Biology 1A - Lecture 10: Photosynthesis, light

Uploaded by UCBerkeley on 17.09.2012

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\f0\fs29 \cf0 >>INSTRUCTOR: Good morning everybody.Good morning. I hope you had a nice weekend.Next
week, at this time you'll be sitting here and looking at your exam.So, until then we
still have a lot of ground to cover. So I would like to point out again, is that what
is important for the exam is has all been covered in the lectures, up until Friday,
Friday lectures will be included. So when it comes to syllabus, the syllabus has certain
page numbers, that the summaries have certain page numbers that the book has material that
we didn't cover here, that's not important, it is important that you see what's slides
we discussed and if you have questions to the slides they are from the book, so you
can go into the book and the book explains it.Okay.Good.Yes, please?>>STUDENT: [Indiscernible]>>INSTRUCTOR:
No, no, no. All lectures up to until Friday. Including this Friday, all lectures, until
mitosis, yes.Okay.So today\'a0 as a summary, we will have review session tomorrow afternoon
it's a Q and A session, so please come with specific questions and we're going to go through
all of the chapters, there will be extended office hours, starting from today and Wednesday
after this class you can come and leave at any time.So, come in, when it's your turn,
ask your questions when it's answered you can leave again you do not have to sit there
for the entire hour, or two hours, so if you have specific questions, you're welcome to
stop by and verbalize your questions and so today we're going to discuss photosynthesis
but before we do this I want to go back to the last question.Oh, come on.Why isn't it\'a0going?Okay.So,
the last question, how many oxygen molecules are required each time a molecule of glucose
is completely oxidized through carbon dioxide, via anaerobic respiration and so the answer
was 6.72% of you had that right.So, how do you get to the 6?So first, you should think
about how many NADH and FADH are produced from glucose before oxidative phosphorylation
and that's 12 so go to the summary slides, no I don't have it, so you produce 12 NADH
+H plus including one FADH 2, okay.So how many electrons are those?24. Each of those
carries two electrons, so we have a total of 24 electrons.And these 24 electrons combine
with oxygen. Oxygen is O 2.Right?O 2.And becomes water.So, if you have oxygen O 2 how many
waters do you get? 2.H2O. Right for each oxygen that you put in you get 2 waters.And how many
electrons are in two waters? 4.I think I made a mistake there last time.So every proton
also comes from an electron so you have H20 that's two electrons + 2 is 4 electrons, so
all you to do is divide 24 by 4, and that = 6.So we need 6 oxygens.To capture the 24
electrons that are moving through the chain.Okay.So, I would like to come back to the difference
between oxidative phosphorylation that we discussed last time and fermentation that
we discussed last Wednesday. So we have a number of cases, how electrons can move and
how the cell generates energy sit the whole purpose of this, the production of ATP so
the first one is the I aerobic respiration, in that is oxygen is the final electron receptor\'a0so
when you have oxygen around then glucose becomes glyceraldehyde to pyruvate and if oxygen is
present and then the pyruvate gets import into the mitochondria as completely oxidized
to CO2, we are the acetylcholine [Indiscernible] and the whole TCA cycle they're all captured
by NADH and then through the electron transfer chains and Chemiosmosis we release ADP, so
this releases, 32 ATP, there's another another respiration called anaerobic respiration,
and this we did not discuss, so if you have the same pathway, glucose going into the mitochondria
going through all of this, but then the electrons are not donated to oxygen, they are\'a0 they
have a different electron receptor, for example, sulfate.So this is the sulfur bacteria they
use sulfate as the final electron acceptor and when it acceptors electron it becomes
H 2S, hydrogen sulfide. So this is also respiration, because you have an electron transport chain
but you have a different electron acceptor, you do not have this is anaerobic, so it's
at the very end of the electron chain that you have a different acceptor, but in this
case, everything else remains the same, and we have fermentation, in fermentation, neither
oxygen or [Indiscernible] so you still have glucose so you still make ATP but then the
pyruvate is reduced, it accepts the electrons from NADH and we discuss the two cases either
of ethanol or have lactate fermentation, so this because of glycolysis only gets 2 ATP.
