BIOL 2021 Lecture Notes - Glycosylphosphatidylinositol, Lipid Bilayer, Membrane Protein

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Published on 16 Oct 2011
School
York University
Department
Biology
Course
BIOL 2021
Professor
Biol 2021 March 12 2009- lecture- Chapter 10
Proteins in membrane
Membrane proteins perform most of the membranes specific tasks and therefore give each type
of cell membrane its characteristic functional properties.
Amounts of protein vary according to membrane function as well
Typical plasma membrane has amount half its mass as protein
Types of membrane proteins
Membrane association with proteins 2 classes:
I. Intergral
- Mainly defined by “cannot be washed off with high salt soltutions; membrane must be
disrupted with detergent in order to be accessed and purified
- Protein that is retained in a membrane by virtue of one or more domains that span or
are embedded in the lipid bilayer
- Inside membrane, integrated tightly
- Transmembrane proteins and many proteins held
in the bilayer by lipid groups or hydrophobic
polypeptide regions that insert into the
hydrophobic core of the lipid bilayer
- Single pass transmembrane protein: polypeptide
chain crosses only once
- Multipass transmembrane proteins: polypeptide
chain crosses multiple times
Peptide chain can form B barrel (b sheet rolled into barrel) ie. In porin
proteins
a. -(1,2,3): transmembrane proteins: proteins that extend through the lipid bilayer with part of
their mass on either side
Amphiphilic, with hydrophobic regions that pass through the membrane and interact with the
hydrophobic tails of lipid molecules in the interior of the bilayer where they are sequestered
away from water. Also has hydrophilic region exposed to water on either side of the membrane
The covalent attachment of a fatty acid chain that inserts into the cytosolic monolayer of the
lipid bilayer increasesthe hydrophobicity of some of these transmembrane proteins (ie, protein
1. In figure)
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- Protein #1: single alpha helix, transmembrane; covalently attached fatty acid chain
inserted in the cytosolic lipid monolayer
- Protein #2: multiple alpha helix- multipass transmembrane protein
- Protein #3: B sheet- beta barrel
- Protein #4: Alpha helix on cytosolic monolayer by amphiphilic alpha helix
- Protein #5: associated with cytosolic side by covalently attached lipid (that anchors it to
cytosolic monolayer and keeps it in place)
- Glycossylphosphatidylinositol (GPI) anchor
Anchor protein to membrane by glycosyl linkage
Found in signalling
Protein can be released with enzyme called phosphatidlinositol-specific
phospholipase C, which cuts proteins free from their anchors
- Protein #6: covalently attached via ogliosaccharide linker to phosphatidylinositol in the
non cytosolic monolayer (GPI anchor)
- ALPHA HELIX
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Document Summary

Biol 2021 march 12 2009- lecture- chapter 10. Membrane proteins perform most of the membranes specific tasks and therefore give each type of cell membrane its characteristic functional properties. Amounts of protein vary according to membrane function as well. Typical plasma membrane has amount half its mass as protein. Mainly defined by cannot be washed off with high salt soltutions ; membrane must be disrupted with detergent in order to be accessed and purified. Protein that is retained in a membrane by virtue of one or more domains that span or are embedded in the lipid bilayer. Transmembrane proteins and many proteins held in the bilayer by lipid groups or hydrophobic polypeptide regions that insert into the hydrophobic core of the lipid bilayer. Single pass transmembrane protein: polypeptide chain crosses only once. Multipass transmembrane proteins: polypeptide chain crosses multiple times. Peptide chain can form b barrel (b sheet rolled into barrel) ie. in porin proteins.