Week 2: Membrane Structure and Proteins Flashcards
Membranes and proteins
what % of the lipid bilayer do proteins vs lipids make up?
on average 50/50
how wide is the lipid bilayer?
5 nm
which types of lipids are the most abundant in membranes? what about animal cell membranes?
phospholipids; phosphoglycerides (1), sphingolipids, and sterols
what type of phospholipid is phosphatidylserine? What type is sphingomyelin? what type is cholesterol?
a phosphoglyceride; a sphingolipid; a sterol
what bonds do hydrophilic molecules make?
hydrogen bonding
what is a micelle?
a cone shaped lipid bunch that has the hydrophobic tails on the inside and hydrophilic heads on the outside => spontaneously forms
whats the most energetically favorable arrangement for phospholipids?
a bilayer due to the cylindrical shape of their 2 fatty acid tails
what is a liposome?
a synthetic lipid bilayer made in a lab for experimental purposes that can be 25 nm to 1 micron in diameter
where does phospholipid synthesis take place?
the cytosolic monolayer of the ER where lipids are made
what does scamblase do?
non selectively equilibriates phospholipids between the 2 monolayers in the ER membrane to result in even growth
- flips from cytosolic side to lumen side
what factors affect bilayer fluidity?
temperature, fatty acid chain length, double bonds, cholesterol
lipid rafts
regions of a membrane enriched with sphingolipids, glycolipids, cholesterol, GPI anchored proteins, and some transmembrane proteins to form a micro domain of interactions
- patches of specialized structures and functions
what is a glycolipid?
when fatty acid tails are linked to a glycerol head that protrudes out of the bilayer => does not have a protein region
what is a glycoprotein?
a protein that has glycogen (sugar) on the head of its extracellular leaflet
what is a GPI anchored protein?
a peripheral protein linked to a GPI lipid anchored head in the extracellular leaflet
what is an oligosaccharide linker?
the sugar portion of the GPI linker between the lipid anchored part and the peripheral protein
what does seipin do?
its a transmembrane protein that associates with assembly factors to help produce a budding lipid droplet => assembly factor stays on the droplet with associated proteins and seipin stays in the membrane on the cytosolic side
what is phosphatidylserine?
a negatively charged molecule that stays on the inner cytosolic monolayer of the plasma membrane because it signals for apoptosis to macrophages
where are glycolipids found?
exclusively found in the non cytosolic monolayer
what does flippase do?
moves specific phospholipids from the outer monolayer to the inner monolayer in the plasma membrane
why is asymmetry lost in apoptotic cells?
inactivation of flippase for phosphatidylserine and activation of scrameblase which transfers random phospholipids in both directions between monolayers
what are gangliosides?
glycolipids containg one or more sialic residues (causes negative charge)
what are functions of glycolipids?
protection of the membrane, cell recogntion and adhesion, sugar modification recognized by receptors, receptors for pathogens, etc.
membrane protein classifications
transmembrane proteins that span the membrane or one leaflet, lipid linked proteins which attach to lipid anchors in the bilayer, peripheral proteins which noncovalently bind to transmembrane proteins
hydrophobic residue
non-polar side chains
glycophorin
determines ABO blood types in RBC’s as a membrane spanning protein
bacteriorhodopsin
has several membrane spanning domains and acts as a proton pump through light energy
hydropathy plots
allow us to see transsmembrane amino acid sequences because they reach up to 1 on the graph
beta barrel proteins
multiple membrane spanning strands of a polypeptide that form a sheet rolled up into a cylinder
pourin
water filled channel made from a beta barrel protein in the plasma membrane
where do lipid linked proteins attach? Examples?
some link to fatty acid chains, myristoyl, palmitoyl, prenyl groups associated in the cytoplasmic monolayer of the plasma membrane
what does a GPI anchor do?
attaches to a peripheral membrane protein on the non cytoplasmic monolayer
what is a signal switch?
occurs when modifications of a signal (usually extracellular) are reversed
what are oligosaccharide chains?
found on glycosylated proteins on the extracellular side of the plasma membrane always
disulfide bonds and where do they occur?
on the extracellular domains of proteins where cysteine amino acids have a S that attaches together
- this doesnt happen on the cytosolic side because of the reducing environment
glycocalyx
the carbohydrate rich zone on the surface of cells coated in sugars
what contributes to the glycocalyx
glycoproteins, glycolipids, proteoglycans a type of glycoproteins, extracellular matrics adsorbed on the cell surface
functions of the glycocalyx
protection, maintaining intercellular distances, cell recognition/adhesion
what must you add for membrane proteins before isolation?
solubilization
how do you isolate peripheral proteins
gentle extraction like high salt buffer, or altered pH
how do you isolate GPI linked proteins
through the enzyme PI-PLC which digests the structure so the proteins can be released from the extracellular side (cleaves lipid anchor)
what are detergents?
amphiphilic molecules that displace the phopholipids in the bilayer and isolate transmembrane proteins
what was the cell called that fused mouse and human cells? what purpose did that serve?
heterocaryon; lateral diffusion of proteins
what is FRAP?
fluorescent recovery after photobleaching => tells us how much/fast proteins diffuse in a membrane and if they may be restricted
formation of membrane domains are from which 4 cases?
lipid rafts, interaction with the extracellular matrix, interaction with cell-cell adhesion, interaction with cytoskeleton
what are the cytoskeletal networks made up of?
actin filaments bind the network together on the cytosolic leaflet of the plasma membrane
what is a corral?
a domain enclosed by the cytoskeletal network that restricts lateral movements of membrane proteins
what tracks protein diffusion via microscopy?
Signal particle tracking to define membrane domains
