Download Light Dependent Reactions

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* How are
chloroplast similar to the
mitochondria? How are they different?
* https://www.youtube.com/watch?v=AcX2n1rC4
W4
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* To identify the reactants and products of the
light dependent reaction
* To determine the mechanism involved in
transferring energy from light to ATP and
NADPH
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* Visible light is
radiation (which is
the transmission of
energy through space
as a wave or particle).
* It is a small section of
what we call the
electromagnetic
spectrum.
* Electromagnetic
radiation travels in
packets called
photons.
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* Pigments can absorb
photons that have the right
energy level to excite the
atom or molecule.
* Photons that are not at the
right energy are reflected.
* reflected colours are those
our eyes perceive on an
object.
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* Integral to the thylakoid
membrane are
photosystems, which are
protein-based complexes
composed of dozens of
photosynthetic pigments.
* When a photon of the
right energy hits a
pigment, it transfers the
energy to the reaction
centre.
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* 1. A photon hits Photosystem II
and releases an electron from
the reaction centre (called P680
because of the light it absorbs).
* 2. This causes a chain of redox
reactions whereby stronger and
stronger *oxidizing agents take
the electron from the molecule
before it in the chain.
* 3. Successive transfer of the
electron allows for hydrogen to
be pumped across the thylakoid
membrane into the lumen by the
cytochrome complex.
* 4. The original electrons lost
from P680 are replenished by
splitting a water molecule. O2 is
formed through this reaction!
* Successive oxidations
by increasingly
electronegative
molecules results in
an electron transport
chain.
* As potential is
decreasing along the
chain, this energy can
be harnessed to do
work, such as
pumping ions.
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* 4. the electrons that
were passed down the
chain end up in the
reaction centre of
Photosystem I (P700),
and another photon is
needed to re-energize it
so it can be released.
* 5. The chain ends in the
reduction of a molecule
of NADP+ into NADPH.
At this point, there is a
large gradient of H+ across
the membrane, as well as
some high energy NADPH
electron carriers.
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* ATP Synthase uses the electrochemical gradient
(from H+) that has been built up in the
thylakoid lumen to catalyze the addition of Pi
to ADP to create ATP. The Proton Motive
Force (or PMF) is what drives this reaction.
* https://www.youtube.com/watch?v=XI8m6o0g
XDY
* When it results from energy from light, such as
in this case, we call ATP synthesis
photophosphorylation.
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* Create a list of all the reactants and products
from these reactions (exclude enzymes,
proteins, cofactors, and other components of
the membrane, as they are not used up).
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* A secondary pathway has been adapted for periods
of low NADP+ in the chloroplast. We call it cyclic
electron flow (as opposed to non cyclic electron
flow just described).
* In this pathway, only Photosystem I is used.
* Photons excite the electrons in P700, which reduce
the cytochrome complex which can pump Hydrogen
ions.
* As a hydrogen ion gradient is still being built up,
ATP synthase can catalyze ATP synthesis.
* No NADP+ is needed in this mechanism, but as a
result, no NADPH is formed.
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* The end result in both cases is ATP. Though
normally, the chloroplast is also able to reduce
NADP+ into NADPH as well.
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* https://www.youtube.com/watch?v=sQK3Yr4Sc
_k
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* 1. Look up the molecules involved in electron transport in the
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thylakoid membrane and be amazed at how many there are (you
don’t need to know any specific names aside from maybe the
cytochrome complex).
2. Where does O2 come from in Photosynthesis?
3. Do one (or more) of the following:
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A) Find a good video that shows all the steps in sequence, without
going into too much detail. Share it with your classmates on facebook,
or by sending it to me.
B)Create a rhyme or mnemonic that helps to remember the steps in
the LDR.
C)Draw a diagram (without copying another!) that shows the steps in
the LDR.
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