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1- 32 Membrane Structure Ch10 (18- Oct) (2- cell membrane or membranes…
1- 32 Membrane Structure Ch10 (18- Oct)
1- extra cellular portion
white area outside:
usually taken by extra cellular matrix
fibre actin, collogen
different membrane
mitochondria
mitochondria membrane
nucleus
nuclear envelop
differences:
pores in the nuclear envelop for proteins to go in (they will be produduced out of the nucleus) and RNA to go out of the nucleus
how large are nuclear envelop pores>>> large enough for proteins to go in and out
2- cell membrane or membranes within a cell are selectively permeable
less particles on the left hand side : hypotonic
more particles on the right hand side : hypertonic
if we didn't have this selectively permeable membrane in the middle
particles would move and find equi
if selectively permeable memb. in the middle
the particles can not move throu
to make the tonicity the same water should move from left to right to make the tonicity the same
concentration of Na and K
to generate action potentials in neurone
infornation barrier: if you dont have any barrier between outer wall to the inside wall>>> you can not select the information you want
there will be a lot of receptors and ligands and enzymes
located in the cell membrane
which will recieve a signal and translate the signal
to be able to use within the cell
transportortation of small molec.
ion channels, K and Ca channels
capacity for movememnt and expansion
scratch on the skin
cells migrate and close the gap
to maintain a cell as an entity cell membrane has to be felxible to move not a fixed shape cubic moving around
3- plasma membrane= cell membrane= cellular membrane = plasma membrane
double layer= bilayer
first building block is a lipid portion in red
the other big building block is the proteins in green
this is an electro micrograph of red blood cells : YOU CAN SEE DOUBLE LINES AT CELL MEMBRANE
actual length of lipid bilayer = 5 nm
including all proteins becomes around 10 nm
4-premitive imaging tool= freeze fracture
how do we actually know how the lipid bilayer would look like
we freez cells into lipid nitrogen, will freez instantly
put sharp knife to cut the bilayer
look at the inside of the extracellular layer and inside of the cytoplasmic layer
what you see is not symmetric
because protein is not totally always embeded in the double layer
or when you cut out they attach to one layer than the other
5- building blocks
building block no 1: phospholipid
amphipathic
a molecule which is hydrophilic as well as hydrophobic
Glycerol has 3 connections
connection towards up: hydrophilic head group which is polarized: so there will be negative charge usually
through the phosphate is cholin
towards the buttom
2 connections to the fatty acid tails
a cis double bond on the second fatty acid tail
Hydrophilic vs. hydrophobic in water
acetone is water friendly
when we put this acetone in water
tries to connect through hydrogen bond
stable status
dont have any problem having acetone in the water
hydrophibic can not make any hydrogen bond
methylpropane goes into the water
water molecules avoid that very hydrophobic molecule
hydrophilic tries to make the surface area towards the hydrophobic minimum because that is energetically stabler
has a hydrophilic and hydrophobic portion
it is like cone shape and multiple of them in water is like ball shape
hiding all hydrophobic tail twards middle
exposing all hydrophilic heads twards the water
sphere shape
all hydrophilic will touch the water and all hydrophobic will touch eachother not exposed to the water
energetically it is stabel
phospholipid: more of cylinder shape rather than cone
make a bilayer sheet exposing hydrophilic heads twards the top or buttom and hiding all the hydrophobic portions to the middle
bilayer sheet is not very stable because you see a lot of exposed hydrophobic areas to the water
they can wrap around and make a hallow sphere so they can only expose hydrophilic portion twards water and having little bit of water within sphere but nor touching the hydrophobic portion becaouse still another layer of hydrophilic heads
that is something called liposome :star:
when we want to insert water soluble drug into the cell
we need to encapsulate water soluble drugs within enclosed water if those drugs are small enough to go to the cell membrane
1 more item...
we put it inside the water and liposome will go and merge with membrame then the enclosed drop will get into the cell
1 more item...