But this ATP actually comes from here, right. From glycolysis it doesn't come from here,
from the pyruvate reduction.Yes, please?>>STUDENT: [Indiscernible]>>INSTRUCTOR: That's a good
question. How many ATPs do you make in anaerobic respiration, I would have to look it up I
don't know. So you make more than the 2 ATPs that you make through glycolysis.There's an
electron transfer chain they plump protons out but you do make more, but the precise
numbers, I don't know.Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR: The 30 or 32 will depend on how the NADH from
glycolysis is shuttled into the mitochondria.We discussed that last time.So please look that
up again.Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR: When would anaerobic occur and when would
fermentation occur. Anaerobic respiration is limited to very specific organisms so these
sulfur bacteria they live in hot springs and they have a lot of sulfur around.So, it's
actually evolutionary it's earlier, it was earlier developed than the oxygen respiration,
because about up to 2\'a0billion years ago we didn't have oxygen yet, the oxygen was
made through photosynthesis and before there was photosynthesis there was no oxygen.So
what the organisms did is they used only glycolysis, so only fermentation that was the original\'a0
(No sound).The way of making ATP. And then some bacteria found out that huge capitalize
the electrons and made an electrons transport chain and that's an anaerobic fermentation,
anaerobic respiration start and then they made ATP, and then oxygen occurred on the
planet and than anaerobic respiration was. So you only need to know yeast and [Indiscernible]
cells they can switch between the I robic respiration and the fermentation. The anaerobic
respiration is specialized organism we don't do this for example.Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR:
It does not fall into the same pathway, it has a different electron transport chain but
you don't need to know that though.Okay.One word about so we have have discussed how organisms
can capture energy from glucose. So from carbohydrates, they can also capture energy from the other
things that we eat like proteins if we eat a a steak or tofu or fatty acids if you eat
French fries so they can do this too, so when you ingest proteins they ingested to the amino
acids the amino acids are taken up and they have a nitrogen so the nitrogen gets split
off into ammonia, the ammonia gets then formed into urea and the urea you discreet your urine.
It's the function of the urine to secrete the ammonia that you get from protein digestion,
but the carbon skeleton can feed into these pathways depending on the amino acids so it
can feed into glycolysis and it can feed into the TCA cycle and then it goes through oxidative
phosphorylation and then you get energy from them you didn't need to know the details.
Fats, if you eat fat the fat you know was glycerol that gets split up first, the glycerol
joins the pathway in the glycolysis, the fatty acids are completely oxidized to acetylcholine
and the lost it goes with with the TCA cycle and you get oxidative phosphorylation and
so for fatty acids you make more than 100 ATP and that's why fats are so energy dense
because you're body can generate so much ATP from a fatty acids don't you don't need to
know this particular number. There was a question this morning so the only sort of number that
you should remember is the ATP, right? The 30kilojoule per mol and of course all numbers
when get comes to the pathway, you only need to know the summary slides but they told you,
how many ATPs are formed, how many NADH are formed, etc., so these numbers you should
remember and apply.So, again, other substances like proteins or fats can fuse into the spot
where they be discussed to produce ATP to produce phosphorylation at tend. And then
you have one more slide about feedback inhibition we cut that out and now we move to photosynthesis.So
we had this slide already several times before. So what we discussed what happens in heterotrophs
and plants in the mitochondria organic product are oxidized and the electrons are transferred
to oxygen.That leads to water, and the organic product are oxidized to carbon dioxide. What
we discuss today is how photosynthetic autotrophs produce organic matter by using carbon dioxide
and water. So this is actually the or gin of all of our foods here on the planet whether
they're veg tear or not. Even the meat, organisms they need to obviously eat and in some cases
they eat plant material so all energy from our life comes from the sun and is converted
to these organic molecules.So in essence it's the opt sit to carbon dioxide is reduced to
an organic product and as a by-product and it's really only a by product, oxygen can
released. And we do need oxygen to live but that wasn't the case always on this planet.So
the photosynthesis is there for life for the planet so it is by the plants, by the multicellular
alga and unicellular protists so, there are bacteria that can perform photosynthesis.
