • Fructose 1,6 bisphosphatase (FBPase)
  • Sedoheptulose 1,7 bisphosphatase (SBPase)
46
Q

How are Rubisco, SBPase and FBPase controlled?

A
  • Active in light
  • Inactive in dark
  • pH optima = 8
  • Mg2+ activated enzymes
47
Q

How does the increase in light activated the following enzymes Rubisco, SBPase and FBPase activity?

A
  • Light
  • H+ are pumped from the storm to the thylakoids causing stroll pH to rise to 8
  • Mg2+ increases concentration in stromal
  • Activating enzymes
48
Q

How else are SBPase and FBPaseother than light regulated in the Calvin cycle?

A

Disulphide bridge to thiol transitions

-E- for reducing thioreedoxin are supplied by PSI via feerdoxin

49
Q

What is CO2 captured by?

A

Rubisco

BIO1332 - Biochemistry (19 decks)

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