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Biochemistry > photosythesis > Flashcards

photosythesis Flashcards

1
Q

basic equation

A

CO2 + H2O –> (CH2O) +O2

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2
Q

photosynthesis

A

the process by which plants utilise light energy to make ‘food’ for themselves

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3
Q

CH2O represents

A

carbohydrate

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4
Q

takes place

A

chloroplast

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5
Q

photosynthesis over view

A

-light photon is absorbed -enery 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 reaction to fix CO2

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6
Q

light dependent reaction

A

purpose is to produce ATP and NADPH for the calvin cycle

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7
Q

calvin cycle

A

light independent cycle–> CO2 fixation

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8
Q

chloroplasts

A

the energy of light captured by pigment molecules, called chlorophyll, in chloroplasts is used to excite electrons giving them great reducing potential

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9
Q

trapping light energy

A

-photoreceptor molecule- chlorophyll a - a substituted tetrapyrole- 4 nitrogen atoms co-ordinate a magnesium ion

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10
Q

structure of chlorophyll a

A

substituted tetrapyrol -4 nitrogen atoms coordinately bonded to a magnesium ion

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11
Q

photoreceptor molecule

A

chlorophyll a

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12
Q

how come chlorophyll is a good photoreceptor

A

has strong absorption bands int he visible region of the spectrum

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13
Q

what happens when light is absorbed by chlorophyll

A

energy from light excites an electron from its ground energy level to an excited level.

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14
Q

what happens to the excited electron

A

if a suitable electron acceptor is enaryby, the excited electron can move from the initial molecule to the acceptor molecule. -this results in a positive charge on the initial molecule and a negative on the charged acceptor molecule

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15
Q

photoindced charge seperation

A

initial molecule becomes positive and the acceptor molecule becomes negative

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16
Q

the site where the separation occurs i called the

A

special pair of chlorophylls in the reaction centre

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17
Q

in plants there are two kinds of membrane bound light sensitive complexes

A
  1. photosystem 1 2. photosystem 2
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18
Q

which comes first in the LIR chain

A

PS 2 (only named this because it was discovered second to PS 1)

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19
Q

Photosystem 1

A

p700 -responds to a light with wavelengths <700nm

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20
Q

photosystem 2

A

p680 -responds to light with wavelengths <680nm

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21
Q

the two photosystems generate a

A

proton gradient

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22
Q

the proton gradient is used to

A

release ATP from ATP synthase -remember H+ do not produce ATP in ATP synthase, they just release it

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23
Q

electrons are derived from

A

H2O–> photolysis

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24
Q

electrons derived from water are used to..

A

reduce NADP+

25
Q

electron flow

A

first flow through PS2, then though the cytochrome bf (a complex homologous to Q cytochrome c oxidoreductase) , and then through PS PS 2–> cytochrome bf —> PS1

26
Q

cytochrome bf

A

a complex homologous to Q-cytochrome c oxidoreductase

27
Q

photosynthetic sequence

A
28
Q

photosynthetic- membrane organisation

A
29
Q

reaction that occurs at PS2

A

2H2O + 4hv –> 4H+ + 4e- + O2

30
Q

by product of Light independent reaction

A

oxygen

31
Q

reaction that occurs at PS1

A

4e-+ 2H+ + 2NADP+ + 4hv –> 2NADPH

32
Q

overall LIR

A

2H2o + 2NADP+ + 8hv –> 2H+ + O2 + 2NADPH

33
Q

how many photon need to be absorbed to make 2 nadph molecules

A

8

34
Q

proton gradient across thylakoid mem linked to ATP synthesis- experiment

A

1966- Andre Jagendorf

  1. -thylakoid membrane were soaked in pH4 buffer for several hours
  2. -then rapidly submerged in pH8 buffer containing ADP and Pi
  3. -the pH inside the thylakoid initially remained at pH 4
  4. -a burst of ATP production was notes that accompanied the disappearance of pH gradient
35
Q

why did a burst of ATP production accompany a disappearance of the pH gradient

A

due to the process of ATP production involving H+n movement through ATP synthase from one side of the thylakoid to the other

36
Q

ATP synthase resembles those in mitochondria

A

CF1 -CF0 complex -orientation is reversed -protons flow out of the thylakoid lured -whereas in mitochondria, protons flow in to the mitochondrial matrix

