Chapter 16 Flashcards
Equation for photosynthesis
6 CO2 + 6 H2O –> C6H12O6 + 6 O2
Photosynthesis equation represents what two processes
light reactions
dark reactions
Light reactions
NADPH and ATP are produced
requires light
Dark reactions
ATP and NADPH provide the energy and reducing power for the fixation of CO2
do not require light energy- can occur in light or dark
Where do the energy-transducing reactions occur
thylakoid membrane
Common chloroplast photoreceptors
chlorophyll b- methyl group replaced by an aldehyde group
chlorophyll- main photoreceptor
carotenoids
absorb in other portions of the visible spectrum and transfer energy to chlorphylls
how do Photosynthetic units work
excited electrons are passed from one chlorophyl to the next until it reaches a reaction center
Goal of light reactions
to generate ATP and NADPH using light energy
Light reaction occur in _____ and involves ___
thylakoid membranes
two photosystems- Photosystem I and II
Light reactions have a series of redox reactions coupled to phosphorylation of ADP to ATP in a process called
photophosphorylation
Photosystem I does what
reduction of NADP+ to NADPH
Photosystem II does what
the oxidation of H2O to O2
Light reaction is
endergonic
driven by light energy absorbed by the chlorophylls of the two photosystems
Photosystem II is a
H+ pump
four photooxidation events in photosystem II oxidize two H2O molecules and produce one O2 molecule
light switches photosystem II’s pair of _____ into _____ and then into _____ upon donation of the e- to PQ
chlorophyll
strong reductant P680
the strongest oxidant P680+
What does P680 oxidized
P680 strips 4 electrons out of water, oxidizing it to O2
Components of the electron transport chain of the thylakoid membrane
Photosystem II
Cyt b6/f
photosystem I
ATP synthase
Cytochrome b6f function
H+ pump driven by electron transport and very similar to complex III from mitochondria
Plastocyanin
functions as a one-electron carrier by cycling between the Cu+ and Cu2+ oxidation states
mobile carrier of 1 e-, like cytochrome c in mitochondria
in linear electron flow, ferredoxin serves as
a substrate for ferredoxin-NADP+ reductase
The core of each photosystem I is a pair of chlorophyll molecules
P700
Electron transport in the thylakoid membrane also creates a proton gradient by ____ methods
three
Methods of making a proton gradient
- proton pumping from the stroma into the thylakoid lumen by the Cyt b6/f complex using the energy of electron transport from photosystem II to Photosystem I
- by splitting of H2O which releases H+ into the thylakoid space for lumen
- when photosystem I reduces NADP+ by using H+ in the stroma to produce NADPH (lowers H+ concentration)
The flow of H+ back to the stroma through ______ provides the energy synthesis of ATP from ADP and Pi
ATP synthase
Steps of photophosphorylation
- proton pumping coupled with the electron transport
- splitting of H2O releases H+
- removal of H+ to make NADPH
Cyclic electron transport in PSI can be coupled to ____ when NADP+ is lacking
ATP production
The calvin cycle takes place in the
stroma of chloroplast
Carbon dark reactions are also known as
Calvin cycle
goal of calvin cycle
fix CO2 by reacting it with ribulose-1,5-bisphosphate to produce two molecules of 3-phosphoglycerate which can make glucose
Calvin cycle
Substrate-
Product-
substrate- CO2
Product-GAP
Glyceraldehyde-3-phosphate
Most abundant protein on earth
Rubisco
Increasing Rubisco activity using genetically engineered plants could
reduce CO2 abundance in the atmosphere and reduce the greenhouse effect
First reaction of the Calvin cycle
carboxylation of six molecules of ribulose-1,5-bisphosphate
the actual carbon fixation step
each carboxylation product splits to give two molecules of 3-phosphoglycerate (12 total)
Rubisco is not a
highly specific enzyme
Photorespiration
fixing O2 rather than CO2 by Rubisco
unavoidable by-product of photosynthesis
is wasteful
C4 pathway- carbon fixation in tropical plants
CO2 enters the outer cells and reacts with phosphoenolpyruvate to give oxaloacetate and Pi- reduced to malate
malate provides a way to move CO2 into the interior cells with lower oxygen thereby avoiding wasteful photorespiration by rubisco in the presence of oxygen
Calvin cycle products are used to
synthesize sucrose
Calvin cycle products are used to synthesize
starch
