Membrane Structure and Dynamics Flashcards
list 3 ways in which membrane proteins associate with the lipid bilayer
- integral membrane proteins: consists of and alpha helix or a B barrel
- lipid-linked proteins: have covalently attached prenyl group, fatty acyl group
- peripheral membrane proteins: interact noncovalently with proteins/lipids at the membrane surface
are lipids distributed evenly across a membrane?
no, they may form rafts
what does the secretory pathway discuss?
the transmembrane passage of membrane and secreted proteins
- bring membranes together and help mediate vesicle fusion
SNARE’s
what is a micelle
aggregate of single tailed lipids
how are micelles formed?
it is driven by hydrophobic effect - water minimizes its contacts with hydrophobic molecules.
what are liposomes
a suspension of phospholipids can form liposomes, their diameters depend on lipid composition, solvent used and mechanical extrusion
explain phase transition in lipid bilayer
the transition temp. increases with the chain lenght, and degree of saturation.
- above the transition temperature its in liquid crystal phase
- below temp. its in gel-like solid phase
give 3 functions of membrane proteins
- catalyse chemical reactions
- transporters
- receptors
integral proteins are - oriented
asymmetrically
what is the secondary structure of the transmembrane segments
- for a polypeptide chain to penetrate the lipid bilayer it must have hydrophobic side chains to contact the lipid tails
- this requirement is met by formation of secondary structures that satisfy the H bond capacity of the polypeptide backbone
name the transmembrane proteins that contain alpha helices
- halobacterium salinarum bacteriorhodopsin
name the transmembrane proteins that contain beta sheets
E. coli OmpF porin.
an antiparallel sheet rolls to form a barrel. The number of B strands must be even.
Happen in porins
what is the most common prenylation site (occurs in lipid linked proteins)
c terminal sequence whit Cysteine and an aliphatic aa, and a residue Y which : if Ala, Met, Ser is faresylated. Or if Leu is geranylated.
In both its a thioether bond
what are the 2 kinds of fatty acids linked to membrane proteins
- mysristic acid: attached via amide linkage to N terminal Gly
- palmitic acid: linked via thioester bond with Cys
myristolation
is stable, and these proteins are ubiquitous
palmitoylation:
is dynamic, can be removed by palmitoyl thioesterases. Are found on cytoplasmic side of plasma membrane - where they participate in signaling
what is the role of spectrin
accounts for 75%of the erythrocyte membrane skeleton
- folds into triple stranded alpha helical coiled coils
what is the role of ankyrin
associates with spectrin, and ion channels + integral membrane proteins.
- provides attachment sites to anchor membrane skeleton to membrane
- right handed helical stack, with concave surface
where are membrane lipids synthesized
- SER
- in prokaryotes (the cytoplasmic face of plasma membrane
- in all cells, new membranes are generated by the expansion of existing ones
flappases
cause flip flop of specific phospholipids. Uses facilitated diffusion
phospholipid translocases
transport specific phospholipids across a bilayer using active transport
translocon
helps signal peptide cross the membrane
clathrin coated vesicles
transport transmembrane, GPI linked and secreted proteins from the golgi to the plasma membrane
COP1 coated vesicles
Carry out both the anterograde and retrograde transport of proteins between successive Golgi compartments. Also, they return escaped ER-resident proteins from the Golgi back to the ER. The COPI protomer contains seven different subunits.
COPii coated vesicles
Transport proteins from the ER to the Golgi. COPII vesicles components are then returned to the ER by COPI-coated vesicles. The COPII protein is made of two heterodimers
purpose of mannose 6 phosphate
is a lysosome targeting signal
purpose of Cterminal sequences, COPI, COPII
are ER targeting signals
