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Cell Bio > L14. Energy Generation in Chloroplasts > Flashcards

L14. Energy Generation in Chloroplasts Flashcards

1
Q

explain the chloroplasts

A
  • they have light-capturing pigments (chlorophyll)
  • during the day: photosynthesis produces ATP and NADPH
  • these products are then used to convert CO2 to sugar via carbon fixation
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2
Q

explain the structure of the chloroplasts

A
  • outer membrane
  • inner membrane
  • thylakoid membrane
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3
Q

chloroplast structure - outer membrane

A
  • more permeable than inner membrane
  • similar property as mitochondria
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4
Q

chloroplast structure - inner membrane

A
  • much less permeable than outer membrane
  • inner membrane surrounds the stroma (similar to the matrix)
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5
Q

chloroplast structure - thylakoid membrane

A
  • within the stroma
  • they are folded membranes that are thought to be connected from stacks called grana
  • light capturing system, electron transport chain, and ATP synthase are located here
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6
Q

explain both stages of photosynthesis

A
  • stages 1 and 2 are tightly linked and regulated by feedback mechanisms
  • some carbon fixation enzymes are inactivated in the dark and reactivated by light
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7
Q

stage 1 of photosynthesis

A
  • light reaction
  • after the absorption of light, high energy electrons come from chlorophyll
  • electron transport chain in thylakoid membrane harnesses energy to pump H+ into the thylakoid space
  • resulting gradient drives ATP synthesis
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8
Q

stage 2 of photosynthesis

A
  • dark reaction
  • ATP and NADPH from step 1 drives sugar synthesis from CO2
  • begins in the stroma by production of glyceraldehyde 3-phosphate
  • the products are then exported to the cytosol to produce sucrose and other molecules
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9
Q

how do chlorophylls absorb light

A
  • they absorb blue and red light
  • chlorophyll molecules have a porphyrin ring
  • the molecule also has a hydrophobic tail that holds it in the thylakoid membrane
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10
Q

how do chlorophylls absorb light - explain the porphyrin ring

A
  • light is absorbed by electrons that are distributed in a decentralized cloud around the ring
  • the light excites the e-, perturbing their distribution
  • this perturbed high-energy state is unstable so chlorophyll will get rid of the excess energy
  • this energy is passed onto photosynthetic proteins
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11
Q

explain the structure of the photosystem

A
  • reaction center surrounded by chlorophyll antenna complexes
  • chlorophyll molecules are inside the light-harvesting antenna complexes
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12
Q

photosystem structure - antenna complexes

A

within the complexes, light energy is captured by one chlorophyll molecule and is transferred to a neighboring one

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13
Q

photosystem structure - reaction center

A
  • it is a transmembrane complex of proteins and pigments
  • within the reaction center: chlorophyll dimer special pair
  • it holds e- at a lower energy and traps the energy
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14
Q

photosystem - what happens to the e- after it is transferred from the special pair

A
  • the special pair transfers the e- to electron carriers
  • the special pair will become positively charged
  • the e- carrier then becomes negatively charged
  • the carrier then passes the high-energy e- to the e- transport chain
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15
Q

explain photosystem II - proton pump and ATP

A
  • when light is absorbed, e- is passed onto the mobile e- carrier plastoquinone
  • the carrier will transfer the e- to the proton mump
  • the movement of e- is used to generate an electrochemical gradient
  • the gradient is then used to synthesize ATP
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16
Q

explain photosystem II - O2 production

A
  • an e- is returned to the positive special pair by a water splitting enzyme that extracts e- from H2O
  • the enzyme will hold onto 2H2O while the e- are removed one at a time
  • once the 4 special pairs are restored, O2 is released
17
Q

explain photosystem I

A
  • a high energy e- is passed to ferredoxin (a mobile e- carrier)
  • it is used for NADP+ reduction to NADPH
18
Q

photosystems - how is ATP and NADPH production powered

A
  • movement of e- along the photosynthetic e- transport chain powers the production
  • the e- removed from water by PS II are passed through a H+ pump, then to plastocyanin (mobile e- carrier)
19
Q

photosystems - what does plastocyanin do with the e- after PSII

A
  • it carries the e- to PSI and replaces the special pair e-
  • light is then absorbed by PSI and it causes the e- to be boosted to a very high energy level
  • this then causes the reduction of NADP+ to NADPH
20
Q

photosystems - why is both PSI and PSII needed to produce ATP and NADPH

A
  • the combined actions boost e- to energy levels needed to produce ATP and NADPH
  • them working in tandem effectively couples their 2 e- energizing steps
21
Q

carbon fixation - where are ATP and NADPH located

A
  • they remain in the stroma bc it is impermeable to the inner membrane
  • instead, ATP and NADPH are used to make sugars that are exported by carriers in the inner membrane
22
Q

carbon fixation - explain the process

A
  • happens during the dark reactions
  • because carb production from CO2 and H2O is unfavorable, CO2 fixation is done by Rubisco (an enzyme)
  • the enzyme is able to do this bc of a continuous supply of energy rich ribulose 1,5 bisphosphate
  • as ribulose 1,5 bisphosphate is consumed by the addition of CO2, it needs to be replenished
23
Q

carbon fixation - what is used to power this process

A

ATP and NADPH are used as energy and reducing power to regenerate ribulose 1,5 bisphosphate

24
Q

explain the carbon fixation cycle

A

it combines CO2 with ribulose 1,5 bisphosphate to form simple sugar

25
Q

carbon fixation cycle - what is consumed and produced

A
  • consumed: 3 CO2, 9 ATP, and 6 NADPH
  • produced: 1 molecule of glyceraldehyde 3-phosphate
26
Q

carbon fixation cycle - what is glyceraldehyde 3-phosphate

A
  • it is a 3 carbon sugar
  • a starting material for other sugars and organic molecules
27
Q

explain how carbs and fatty acids are stored

A
  • glyceraldehyde 3-phosphate can be converted to, and stored as starch granules or fat droplets in the stroma
  • it can then be broken down and ultimately lead to ATP production
28
Q

explain the evolution of oxidative phosphorylation - stage 1

A
  • early life forms used fermentation as an ATP source
  • they excreted acids into the environment and that lowered the pH so H+ can be removed from the cell
  • this may be the ancestral ATPase
29
Q

explain the evolution of oxidative phosphorylation - stage 2

A
  • in nutrient poor conditions, it is an advantage to not consume ATP to pump out H+
  • this caused the evolution of e- transport
30
Q

explain the evolution of oxidative phosphorylation - stage 3

A
  • life forms began using nonfermentable acids as e- sources
  • with efficiency, the H+ gradient and more energy allowed enhanced ATP production
31
Q

explain green sulfur bacteria

A
  • it uses H2S (hydrogen sulfide) as an e- donor instead of H2O bc H2S has a higher redox potential
  • only 1 photosystem needed for NADPH reduction
  • the photosystem resembles PSI
  • S is a byproduct instead of O2
32
Q

explain the relationship between O2 accumulation and aerobic respiration

A

when aerobic respiration becomes widespread, O2 concentration leveled out

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