Krebs Cycle : Tissues - Science, Class 9 Video Lecture

the second step of aerobic respiration
goes by many different names some
textbooks will call it the citric acid
cycle others will name it after the guy
who discovered it the Krebs cycle or
I've even seen it referred to as the TCA
cycle which stands for tricarboxylic
acid cycle no matter what name you go by
it's that all the same thing it's the
final breakdown of glucose after the
glucose was initially split in half by
glycolysis now it happens in the matrix
part of the mitochondria and the
ultimate yield of the Krebs cycle for
every one glucose that enters the cell
it gives you a pair of ATP s8 NADH is
and a couple of fadh2s I'll discuss what
those are a little bit more in just a
moment but first I want to help make
sure that you understand what's going on
now if we take a look at any living
organism that's a eukaryote ie it has a
nucleus
it'll have somewhere in the cell
mitochondria like this plant cell you
can see it has mitochondria and that's a
trick question that a lot of teachers
like to stick you with they'll ask you
which cells have mitochondria and they
want you to say jost animal cells but
remember plants do aerobic respiration
to break down the sugar that they
themselves are making for their own
purposes so if we take a look at the
structure of the mitochondria you can
see it has an outer membrane and then it
has this folded inner membrane called
the crista within the cristes folds
you'll have an inner space or
compartment called the matrix and this
is why I tend to prefer talking about
the krebs cycle as opposed to using one
of the other names because hmm let's see
the matrix ever seen that movie who
started it Keanu Reaves kr Krebs cycle
crab cycles using respiration it's one
of those little memory trick some
harmonics that'll help you recall which
of all the different cycles happens in
the matrix of the mitochondria versus
what happens in the chloroplast during
photosynthesis if we take a look at the
whole process of aerobic respiration
every step generates some ATP the
glycolysis takes in the glucose splits
it in half to form some pyruvate and
spits out a little bit of ATP as well as
a couple of these NADH
molecules the krebs cycle takes in those
pyruvates breaks it up spits out a
little bit more ATP and then sends off
the nadh and fadh2 which are high energy
electron carriers off two electron
transport system you'll see that the
krebs cycle is what's generating the
carbon dioxide that you breathe out
every time you break down your sugar and
then the electron transport system is
what generates the load of ATP that is
the purpose of the aerobic respiratory
process using the energy of those
high-energy electrons so let's take a
closer look at the Krebs cycle
now I've simplified a lot of the steps
because most teachers don't have you
memorize each and every molecules name
as you go through the process but in
general what happens is that pyruvate
from glycolysis out in the cytoplasm as
it starts to enter into the mitochondria
enzymes will rip off a couple of
high-energy electrons and put them onto
an electron carrier called NAD+ you add
two electrons it becomes negatively
charged and then grabs a nearby
positively charged hydrogen ion and
becomes NADH
so this NADH is a full high-energy
electron carrier full of high-energy
electrons and it goes off to the
electron transport system where those
high-energy electrons can be used to
generate a lot of ATP you have two
carbons left because one of the carbons
falls off when you pull off those
high-energy electrons a two-carbon group
is called an acetyl group you put it
onto this holder or helper molecule
called coenzyme a it's a coenzyme which
means it's not an enzyme but it helps
enzymes do their job so we call this
combination of two carbons plus coins ma
acetyl co a that two carbon acetyl group
joins to a four carbon molecule called
oxaloacetate right at the beginning of
the Krebs cycle
forming a six carbon molecule called
citric acid which is why this is
sometimes called the citric acid cycle
as that happens the coenzyme a it goes
back to pick up another two carbon group
from a broken-down pyruvate and it just
keeps going back and forth shuttling in
the two carbon groups that came Eltham
utley from the glucose that entered the
cell you pluck off a couple more carbon
dioxides and every time you do that you
pull out some high-energy electrons
putting them onto those high energy
carriers called NAD+ turning them into
nadh ultimately in one of these steps
you can make a little bit of ATP every
pyruvate that enters generates one ATP
so because every glucose six carbon
molecule creates two pyruvates you go
from one ATP group another ATP
ultimately you also wind up in this last
part where you're regenerating that four
carbon molecule that you began with
right here called oxaloacetate during
this regenerate Ori process you actually
do make some fadh2 from electron carry
called F ad now you'll wind up making a
lot more nadh than the fadh2 but don't
worry it's just a fad all right so
that's the krebs cycle pyruvate comes in
gets ripped apart
you put the high-energy electrons that
are helping hold the pyruvate together
onto our NAD+ making nadh a couple of
them go on to fadh2 and you make a
little bit of ATP