Cell
Lecture 2
Membrane Structure
Lipids
Membrane Proteins
Three major types
Phospholipids
Glycolipids
Sterols
Most common, one saturated and one unsaturated tail, glycerol or spingosine backbone, negtively charged or neutral, found on both leaflets
Can be used for Signaling
PI and PtdIns
Less common, two saturated tails, negatively or neutral charged heads, sphingosine bb, extracellular leaflet
Abundant, one tail, bulky bb, small polar head group, found on both leaflets
Functions
Non-Structural Aspect
Regulates membrane
Protein activity
Dependant on Calcium ion
concentration being low in cytosol
Lipid Rafts
Glycolipids/Cholesterol
Transmembrane proteins
preferentially enriched
Glycolipids can be
recognized by lectins
Biosynthetic precursors to
signaling molecules
General fxns
Less than 1% of PM
Cytosolic leaflet
Two main types of proteins
Clathrin mediated the internalization process, recognizes PI(4,5)P2
Ligand binds to
extracellular surface
PLC activation
Cleave PIP into DAG and IP3.
The latter being soluble
Beta Strands
Alpha Helix
Stability comes from the hydreogen bond from
c=o and the N-H of a neighboring strand
Stability comes from the hydreogen bond from
c=o and the N-H of the same chain
Sugar modifications are common forming glycoproteins in the extracellular/lumenal side
Lipid anchored proteins
Integral membrane proteins
First Synthesized
in the ER
A GPI anchor is attached to C-terminus
Lipid anchor resids on lumenal/extracellular leaflet
Peripheral Membrane proteins
Can be extracellular or lumenal
associated with other proteins via
hydrophilic intx
lecture 4
Intracellular Compartments and Protein Sorting