hi everyone and welcome to biology professor today we're going to be talking about flippases and
floppases so first take a look at this drawing that i have here we're going to be talking
about some enzymes flippases and floppases that catalyze transverse
movement or transverse transverse diffusion across the plasma membrane
so transverse diffusion what this means is moving phospholipids from one
side of the lipid bilayer to another side so if you look here we've got some
some enzymes we're going to be primarily talking about these two today but these are embedded in
the lipid bilayer remember by layer means two two layers or two leaflets or two faces
so we've got the face that's up here and the face that's down here
and so these flippases and floppases they catalyze the diffusion of phospholipids from one side of
the membrane to another so that's the transverse diffusion sometimes it's called like flip-flop
movement hence their names flippases and floppases why do they do this to maintain membrane asymmetry
now i have another video that goes into much much much more detail on membranes and how they
are asymmetric how the basically the side of the membrane that faces the outside of the cell has
different groups different concentrations or frequencies of phospholipids than the
cytoplasmic phase the face that would be like facing this the cytoplasm so
that membrane asymmetry is important to membrane function and these are the types of enzymes that
help to build and maintain that asymmetry so these enzymes flippases and floppases and also
scramblases which i'm going to have another video separate on scramblases these are transmembrane
lipid transporter proteins you can see in the name exactly what they are they are trans membrane
proteins they span a membrane and what they do they transport lipids they transport lipids
from one side to another side depending on what type they are now these may be highly specific
highly specific meaning that a given flippase or floppase may only um allow the transverse movement
of like one specific type of phospholipid or some flippases and floppases may transport multiple
phospholipid types so it just depends on which kind you're looking at mutations in these kinds
of transmembrane lipid transporter proteins are associated with various diseases i've listed some
here angelman syndrome tangier disease stargardt diseases are pretty pretty rare um but pretty
consequential if you happen to have one and they cause defects in the activity of these transporter
proteins so with that said let's now turn our focus to flippases and flaw faces like i said i'll
have another video on scramblases so don't forget to check that one out so let's talk first about
flippases i've drawn flippases in here over here in red so i'm going to switch to that color here
flippases are p4 atpases so they're part of this family of proteins they are powered by atp
hydrolysis and you can see that right here so atp has to be used has to be hydrolyzed that terminal
third phosphate group gets pulled off a bond is broken that releases energy and it's that
energy that the flippase uses to drive forward its process so that's the atp hydrolysis uh basically
the cell has to expend energy to get this these slip bases to work now movement this is the the
major kind of distinction between flippases and floppases is which direction they're moving things
so the flippases are moving phospholipids from the exoplasmic that is the outside
face of the membrane or leaflet of the membrane to the cytoplasmic face or the inside face and so
i'm going to draw that right here flippases they are going to move a phospholipid from the outside
to the inside so make sure you see the direction that this arrow is going
basically moving something from this side to this side and so i have some examples here
abc a4 moves phosphatidyl ethanolamine that's a specific kind of phospholipid
so it's going to move just that one so that's an example of one of these highly specific ones
another example APLT moves phosphatidylserine and phosphatidylenolamine if you're confused
by some of these abbreviations i'll put in the video description what they stand for
that's phosphatidylserine is the ps phosphatidyl ethanolamine is the pe so now let's switch over
to talking about flaw paces so flaw paces are in a different protein family in the abc transporter
family rather than the p4 atpase family uh i've got quite a lot of markers in my hands right now
hang on a sec let me put one down uh i'm gonna switch to talking about floppases using a green
marker floppases are also powered by atp hydrolysis so you can see again atp that
terminal phosphate is pulled off that bond is broken energy is released and you can understand
why this would be you're having maybe not you i should say the flippases and the floppases are
having to move these hydrophilic heads through the the very hydrophobic tails those fatty acid tails
to get them to the other side of the membrane so it makes sense that some atp would need to be used
now this movement for floppases is in the opposite direction of the flippases so where the flippases
move from the outside to the inside the floppases do the opposite they move phospholipids from the
cytoplasmic or like the inner leaflet facing the cytoplasm inside the cell to the exoplasmic face
so basically moving from the inside leaflet to the outside leaflet and so i will draw that over here
we're going in opposite direction now going from the inside to the outside so again the direction
that these phospholipids are moving is opposite between flippases and floppases
so i've got some examples here abc a1 is a floppase that moves phosphatidylserine
phosphatidylcholine single myelin and cholesterol so it's acting on a bunch of different ones
moving them again from the inside to the outside face another one that i think is
really interesting is msba it moves lipid a from the inside to the outside specifically in e coli
and why do i think that this is noteworthy i used the wrong color there were stuck with the
green uh white i think says noteworthy lipid a remember that is the hydrophobic anchor for l
p s or lipopolysaccharide right i'll write that here lipopolysaccharide
remember that is a major defining component of gram-negative cell walls if you want to learn more
about gram-positive cell walls and gram-negative cell walls i've got a really great video on that
that you should check out so now let's turn our attention for a minute to biogenic flippases
these are maybe a little bit of a misnomer because biogenic flippases are more like scramblases
really than other flippases but because they're called flippases i'm going to talk about them here
now scramblases we haven't talked too much about but squam laces they move things in
both directions so there's those arrows to show you movement in both directions and they're energy
independent meaning that no atp is required so biogenic flippases are similar again energy
independent so unlike regular flippases no atp hydrolysis is required these biogenic flow bases
are located in biogenic membranes what does that mean biogenic is referring to where the membranes
are primarily synthesized and so in prokaryotes this is going to be in the plasma membrane but in
eukaryotes like humans for example and eukaryotes these biogenic flow bases are going to be located
in the endoplasmic reticulum membrane so i'm going to abbreviate that er endoplasmic reticulum and in
the golgi apparatus membrane so i will abbreviate that ga so the goldie apparatus or multibody
the er and then in prokaryotes in the plasma membrane that's where the membranes are being
synthesized and that's where you have biogenic flippases working these are bi-directional
just like the scramblases they can go in either direction but the kind of major movement and i
think why these are generally considered flippases is because in general these uh lipids are being
synthesized um in eukaryotes in particular in the er lumen so that's like in the inside compartment
inside the endoplasmic reticulum and so they're having they're being made there and so the ones
that need to stay there can stay there but the ones that need to be moved into the cytosolic
side or the cytoplasmic side um they have to be moved and it's the biogenic flow bases that do
that movement remember that um other faces we're going from the outside to the cytoplasmic side
cytoplasmic and cytosolic are in interchangeable terms here but biogenic flippases also move lipids
primarily from in this case it's actually inside the ER but to the cytosolic site
so just like this right here with movement flippase movement to the cytoplasmic side
this right here is movement to the cytoplasmic side remember cytosol
is the aqueous component of cytoplasm that's why we can use them interchangeably here
and then we've got our major example of a flip of a biogenic flippases being the er
flippase remember er stands for endoplasmic reticulum i want to mention one other thing and
that's that occasionally you will hear flippases and floppases and biogenic flippases and sometimes
even scramblases all referred to as just flippases this is really not the most correct the
most correct is to to characterize them based on their energy usage and the direction of transport
to distinguish between flippases between flaw faces between scramblases but sometimes you will
hear just flippases kind of as a more generic term so don't forget to check out my other
videos like the one on scramblases and the one on membrane asymmetry and the one on gram positive
versus gram-negative cells let me know what you think in the comments below please subscribe
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so much for watching biology professor good luck with your studying and i will see you next time