37
Q

diff between ATP synthase in mitochondria and chloroplast

A

-protons flow out of the thylakoid lime in chloroplasts -protons flow in the mitochondrial matrix -orientation is reveres

38
Q

where are ATP and nADPH released into

A

the stromal space ready for the dark reactions (CO2 –> carbohydrate)

39
Q

carbon dioxide fixation -Calvin cycle occcurs

A

-occurs int he chloroplast stroma

40
Q

the calvin cycle requires

A

2NADPH and 3ATP per CO2 fixed

41
Q

calvin cycle

A

pic

42
Q

description of the CC

A

-CO2 enters and joins with rubisco to form a short lived intermediate. -this then becomes a three carbon molecule called 3-phosphoglycerate -Then 6ATP are oxidised to 6ADP releasing energy to form 1,3bisphosphoglycerate -this is then reduced when 6NADPH is reduced to 6NADP+ to form glyceraldehyde-3-phosphate -at this point a G3P molecule is lost to be used to create glucose and the organic compounds -then regeneration occurs where RuBP is formed–> this involves the reduction of 3ADP to form 3ATP

43
Q

net production in calvin cycle

A

net production of 1G3P molecule requires 9ATP and NADPH

44
Q

how does the LIR have enough NADP+ and ADP

A

ATP and NADPH used in the calvin cycle returns NADP+ and ADP to the light reaction

45
Q

three parts to the CC

A

fixation, reduction and regeneration

46
Q

CO2 is fixed by

A

rubisco (most abundant enzyme on earth) , which reacts CO2 with Ribulose bisphosphate to produce two molecules of 3 phosphoglycerate

47
Q

3-phosphoglycerate is phosphorylated by

A

ATP to form 1,3, bisphosphoglyercate

48
Q

1,3,bisphosphoglycerate is reduced to

A

glyceraldehyde-3-phosphate by NADPH

49
Q

when RuBP is regenerated the byproduct is

A

sucrose or starch

50
Q

ribulose bisphosphate carboxylase oxygenase

A

RUBISCO– most abundant protein int he world- 50% of the soluble protein in a lead

51
Q

regulation of CO2 fixation

A

-CC does not occur in the dark because if they did then the necessary ATP and nADH would have to eb provided by metabolism of stood carbohydrates–> quite recycling

52
Q

why does the CC not occur in the dark

A

would have to metabolise stored carbohydrates to provide enough ATP and NADPH–> futile recycling

53
Q

key enzymes of the calvin cycle that are regulated are

A

-rubisco -fructose 1,6,bisphosphatase (FBPase) -sedoheptulose bisphosphatase (SBPase) these enzymes are found in the stroma

54
Q

control of Rubisco, SBPase and FBPase activity

A

all three enzymes cycle between active forms in the light and inactive forms in the dark -pH optima=8 (for all). In the dark the pH of the storm is 7. Upon illumination, H+ are pumped out of the storm into the thylakoids causing stroll pH to increase to * -pumping of the +vely charged protons into the thylakoids during the illumination causes Mg2+ to leave the thylakoids, consequently stroll [Mg2+] increases. Mg2_ activates all three enzymes -

55
Q

all three enzymes (rubisco, FBPase, SBPase) are activated by

A

Mg2+ - so when +vely charged protons are pumped into the thylakoid during illumination, Mg2+ leaves the thylakoids and the stroll [Mg2+] increases

56
Q

pH and enzyme activity

A

All three enzymes have pH optima=8. In the dark the pH of the stroma is ~7. Upon illumination, H+ are pumped out of the stroma into the thylakoids causing the stromal pH to increase to ~8.

57
Q

how is the active form of rubisco achieved

A

CO2 (not find) reacts with active site lysine of rubisco to make carbamate this is stabilised by Mg2+ to give the active form of rubisco

58
Q

some CC enzymes (FPase and SBPase) can ago through..

A

disulphide bridge to thiol transitions due to having cis residues. The e- for reusing thioredoxin are supplied by Ps1 via ferredoxin

59
Q

one molecule of triode P is produced for every

A

3CO2 fixed

Biochemistry (18 decks)

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