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Biochemistry 2 > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

how do plants make glucose?

A

light + H2O + CO2 –> O2 and glucose

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2
Q

2 stages of photosynthesis

A

Stage 1: light reactions

Stage 2: Calvin cycle

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3
Q

Light reactions

A

solar energy (photons) –> chemical energy (ATP, NADPH)

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4
Q

The Calvin cycle

A

chemical energy (ATP, NADPH) –> G3P (glucose precursor

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5
Q

where does photosynthesis occur?

A

in the chloroplast

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6
Q

chloroplast structure

A

2 membranes that surround a fluid called stroma

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7
Q

thylakoid

A

sac suspended within stroma (liquid)

thylakoid membrane holds chlorophyll

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8
Q

grana

A

stack of thylakoids

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9
Q

chlorophyll and photons

A

if chlorophyll absorbs an electron of a specific wavelength, one electron enters an excited state

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10
Q

photosystem

A

chlorophylls sit inside a photosystem and the excitation can be passed from molecule to molecule

excited electron goes back to ground state and releases a new photon to excite the next electron

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11
Q

reaction center complex

A

contains a special pair of chlorophyll a molecules

when it is struck with a photon, it transfers an ELECTRON to the primary electron acceptor

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12
Q

how do you reduce the final chlorophyll that donated its electron to the primary electron acceptor?

A

H2O becomes O2 to reduce final chlorophyll

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13
Q

stroma

A

outside thylakoid membrane

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14
Q

lumen

A

inside thylakoid membrane

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15
Q

light reaction purpose

A

use light energy to produce NADPH and ATP

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16
Q

where do light reactions occur

A

along thylakoid membrane in chloroplasts

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17
Q

light reactions type of reaction

A

series of redox rxns beginning with H2O oxidation into O2

very unfavorable, so energy comes from light

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18
Q

final rxn of light reactions

A

NADP+ reduced to NADPH

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19
Q

photophosphorylation

A

ADP + Pi –> ATP

20
Q

Dark reaction aka Calvin cycle purpose

A

use ATP and NADPH (from light rxn) to make glucose

21
Q

dark rxn aka Calvin cycle location

A

stroma (outside thylakoid membrane, inside chloroplast)

22
Q

dark rxn aka Calvin cycle main focus

A

reduce CO2 to glucose (carbon fixation)

23
Q

Photosystem II (PSII) overview

A

H2O –> O2 + H+

in thylakoid lumen

24
Q

PSII where do electrons go

A

from H2O to cytochrome b6f

25
Q

Plastocyanin (PC)

A

carries electrons from PSII to PSI (middle man)

26
Q

Photosystem I (PSI) overview

A

electrons go from P700* to Ferrodoxin (Fd) and to Flavoprotein (FAD) then to NADP+ to make NADPH

27
Q

where does NADP+ become NADPH

A

stroma!

28
Q

PSII and PSI contribute to establishing…

A

proton (H+) gradient

29
Q

light reactions are UF or F

A

very unfavorable!

so light provides energy

30
Q

Z scheme overview

A

electrons are removed from water, passed through PSII and PSI and end up in NADPH

  • creates ATP
  • light must be absorbed once in each PS
31
Q

PSII

A

1) light is absorbed by a pigment
2) energy is passed inward from pigment to pigment until reaching the rxn center
3) At rxn center, energy is transferred to P680, boosting electron to a high energy level
4) the high energy electron is passed to the primary electron acceptor and replaced with an electron from water
- O2 is released
5) electrons go to Pheo then PQ to cytochrom b6f to PC (plastocyanin)

32
Q

ATP synthesis

A

1) high energy electron travels down electron transport chain (loses energy as it goes)
2) some released energy drives pumping of H+ ions from stroma into thylakoid interior, creating a gradient
3) As H+ ions flow down their gradient into the stroma, they pass through ATP synthase, driving ATP production (chemiosmosis)

33
Q

PSI

A

1) electron arrives at PSI and joins P700 special pair of chlorophylls in rxn center
2) when light energy is absorbed by pigments and passed inward to rxn center, electron in P700 is boosted to very high energy level and transferred to an acceptor molecule then to Fd, FAD
3) the special pair’s missing electron is replaced by a new electron from PSII (comes from ETC)

34
Q

NADPH formation

A

1) high-energy electron travels down a short second leg of the electron transport chain
2) at the end, the electron is passed to NADP+ (along with a second electron from same pathway) to make NADPH

35
Q

what do we use ATP and NADPH from light rxns for?

A

to produce sugar in the Calvin cycle!

36
Q

transfer of electrons from PSII to PSI and PSI to NADPH do what with energy?

A

release energy! spontaneous, bc electrons in P680 and P700 are boosted to high energy levels when they absorb energy from light

37
Q

path when an electron leaves PSII (the electron transport chain)

A

electron is transferred to plastoquinone (Pq) –> cytochrome complex (Cyt) –> plastocyanin (Pc)

38
Q

excited P700: ETC

A

excited P700 is a good electron donor

  • it sends electrons down a short ETC
    1) electron is passed to Ferredoxin (Fd), then NADP+ gains electrons to become NADPH
39
Q

plastoquinone (PQ)

A

takes H+ from stroma and pumps them to the thylakoid lumen

40
Q

Higher reduction potentials

A

PC (things further down the cycle) have higher reduction potentials (don’t want to give up their electrons)

41
Q

FAD role

A

takes NADP+ and H+ (from stroma) to make NADPH

42
Q

overall H+ concentrations

A

increase H+ in lumen, decrease H+ in stroma

43
Q

Calvin cycle location

A

stroma of chloroplast

44
Q

Calvin cycle step 1

A

1) 6 ribulose-1,5-bisphosphate to 12 3-phosphoglycerate
(add 1 CO2 to each ribulose-1,5-bisphosphate)

enzyme: Rubisco

45
Q

Calvin cycle step 2

A

2) 3-phosphoglycerate into 12 1,3-BPG (using 12 ATP) and then 12 G3P (using 12 NADPH to 12 NADP+)
2 G3P can enter gluconeogenesis to make glucose

46
Q

control of Rubisco

A
  • optimal pH is 8 (pH of stroma upon illumination)
  • stimulated by Mg2+ (required metal ion) that moves to stroma as H+s are pumped into the thylakoid space
  • Rubisco activase stimulates Rubisco
47
Q

increased NADPH and calvin cycle

A

increased NADPH activates some Calvin cycle enzymes

Biochemistry 2 (32 decks)

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