As well as the purple sulfur bacteria they don't use water adds the electron donor they
use H 2S, but you don't need to know this. But there are multiple organisms that can
capture the energy from the sun to make sugars.Through these organisms use the organic molecules
to put it into respiration? No. Not all of them.So, here's a summary of the photosynthesis
reaction.You have CO2, you water, the CO2 becomes reduced it accepts electrons to become
the sugar, the water become, oxidized, the sugars are removed it becomes oxygen, so this
is endergonic.And therefore energy is required.For this reaction to occur. And this energy the
energy that is provided is light.Energy that's provided.So you can see it's pretty much the
opposite of respiration, but it's a very different mechanism as you will see.So here you have
the structure of a plant.So photosynthesis occurs in the leaves, can also occur in the
stems but we discuss the leaves you have the mesophyll cells, they're cells that have gashes,
spaces around it.So that the carbon dioxide can actually get to the cell and ten the oxygen
that they produce can get out. So there's gas exchange occurring and that's happening
via these opening in the leaves, the stomata, within the cells, you have the chloroplasts
and the morphology we discussed already, we have the three membranes you the outer membrane,
the inner membrane and then you have the thylakoids. Here these pancake stacks, these are the thylakoids.And
then you have the space in between the thylakoids and the inner membrane so all of this here,
what was that space called? Stroma.Yes.And that's where the reaction will take place
that we discuss today.So photosynthesis is split into two reactions.One is called: The
light reaction, and the other use to be called: The dark reaction.But that is not correct
because the other one requires light and that has to do with the regulation.You're not going
go into detail but it's not called dark reaction anymore.It is called: Carbon fixation. Okay.So
in the light reaction.We have water.And the water is oxidized 2 O 2.And in this process
the electrons are taken through the light reaction and the electrons are used to reduce
NADP +, 2 NADPH + H +.So as you can see there's a slight difference between respiration and
between the light reaction of the photosynthesis. This is NADP and not NAD +, the only difference
is a phosphate group, and the phosphate group sits on the adenine nucleotide so it has nothing
to do with phosphate metabolism it's just another structure.But it is important to know
that photosynthesis has NADP and respiration has NAD +, but both do the same things there
except two electrons and they donate again two electrons so it's a structure issue the
NADP.And in this process, not only NADH is produced from water also ATP is produced.By
forming from ADP to phosphate. So water comes in, oxygen is produced and we get ATP and
reducing equivalent NADH + H +.And these two compounds are then used by the carbon fixation
reaction it's also called: The Calvin Benson cycle and as you might know this was discovered
here in Berkeley and I was actually sitting in the building where Melvin Calvin discovered
the cycle and we used his office as our meeting room. So the ghost of Melvin was around he
got the Nobel Prize in 1964 for that discovery as as you all know the way this works is carbon
dioxide is bound and formed to sugars.And he found out the cycle works.So, major achievement
in life on our planet.So carbon dioxide moves into the cycle, ATP and the electrons from
NADH are utilized and what comes out sugar.And we're going to discuss that too.So, we start
with the light reactions, to today will all be about the light reactions. So water is
split into oxygen and electrons the electrons are accepted by NADP + to form FADH and along
the way, ATP is produced that's what we're going to discuss today, this reaction is performed
by light, the energy for this reaction comes by light, and so I want to discuss with the