4 major phospho lipids we find at animals cell membrane
familiarize yourself with the names
6- computer simulation in pico second scale they form bilayer which is another evidence that this is enegetically favourable
they found that phospholipid can move around>>> also rotate and flex also do flip flop changing the location from top to buttom very rare= flexibility of cell membrame = flexflip
FRAP- another evidence showing phospholipid can move around is through FRAP= Fluorescence recovery after photo bleaching
florescent colour agent >>> we use them to colour proteins in the cells - we can see and visualise where they are and how much they express
tag coulours with cancer tagging molecules and surgeon spray molecules with cancer tagging on to those tissues and shine the correct wave length to visualise it very shortly and take tumor tissue out and put it on to different stand
shine the wavelength again to make sure the sugeon did not take the nerve >>> may be too late but better to not knowing at all
you shine with strong laser burning florecent molecules
so you dont see any colours coming up from florecent microscope
if the phospholipid doesnt move you should keep seeing black area instead of green florecent
in reality phopholipids move around even during photo bleaching there is movement
they call it recovery bot actually they dont recover those signals >>> they difuse into there is a little bit of recovery of signal to 70% the green florecent will come back
after a short time period you scan the photo bleached area and you see some green florecent coming through
Protein diffusion in plasma membrane
another evidence: they made a hybrid cell of mouse and a human
label mouse cell with green and human cell with red and they fuse them into single cell
they shoud see mouse cell on the top and human at the buttom
but they saw green colour all throughout the cell and red colour all throughout the cell
membrane transfer during myotube fusion
we had fatty tail with colouring agent
stem cell from human fat
half labled with green theother half with red
stick it around on the plastic or hydrogel
they form to a double nucleated myotube which is a building block for muscle and having both green and red
meaning : when they fuse one green one red into one cell dont have green on the left vs red on the right
phospholipid diffuse around you get signal throughaout the cell
7- cholesterol in lipid bilayer
cholestrol= very small polar head and very large hydrophobic
cholestrol can be amphipathic as well as phosphilipid
can fit perfectly between 2 phospholipids
computer simulation
when we have only phospholipid without cholestrol it could be quite tight and quite leaky :question:
water molecules literally leak to the hydrophibic area
as soon as you add cholestrol that doesnt happen
but when we have not bended fatty acid >>> 2 straight fatty acid as a tail it could be quite thick and quite packed there wount be any leak >>> the problem is that they wount be as flexible becaouse they dont have any space to play around
by adding cholestrol what we can achieve is a good thing between those 2
make membrane not as leaky while maintaining the flexibility
8- glycolipids in plasma membrane
lipid chains with glyco : sugar rings
if you add glyco lipid as well as phospholipid then you see heterogineaty of the cell membrane , this can be very different from cell to cell (skin to cardiac to ... cells)
in the table fluidity depends on its composition
bacteria doesn't have cholesterol because they want to be more protective becau. they are exposed to the outer word rather than animal cells exposed to the extracellular matrix
9- phase seperation
when we mix 2 types of phospholipid to make a liposome and only one phospholipid was labled as red >>> you see very evenly distributed phospholipid
as soon as we add cholestrol on to those 2 different phospholipid
you see these type of patches
dont know why by cholestrol make phospholipids make some patches
we add another building block which is protein in green as proteins serve as channels or receptors so it is better for them to stay around rather than being apart
LIPID RAFT :star: cholesterol together with the proteins will make sth like a patch type >>> the patch is floating around rather than every single phospholipid and protein and cholesterol floating around as a chaos>>> we call those big patches raft because they float around as a group
10 Various ways of membrane proteins association
different types of protein we can find in memb.
1- aalpha halix going through the bilayer
2- groups of alfa halices
3- betasheet making a barrel : usually the inner spaces are larger so they serve as pores
4- alpha halix going just in one side of the lipid layer and having some intra cellular portions
5- protein can connect to the lipid chaine wich will anchor into the bylayer
6- thwards the outside a lipid can also connect to the protein thru the suger rings >>> that would be a glyco protein with some lipid domains
some proteins dont directly work with a membrane they work with a protein which is transmembrane protein
11- alfa-helical conformation of transmembrane proteins
hydropathy plot : is not the absolute amount of howmany hydrophobic molec. vs hydro philic . it is very relative changes per solution
when you put poly amino acid into solution they change their hydropathey
we put them in the water to see how hydrophobic vs hydrophobic it is
in pic yellow and green are hydrophobic
we see alot of hydrophobic amino acids rather than hydrophylic >>> so they can go better to the hydrophobic portion of the membrane
in hydropathy plot dark green are positive means they are hydrophobic in the water
the other protein bacteriorodopsin
have 7 portions of transmembrane alpha helices and all of them show top green which is positive value in hydropathy
Transmembrane a helices interact with one another
when they are made from RNA they are not necessarily bind together but as time goes by as the cell membrane is fluidity and flexible , protein will gather to gether for a better function