Structure of Chloroplast Video Lecture - NEET

hi it's mr. Andersen and in this video
I'm going to talk about the chloroplast
that's the organelle found in plants
where photosynthesis takes place a great
place to find them would be in the leaf
of a tree so if we look at that in
cross-section we're going to have a
number of cells and these are going to
be the organelles found within that cell
if you've got a structure that we'll
talk about in just a second but it's
important to understand that they're not
fixed within the cell they can move
around and so if we apply a little bit
of light to a cell all of the
chloroplasts will line up so that you
can get the maximum amount of light if
we apply too much light to that cell
they'll hide on the sides of the cell
they're doing that to protect themselves
from damage but they're not alone if we
look at a chloroplast it's going to be
surrounded by a set of mitochondria that
will follow it throughout the cell and
the reason they're following it is they
need the energy they need the energy
that was once in the Sun and is now in
molecules like glucose the structure of
a mitochondria is pretty simple they've
got two membranes around the outside and
then they're filled with stroma it's
going to be this liquid on the inside
inside that liquid we've got ribosomes
they've got their own genome so they
have their own DNA but most of the
action is going to take place along the
thylakoid membrane we have a series of
these membranes and when they're stacked
up it makes a structure inside called
the grana if we look specifically at one
Granum that's where everything is taking
place we have both the light reaction
and the calvin cycle I won't go into the
specifics of photosynthesis but if we
think about the Calvin cycle what's the
function of that well the plant is
taking in carbon dioxide and we want to
add energy to that molecule we're making
something like glucose when I say adding
energy to it what do I mean we're adding
high-energy electrons and so there are
bonds between the carbon and the
hydrogen and glucose and so we have to
add energy to those electrons where is
that energy coming from originally it's
coming from the Sun where is this all
take place it takes place along the
thylakoid membrane so we're going to
zoom in to this rectangle right here and
what we'll find is there's a membrane
but there's also a series of proteins
that's going to be everything in purple
one of the most famous ones is ATP
synthase but we also have these giant
Tanna complexes those are going to be
proteins that are filled with pigments
one of the most famous ones obviously is
chlorophyll and so as we let Sun hit
that membrane what's going on well the
energy of those photons is used to get
the chlorophyll excited and it's passing
its electrons down an electron transport
chain now there's a few other things in
play we've got a series of protons
protons are going to be atoms of
hydrogen that are missing their
electrons and we also have water so
water that's taken in in photosynthesis
and so as these electrons get excited
they move down an electron transport
chain and we really have a hole right
here so we have to get more electrons to
fill that hole and that comes from the
water so watch carefully what happens
right here is that we break that water
apart we're making oxygen that's the
oxygen that a plant gives off we're also
donating these electrons and we're
making some more of these protons if we
watch specifically what happens to one
of those electrons that went really fast
let's go back and look at that again if
we watch that electron what it's doing
is as it moves through this electron
transport chain is it's using its energy
because it's gained energy right here to
pump a proton from the outside to the
inside of the thylakoid membrane now we
have a bunch of positive charges on the
inside they would like to leave and the
only way to leave is to go through ATP
synthase as you do that you generate ATP
let's watch another electron go through
so we see that same thing occur but
where did the electron go well we give
it even more energy after it goes
through this electronic transport chain
and then that electron eventually goes
to a carrier molecule you can see that
everything is positioned perfectly it's
outside the thylakoid membrane in the
stroma and so that energy that was in
the photons has now been converted to
energy in this carrier molecule and in
the ATP where is it going it's going to
the Calvin cycle in the Calvin cycle
we're taking that energy and adding it
to carbon dioxide we're also adding
hydrogen and we're making high-energy
molecules like glucose now where did the
chloroplasts come from if we look at the
chloroplast it's found in all plants
it's very similar to a type of
cyanobacteria the algae that's pictured
right here and if we put those next
each other there are going to be a lot
of structures that are the same between
the two so they're going to have a
double membrane their own genome they're
going to have their own thylakoid
membrane it's almost as if we took a
cyanobacteria and got rid of all its
defenses on the outside and that's how
we think chloroplasts came to be we
think at one time endosymbiosis occurred
we have these cyanobacteria or ancestors
of cyanobacteria that were taken into a
cell now already inside there we had a
mitochondria and previous to that the
mitochondria had been taken into the
cell as well but as we engulf it instead
of breaking down the cyanobacteria the
cell got rid of those phagocytes around
the outside of it and it became the
chloroplast that we have today so what
does a chloroplast do it takes energy
from the Sun to make high-energy
molecules that can be utilized to grow
the plant or to generate ATP inside
mitochondria and I hope that was helpful