physics of light.So, one can describe light as electromagnetic wave or as a discreet energy
particle it is photons. So you here you see the wavelength split up and then there's a
section, a very small section which we can actually see, these are the colors.And then
it moves to light with longer wavelengths such as the infrared the microwave and then
the radio waves which have a wavelength of 700\'a0 up to several hundred meters so you
can can see this is the visual light and that's used by photosynthesis we have the shorter
wavelength on the left, the longer wavelength on the right, but the short herb the wavelength
the higher the energy.Okay, so this one has high energy and this one has relatively speaking
low energy.So as you know for example, here when you go through shorter wavelengths you
have UV light which is very aggressive can do damage in your cells if you go to infrared
light with the higher wavelength that has lower level but it can create to heat and
we use it in heating lamps, etc. So this is the spectrum, and that's also used by doing
photosynthesis.So the first experiments that were done to discover this was an experiment
such as this, the light goings through a prism it splits up the spectra of the light so you
have a visible light spectra here so here's an algae, it's one [Indiscernible] algae and
then the prism but these various light energies here on the algae, and depending on if the
light is useful for photosynthesis the powers of the alga produce oxygen, the oxygen moves
out and the aerobic bacteria will gather as these spots and they gather when these alga
get blue purple light or when they red light, they do not gather when the alga gets green
light. And so this one of the reasons why\'a0 it's the reason why chlorophyll and particularly
leaves look green because that's the only light that is not absorbed by the plant it's
transmitted and reflected and that's why we see green as green because it's not absorbed
there's red, and purple, is absorbed and it's used for photosynthesis.So, from this you
can deduce what is called: The action spectrum.It's the same thing and you just look at here the
rate of the photosynthetic O 2 release and you see it's like the bacteria where there
were wavelengths that were highly absorbed you have a lot of oxygen release and here's
a lot of oxygen release and here's the green [Indiscernible] it's actual the action spectrum
because you measure the action of photosynthesis which is the O 2 release.And then it was found
out that this\'a0 these wavelengths that are affected in performing photosynthesis, is
performed by pigments.And there are several pigments, the chlorophylls there's chlorophyll
A, chlorophyll B and the carotenoids.All of these are lipophilic structure and we go into
the structure and as you can see this is the absorption of these pigments.Absorption spectra,
so you can see at what wavelength does a pigment absorb light and therefore can use it and
you can see chlorophyll A absorbs light in the 400 end, chlorophyll B does it in different
wavelengths it's a little bit higher here and a little bit lower here and the carotenoids
they absorb in this region here.They do not absorb in the orange red region, so carrots
have a lot of carotenoids that's why they look orange because they absorb all light
but orange.Sigh there's no carotenoid here. So they can absorb the light energy and all
of these pigments are used to utilize the light energy to produce oxygen.So here you
see a structure of a chlorophyll. So the chlorophyll has a what is called: A porphyrin ring this,
is this organic ring here its carbon, nitrogen, it's these rings right here it's magnesium
so when you eat a lot of vegetables you eat loot of magnesium because they have a lot
of magnesium in the center and then it as a hydrogen carbon tail, so there are hydrogen
carbon, it's a very hydrophilic molecule so it can form into hydro [Indiscernible] proteins.
