Lipid membranes Flashcards
Function on membranes
barrier accumulate nutrients energy transduction facilitate cell motion assist in reproduction modulate signal transduction mediate cell cell interactions
Lipid bilayers can form in various ways
unilamella vesicles (liposomes) multilamellar vesicles
Fatty Acids form clusters when they react with
cations
Mark Bretcher showed that
N-terminus of glycophorin is extracellular
C -terminus is intracellular
Flippases vs floppases
Flip-in to out
Flop -out to in
Types of membrane proteins
integral
peripheral
lipid anchored
Peripheral proteins can be dissociated from the. membrane , how?
With Salt solutions, or changed in pH
Intergral membrane proteins can be removed from the protein , how ?
detergents or organic solvents
Examples of integral membrane proteins
bacteriorhodopsin and glycophorin
Glycophorin is a
single transmembrane segment protein
Acts as a grease
regarding glycophorin , N and C termini face which direction
N-extracellular
C-cytosol
A 7 transmembrane protein
Bacteriorhodopsin
Found in Gram negative bacteria and in mitochondria outer membrane
Porins
Structure of a porin
Beta sheet closes to form beta barrel which is hydrophilic on the inside.
Four types of Lipid Anchored Membrane Proteins
- Amide linked myristoyl anchors
- Thioester linked fatty acyl anchors
- Thioether linked prenyl anchors
- Glycosyl phosphatidylinositol anchors
A common anchoring protein is
N-myristoyl anchoring motif
N-myristoylation always occurs at
An N-terminal glycine residue
Examples of Myristoyly anchors .. what the main point
Not always attached to a membrane
Palmitoylation always occurs where?
Cystein residues in the C terminal
Amide linked Myristoyl anchors
Myristic acid
Thioester linked Acyl Anchors
palmitate is most common , myristate, strearate, oleate are also all found.
Proteins containing the C-terminal sequence , CAAX can undergo
prenylation reactions that put either geranylgeranyl or faresyl groups at the cystein side chain
Prenylation is accompanied by the
removal of the AAX peptide bond and methylation of the carboxyl group of the cysteine residue , which has become the C-terminal residues.
Most elaborate anchors
Glycosyl Phosphatidylinositol Anchors
examples are surface antigens, adhesion molecules, cell surface hydrolases
Glycosyl Phosphatidylinositol Anchors are alway attached at ?
C-terminal residue
Core of glycosyl phosphatidylinositol anchors
three mannose , and a glucosamine