L14. Energy Generation in Chloroplasts Flashcards
explain the chloroplasts
- 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
explain the structure of the chloroplasts
- outer membrane
- inner membrane
- thylakoid membrane
chloroplast structure - outer membrane
- more permeable than inner membrane
- similar property as mitochondria
chloroplast structure - inner membrane
- much less permeable than outer membrane
- inner membrane surrounds the stroma (similar to the matrix)
chloroplast structure - thylakoid membrane
- 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
explain both stages of photosynthesis
- 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
stage 1 of photosynthesis
- 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
stage 2 of photosynthesis
- 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
how do chlorophylls absorb light
- 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
how do chlorophylls absorb light - explain the porphyrin ring
- 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
explain the structure of the photosystem
- reaction center surrounded by chlorophyll antenna complexes
- chlorophyll molecules are inside the light-harvesting antenna complexes
photosystem structure - antenna complexes
within the complexes, light energy is captured by one chlorophyll molecule and is transferred to a neighboring one
photosystem structure - reaction center
- 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
photosystem - what happens to the e- after it is transferred from the special pair
- 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
explain photosystem II - proton pump and ATP
- 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
explain photosystem II - O2 production
- 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
explain photosystem I
- a high energy e- is passed to ferredoxin (a mobile e- carrier)
- it is used for NADP+ reduction to NADPH
photosystems - how is ATP and NADPH production powered
- 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)
photosystems - what does plastocyanin do with the e- after PSII
- 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
photosystems - why is both PSI and PSII needed to produce ATP and NADPH
- 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
carbon fixation - where are ATP and NADPH located
- 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
carbon fixation - explain the process
- 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
carbon fixation - what is used to power this process
ATP and NADPH are used as energy and reducing power to regenerate ribulose 1,5 bisphosphate
explain the carbon fixation cycle
it combines CO2 with ribulose 1,5 bisphosphate to form simple sugar
carbon fixation cycle - what is consumed and produced
- consumed: 3 CO2, 9 ATP, and 6 NADPH
- produced: 1 molecule of glyceraldehyde 3-phosphate
carbon fixation cycle - what is glyceraldehyde 3-phosphate
- it is a 3 carbon sugar
- a starting material for other sugars and organic molecules
explain how carbs and fatty acids are stored
- 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
explain the evolution of oxidative phosphorylation - stage 1
- 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
explain the evolution of oxidative phosphorylation - stage 2
- in nutrient poor conditions, it is an advantage to not consume ATP to pump out H+
- this caused the evolution of e- transport
explain the evolution of oxidative phosphorylation - stage 3
- life forms began using nonfermentable acids as e- sources
- with efficiency, the H+ gradient and more energy allowed enhanced ATP production
explain green sulfur bacteria
- 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
explain the relationship between O2 accumulation and aerobic respiration
when aerobic respiration becomes widespread, O2 concentration leveled out