I'm going to show you this to you be because the most important feature of the molecule
it has a long con you gaited system, do you know what that is from chemistry? It's where
you have a double bond and single bond next to each other, so you see this is a congregated
system here and it's very long.Not this.Okay, it's very long congregated system where the
electrons cover around, not in the structure but in general. And so this has a unique property
when it comes to absorbing light.Because then you have a chlorophyll molecule, and it's
emit by a photon, by light.This congregate electron and this congregated system gets
excited and it moves up the energy of the electron. So the electron gets excited.And
then the electron falls back, and when it falls back it releases the same energy that
is absorbed when light came. So what can it do? So it can release it as a photon again
that would be florescence, you see this here as a bacteria that will shine with light and
the chlorophyll electrons they fall back and light is emitted again, so you have florescence.It
can also release the energy as heat.Yeah.Or, it ask take the energy and move it to another
chlorophyll molecule. Which has another electron that gets excited.And this process of moving
one excited state of an electron to excite another chlorophyll to another electron is
residence transfer, it it's the energy that was ash sod by the chlorophyll molecule it
can be transferred to the next molecules.Simply by excitation of dropping molecules. Excitation
and dropping back, and the next molecule, excitation and dropping back.And so in the
end, you what is called: A photosystem.So the photosystem is the light harvesting complex.That's
associated with a reaction center. So we have one reaction center but basically it's protein
it it's in the membrane, it sits in the membrane of the thylakoid, so these are these stacked
pancakes it sits in between and in this protein we have two parts, we have the light harvesting
complexes that surround the reaction center.And in the light harvesting complexes we have
the chlorophyll molecules, the chlorophyll molecules absorb the light, the faux photon
the electron jumps up, falls back energy is next to the chlorophyll and the energy jumps
around until it gets to a special pair of chlorophyll A molecules in the special section
of the reaction center and they're light in a specific way because of the proteins that
surround it.And when that happens, again, and electron is excited, but it's so excited
that it jumps off.Okay. So it gets so excited that the electron doesn't fall back it's going
to be moved and if an electron is moved we call that oxidation.Yeah. So we have light
is harvested, jumps around until it's bundled in the reaction center in the reaction center
the electron jumps off and leaves.Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR: How is the special
pair chlorophyll different? Structurally they're the same. But they're head in place with the
proteins that surround them and that's a special place, the structure is the same.Yes?>>STUDENT:
[Indiscernible]>>INSTRUCTOR: Do you\'a0 how many photons do you need for this? One photons.\'a0.One
photon moves in, jump jump jump, kick electron out.So one electron is moved with one photon.>>STUDENT:
[Indiscernible]>>INSTRUCTOR: Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR: Energy transfer
and chloroplast, yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR: Yes.>>STUDENT: [Indiscernible]>>INSTRUCTOR:
Oh.So, that's a very good question, so how efficient is this energy transfer from the
chloroplast molecules? It's not 100% efficient so never everything is 100% efficient\'a0so
you release some energy as heat. But if you have a photon and you release some energy
as heat what happens is your wavelength becomes longer.Right. Because it's less energy. Soon
the wavelength will become longer as they move along until they hit the reaction center.What's
the efficient rate? I don't know. But basically, what you should think about the light harvesting
complex, is a basically a solar collector, it\'a0 the main function of this light harvesting
complex it covers a wider area in the membrane so it can collect the photon molecules, the
reaction is very small it's the central molecule. So all places photosynthesis can be absorbed
and energy can be [Indiscernible] into the center.So, iClicker question.We should have
two today. I think, depending on how far we get. So which of the following statements
of chlorophyll is false?Okay.Here are the statements: And go now.Okay. Few more seconds.Click
now.And 97% had it right. Yep was relatively straightforward. Where's my pen?There's not
only one form found in plants there are multiple forms so this one is correct.The other ones
were wrong. So there was a question?>>STUDENT: [Indiscernible]>>INSTRUCTOR: So what is the
form of the energy transfer between the chlorophyll molecules? It depends on the association.
It could be light, it's usually not heat. Because you lose too much. It diffuses out.
If they're very close proximity the energy transfer can be directly leads to the molecule.So,
now we get to the photosystems. So this is the same slide that I showed you before.You
have the light harvesting complex here in purple. You have the chlorophyll molecule
sitting in here they capture light it jumps around until it hits this very specific reaction
center and then the electron is kicked out and the electron is captured by the primary
acceptor. Now in this one here, the two chlorophyll molecules that are very specifically aligned
they're also called: Reaction center P 680. And P 680 is because they absorbed a wavelength
of 680\'a0nanometers were specific, precise 680 nanometers so this is then photosystem
two.And so in photosystem two we have the P 680, and the P 680 molecules lose the electrons
so they become P 680 +. Yeah, they literally lose they're molecules\'a0 electrons so they're
oxidized.And so now comes the second part of the reaction now you have an oxidized P
680. You a P 680 +, and that is a very strong oxidation agent. And so, it takes electrons
from water and that's where the water comes in.So it captures the electron from water
to fill up the gap, so the P 680 becomes reduced again and goes back to its ground state, P
680.And so, in this reaction, oxygen is formed as a byproduct and two protons because the
electrons are taken. Water has two electrons, so therefore P 680 under goes two cycle, because
it only releases one electron so it has to jump two times to kick the electrons out.
