Lecture 4 Flashcards
Hereditary Spherocytosis
genetic disorder + type of hemolytic anemia
(rupture of RBC)
RBC lose biconcave flexible shape + become spherical (can’t pass through narrow caps)
proteins att ing cell mb to cytoskeleton are not working
symptoms/physcial reps
fatigue
dizziness
hair loss
eye yellowing
cell mb structire
supported by__
a meshwork of proteins called cell cortex
mb is a thin fatty film s proteins and coated w carbs
carbs att plasma mb proteins and lipids on outside of mb form a sugar coating = glycocalyx
glycocalyx
sugar coating formed by
the carbs att to plasma mb proteins and lipids on outside of mb
cell cortex
actin
myosin
acting binding proteins
= spectrin in RBC
= anjyrin in RBC
plasma mb
lipid bilayer
lipids in plasma mb
are phospholipids, cholesterol and glycolipids
all are amphipathic = have hydrophilic head and hydrophobic tail
phosphatidylcholine
ex. of phospholipidmost common phospholipid in biological mbs
structure of phosphatidylocholine
hydrophilic head = choline molecule and a phosphate group
glycerol links hydrophilic head and hydrophobic tails
tails = 2 fatty acid chains
tails in a phospholipid can be __ or ___
saturated = no double bonds, C bound to max # of H has they can
or
unsaturated = w double bonds bn C atoms, so still could add H
hydrophobic vs hydrophilic interactions w env
hydrophilic heads face water on both sides of bulayer
hydrophobic tails are shielded from water and lie next to one another in the interior
phospholipid bilayers from sealed compartments
a flat sheet of phospholipid bilayer is energetically unfavroable, since the hydrophilic tails are exposed to water along its edges, like the filling of an Oreo
so spont close on themselves to from sealed compartments
closed = stable bc h phobic tails are sheltered from water
layer facing cytosol = cytosolic monolayer/face
layer facing exterior of cell = non-cytosolic monolayer
bilayer is a flexible 2D fluid
plasma mb is flexible and components can move freely w/in the layer
movements of a single lipid in a mb
rotate, move laterally, flex of tails (spread them apart, little hoe) or flip to the other layer
factors effecting the fluidity of the plasma mb
- temp, inc temp = inc fluidity
- lipid composition, dec cholesterol = inc fluidity
cholesterol= fills gaps = limtes movements = stiffen plasma mb = more rigid
- tail saturation
unsaturated hydrocarbons = more fluid
double bond = kink/bend in tail = more movement bc more room provided
sat = no double bond, tails stay straight, are pushed together tightly
- tail length
shorter fatty acids = more fluid
since more space to move
new mb is made in SER
a glycerol phosphate cmpd and a fatty acid chain are grabbed and condenses it to one structure by a first enzyme
a phosphate grp is removed
a choline grp is added
made and incorporated into cytosolic face of SER plasma mb
after phospholipids are synthesized, they’re added to cytosolic face of bilayer…..
but uneven distribution so SCRAMBLASE catalyzes the random transfer of phospholipids from one monolayer to another
now, there is a symmetric growth of both halves of bilayer
new mb is then matured in Golgi mb
new plasma mb is delivered to the Golgi plasma mb through vesicles
in Golgi, specific p lipids are transferred back to cytosolic monolayer, w FLIPPASE that catalyzes the transfer of certain ones
now asymmetrical = each layer has diff types of phospholipids + uneven #’s
plasma mb asymm is preserved during mb trasnfer
plasma mb is transported by porcess of vesicle budding from Golgi and fusion w the cell mb or mb of other organelles
mb retain orientation during transfer bn cell compartments
lipids in cytosolic monolayer always face the cytosol
plasma mb protein fns
transporters
ion channels
anchors
receptors
enzymes
2 general types of mb proteins
internal -
1. trans mb proteins, = go through entirety of mb
monolayer associated = only assoc w one side, doesn’t go all the way through
lipid linked (anchored) = directly linked q phLi in mb
peripheral
protein attached or lipid attached
trans mb proteins usually cross lipid bilayer as alpha helix
single pass trans mb proteins have a hydrophobic region that is inserted w/in mb, what interacts w h phobic tails, h philic side chains exposed to aqueous env
aa of a mb protein are localized depending on polarity
non polar = h phobic = assoc directly w h phobic
polar = h philic = assoc w internal and external faces
so outer circle is non polar bc int w tails, h phobic
inner circle is polar, int w polar substances passing through + env
so have amphipathic alpha helices (like mb, has h phobic + h philic)
movement of proteins in lipid bilayer
if fuse mouse and human cells together + dye each cells proteins separate colours, when first fused is a strict separation, then will start to intermix
movement of proteins can be limited
can stop moving and keep at one location by
1. binding to cell cortex, inner network of cell supporting shape of cell
- by binding to extracellular matrix molecules
- by binding proteins on other cell surface
- by adding junctions/barreirs to restrict
ex. tight jns in gut, stop acid from reaching epi of gut
glycocalyx recap + role
sugar coating made by carbs added to proteins and lipids on the outside face of the cell
sugars re added in ER of golgi
carbs on glycoprotein and proteoglycans involved in cell/cell recog and adhesion
fns of cell mb
cell signaling
transport (w channels)
cell growth/motility
cell/cell recognition
intercellular adhesion
