7.06 Cell Biology
^#

7.06 Cell Biology

Definitions
^#

Techniques
^#

1. Why is cell biology exciting? Questions and techniques
^#

@2022-09-07

2. Compartmentalization: the membrane system
^#

@2022-09-12

Readings
- Alberts/5e, Chapter 10

The lipid bilayer
^#

Phosphoglycerides, sphingolipids, and sterols are the major lipids in cell membranes
^#

phospholipids are the most abundant membrane lipids; composed phosphate with two hydrocarbon tails
- phosphoglycerides. subset of phospholipids that have a glycerol backbone
- sphingolipids. phospholipids built from a sphingosine backbone rather than a glycerol backbone
phosphotidylserine is the only phospholipid with a net negative charge at physiological pH.
glycolipids ( $\not \subset$ phospholipids). resemble sphingolipids but have sugars attached rather than phosphate-linked head groups
eukaryotic plasma membranes have lots of cholesterol; almost 1 molecule for every phospholipid molecule
- cholesterol orients itself so that its polar head is adjacent to polar heads of phospholipid neighbors.

Structure of four major phospholipids in mammalian plasma membranes. Also includes a structure of sphingosine (the backbone of sphingolipids $\subset$ phospholipids).

glycolipids — Structure of four major phospholipids in mammalian plasma membranes. Also includes a structure of sphingosine (the backbone of sphingolipids $\subset$ phospholipids).

Phospholipids spontaneously form bilayers
^#

hydrophobic molecules group together in aqueous solution because the process of forming organized cages around the hydrophobic molecules decreases entropy (increases free energy), so free-energy cost is minimized if the surface area is minimized (which is accomplished when the hydrophobic molecules are grouped).

The lipid bilayer is a two-dimensional fluid
^#

The fluidity of a lipid bilayer depends on its composition
^#

Despite their fluidity, lipid bilayers can form domains of different compositions
^#

Lipid droplets are surrounded by a phospholipid monolayer
^#

The asymmetry of the lipid bilayer is functionally important
^#

Glycolipids are found on the surface of all eukaryotic plasma membranes
^#

Membrane proteins
^#

Membrane proteins can be associated with the lipid bilayer in various ways
^#

Lipid anchors control the membrane localization of some signaling proteins
^#

In most transmembrane proteins, the polypeptide chain crosses the lipid bilayer in an $\alpha$ -helical conformation
^#

Transmembrane $\alpha$ -helices often interact with one another
^#

Some $\beta$ -barrels form large channels
^#

Many membrane proteins are glycosylated
^#

Membrane proteins can be solubilized and purified in detergerents
^#

Bacteriorhodopsin is a light-driven proton pump that traverses the lipid bilayer as seven $\alpha$ -helices
^#

Membrane proteins often function as large complexes
^#

Many membrane proteins diffuse in the plane of the membrane
^#

Cells can confine proteins and lipids to specific domains within a membrane
^#

The cortical cytoskeleton gives membranes mechanical strength and restricts membrane protein diffusion
^#

Membrane-bending proteins deform bilayers
^#

3. Getting molecules across membranes
^#

@2022-09-14