And that's how water is [Indiscernible] you release oxygen and protons.So, we have the primary acceptor, I'm not going
to discuss what that molecule is, that is now reduced, and accepted the electron from
the chlorophyll it donates the electron to intermediates and this this is [Indiscernible]
so it's plus the I can known so it is also floats through the membrane and shuttles electrons
across.It then goes to a cytochrome complex that accept it is electron and gives the electrons
to cyanine which is another soluble protein so they go down a chain just like respiration
and they go down the chain with the energy. So that make it is primary acceptor ready
to accept the next electron.Yeah, so it donates electrons and moved through and it can accept
the next electron from water. But [Indiscernible] is not the send the actually is NADP, which
is reduced to NADPH + H +.And now we have a problem because the free energy of the plus
cyanine here is lower than the NADP so it cannot reduce it so what the plant does is
a second photosystem in here that jumps up, boosts the energy of the electron again and
then it gets to NADP H, so the second system is called: Photosystem 1 even though it comes
after photosystem 2 but that's for historical purposes and it has the light harvesting complexes
with the chlorophylls they capture light, they jump around until they have hit a very
specific chlorophyll molecules the electron is excited and jumps off to another acceptor,
in this case ferredoxin and then the electrons are transferred to the NAD to produce NADPH
so we started with water electrons are moving through photosystem 2, cytochrome complex,
photosystem 1 and in photosystem 1 the reaction center is called P 700 because that particular
one absorbs the energy at 700\'a0nanometers so it's slightly different than that one.In
photosystem 1, they get a boost, they move to the primary acceptor ferredoxin and then
we finally have NADPH.>>STUDENT: [Indiscernible] because water can move through electrons that's
why two electrons have to be moved.So the way that it works is\'a0 the chlorophylls
only move one electron at a time. So one electron is kicked down the lane and then the\'a0 the
second photon is absorbed the electron gets excited and drops off and then the second
electron from water moves along it's very complicated how water is split but they can
only one do one every time. So per electron transfer you need 2 photons and per water
you need 4 photons.Because it comes from two electrons.Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR:
That comes afterwards. We get to that, yes.>>STUDENT: [Indiscernible]>>INSTRUCTOR: So, you need
the\'a0 the problem is, that the\'a0 the free energy of the molecules that accept the electrons
they're very low. So the reaction for example from chlorophyll to plastoquinone is endergonic
so in order to make it happen you need the light energy and when it accepts the light
energy it's boosted and kicked off but it as a higher energy than it had before and
then it can go down the lane, but unfortunately needs a second boost to get to NADPH.So you
need two boosts to increase the free energy that can form an exergonic reaction afterwards.What
is the purpose of?>>STUDENT: [Indiscernible]>>INSTRUCTOR: Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR:
So why do we need also photosystem 2? Because unfortunately photosystem 1 is the free energy
is not low enough to take the electrons from water. You couldn't move electrons from water
in photosystem 1, that won't work, you need the photosystem 2 to split the water.So for
example, some bacteria, they don't require photosystem 2 because they don't use water
as the electron donor and then it works and then you only need one photosystem, but when
it's split you need a second system.Yes?>>STUDENT: [Indiscernible]>>INSTRUCTOR: You need two
photons, one for photosystem 2, one for photosystem 1 for the electron to move through the chain.But
water comes with two electrons and therefore you need 4 photons, 2 x 2 to get 1 NADP +
H +.So, what is the purpose of all of this? The purpose is now we have NADPH, so that's
great.Right, at the end, water is split, we release oxygen now we have NADPH but that's
not the only purpose, so here again is exactly the same thing I just showed you, we have
