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