Lecture 3 Summary Made the lecture notes more readable.

44 views14 pages
user avatar
Published on 16 Oct 2011
School
UBC
Department
Biology
Course
BIOL 331
Professor
Page:
of 14
Chapter 10 The Lipid Bilayer and Membrane Proteins
From the previous lecture...
FRET
- Protein-protein interactions are key to understanding how cells work
- Co-localization of suspected protein partners using immunofluorescence microscopy in fixed
cells is possible and popular
- Bu the resolution of the fluorescence microscope is much less than the size of a typical protein,
co-localization is often a questionable result
- FRET allows direct observation of molecular interactions (2-5 nm) in living cells
The Plasma Membrane is Crucial to Cellular Life
- The cell membrane separates the cell from its environment and creates intracellular
compartments (in eukaryotes)
- Ion gradients across the membrane are used to make ATP, to allow electrical signals in nerve
and muscle cells and to drive transmembrane movement of solutes
- All biological membranes have a common structure: a thin layer of lipid molecules with proteins
held together by non-covalent interactions
- Membranes are fluid, dynamic structures
- Lipids found as a bilayer are about 5 nm thick
- The lipid bilayer is impermeable to most water soluble molecules
- Transmembrane proteins
A) Transport specific molecules across the membrane
B) Catalyze membrane associated reactions (ATP synthesis)
C) Are structural links or cell surface receptors
- An estimated 30% of all proteins in the genome are membrane proteins
The Lipid Bilayer
- The lipid bilayer forms the basic structure of all
biological membranes
- Lipid bilayer is easily seen by TEM
- Structure of the lipid bilayer is inherent to the
properties of lipid molecules
- Lipid molecules will assemble spontaneously to form
lipid bilayers under simple artificial conditions
- Animal cell membranes by mass are half lipid/half
protein
- All lipid molecules in cell membranes are amphipathic (a hydrophobic tail and a hydrophilic
head)
- Most abundant membrane lipids are the phospholipids (a polar head
group and two hydrocarbon tails usually fatty acids 12-24 C atoms)
- One of the two tails is usually saturated, the other usually one or
more cis C=C bonds
- The main phospholipids are the phosphoglycerides (3C glycerol
backbone)
The Phosphoglycerides
E.g. phosphatidylcholine
- The four major phospholipids are half of all the membrane lipids by mass
Note: Phosphatidylserine carries a net negative charge
Cholesterol
- Also an important part of the lipid bilayer
Lipid Shape and Amphiphilic Nature
- Spontaneous assembly of bilayers or micelles
- Free edge with water is energetically unfavourable
Lipid Bilayer A 2D Fluid
- Synthetic lipid bilayers (spheres 25 nm 1 μm) liposomes, bilayers
- Each side of a bilayer is sometimes called a leaflet
- Motion of phospholipids can be measured in artificial membranes (by fluorescent labelling or by
electron spin resonance)
A) Lateral diffusion is extremely rapid (length of a bacterial cell in 1 s!)
B) Flip flop (one leaflet to the other) is extremely rare
C) Rapid rotation along long axis, flexible tails, a disordered system

Document Summary

Chapter 10 the lipid bilayer and membrane proteins. Protein-protein interactions are key to understanding how cells work. Co-localization of suspected protein partners using immunofluorescence microscopy in fixed cells is possible and popular. Bu the resolution of the fluorescence microscope is much less than the size of a typical protein, co-localization is often a questionable result. Fret allows direct observation of molecular interactions (2-5 nm) in living cells. The plasma membrane is crucial to cellular life. The cell membrane separates the cell from its environment and creates intracellular compartments (in eukaryotes) Ion gradients across the membrane are used to make atp, to allow electrical signals in nerve and muscle cells and to drive transmembrane movement of solutes. All biological membranes have a common structure: a thin layer of lipid molecules with proteins held together by non-covalent interactions. Lipids found as a bilayer are about 5 nm thick. The lipid bilayer is impermeable to most water soluble molecules.