photosystem 2 at the beginning.Light is absorbed, lite is split, oxygen is released electrons
move, plastoquinone it's a [Indiscernible] protein plus the cyanine, goes to photosystem
1.Photosystem they move to ferredoxin, NADPH is reduced to NADPH + H +.And that's what
you need to know about the photosystem is summarized here.The components of it.So, in
addition to that, and that's now important, somebody asked what happens to the two protons
here?Well, you have protons, you increase your proton gradient and further more, the
cytochrome complex here, when the electrons move it moves 4 protons from the stroma, into
the thylakoid space so you get an additional 4 protons move so that's analogous to respiration
so we have the [Indiscernible] that shuffle protons around, so the free energy that is
generated when is liberated when the electrons move is used to shovel protons from one side
to the other and again it's against the gradient.We have here in the thylakoid space inside of
the pancake it becomes more and more acidic the proton gradient will increase.And outside
it becomes alkaline it stays neutral so the protons are moves to make a acidic environment
inside of the thylakoid.And just like with respiration, that proton gradient that has
been created against the gradient is used by the ATP synthase to produce ATP, the protons
move back you have the turbine T turbine rotates the subunit, ATP and phosphate are squished
together and it makes ATP.Same thing, nearly same molecule, same mechanics in [Indiscernible].
So, we get two things out of this reaction. NADPH and ATP, and then both of those are
utilized in the Calvin Benson cycle to fix carbon dioxide.And so, I think, yep so now
we're going to see it as a movie so you see how the electrons move.So I hope you have
the system on.Now, you don't.Tim, could you have a look please.Yep. Now, you have it on.Okay.
We're fine?And we're going to do special effects.So, this time, from my favorite TV show.Okay.[VIDEO]>>INSTRUCTOR:
All right.[Applause]So which TV show was that? Game of Thrones. Very good.Okay. So I'm going
to show it again and then we're going to go through the mechanics of what's happening.Yes,
so we have the chloroplast, we have the thylakoid and what we're talk tact thylakoid membrane,
right? Here.That's why where you have the 4 system, the photosystem 2 you have the cytochrome
BF and in this case the ADP synthase that produces the ATP. So here in green you have
the light harvesting complexes. Right. So that's where all of the chlorophyll molecules
said they absorb the energy of a photon, electron gets excited that's why the shake and then
the energy is transferred until you get to the special pair of chlorophylls, special
fill of chlorophylls they gets so excited that the electron moves to an acceptor, and
eventually that becomes the plastoquinone that's down there. So the same thing happens
again, photons excite the special pair, a second electron moves and so the plastoquinone
is reduced and can drift off.So, where do the electrons come from now. You have water,
the 4 red dots are manganese molecules that lead to the splitting of water and one electron
after the other is utilized to reduce again the chlorophylls so they become neutral.In
the meantime the plastoquinone moves to the cytochrome BF, it transfers, shovel protons
along the way into the inside of the chylocide(?) they move to plastocyanin, it they boost,
they absorbed from the chlorophyll molecules in the middle, that donates electrons first
becomes, oxidized and then accepts the electron from the plastocyanin.Then it moves to ferredoxin
and that finally forms NADPH + H +, that the proton gradient that has been accomplished
across the membrane, in particularly inside of the thylakoid you have a high proton gradient
that's used here for the turbine, to make ATP production. To produce ATP.And that's
the end of that.Okay.Question?>>STUDENT: [Indiscernible]>>INSTRUCTOR: The question is where do the protons come
from? That's a very complicated question, and I'm not going to go into detail the important
part is a proton gradient is performed. But protons are not moved until the ATP synthase
hit it's the electrons that move through all of the components including plastocyanin that's
all about electrons, not about protons. And we continue on Wednesday. \