Question

Cell Biology Tutorial: Structure, Composition, & Organization of the Lipid Membrane

Answer 1

Note: This is a reference for educational/studying purposes, not a question, please save all comments or questions for the end.

Answer 2

\({\bf{Basic~Structures}}\)
- micelles (rarely formed unless chains are removed)
- liposomes
- phospholipid bilayer (most common, spontaneously formed to minimize contact of hydrophobic chains with water; stabilized by van der Waals between tails)

type of structure depends on: added proteins, length of chains, degree of saturation, temperature

some organelles (nucleus, mitochondrion, chloroplasts) have double membrane; endosymbiont hypothesis

\({\bf{Characteristics~of~Membranes}}\)
1. impermeable to water-soluble membranes
2. stability by hydrphobic interactions
3. form sealed enviornment that is distinct from the exterior

internal face: cystolic
external face: exoplasmic
lumen of a vesicle, when formed, is chemically equivalent to the extracellular space when it "pinches" in

some can have projections like cilium and flagella for movement or surface area extension

\({\bf{Classifying~Lipids}}\)
- phosphoglycerides
- sphingolipids
- sterols

\({\bf{Phosphoglycerides}}\)
- derived from glycerol 3-phosphate
- hydrophobic tail + two fatty acid chains esterified to two hydroxyl groups in glycerol
- characterized by head group type and charge
- subgroups: phosphoinositides, lysophospholipids, plasmalogens

\({\bf{Sphingolipids}}\)
- derived from sphingosine, amino alcohol w/ long chain and fatty acid attached to sphingosine
- most commonly found in nervous tissue
- subgroups: sphingomyelin, glycolipids

\({\bf{Sterols}}\)
- 4 isoprenoid ring structure
- cannot form membranes on their own
- confer stability to membranes in high concentrations but also allow fluidity
- most common ex: cholesterol

Answer 3

\({\bf{Mobility}}\)

- high lateral mobility between lipid molecules
- diffusion rate sensitive to temperature
- overall viscosity similar to that of olive oil
- do not spontaneously move from one side of the membrane to the other, must have flippase to do this
- protein-rich regions and cholesterol restrict movement
- some lipids are bound to integral proteins and have restricted movement

\({\bf{Membrane~Properties}}\)

- ex. sphingolipids: increased stability due to hydrogen bonding, higher conc. in golgi membranes
- shorter acyl chains = increased fluidity
- curvatire determined by shape of the lipids; cylindrical = flat membrane, cone = curved membrane
- composition: generally asymmetric about both sides of the membrane
- relative abundances determined by phospholipase hydrolysis

\({\bf{Membrane~Microdomains}}\)
- lipid rafts: formed by cholesterol and sphingomyelin, can be disrupted with methyl-beta-cyclodextrin
- lipid droplets: vesicular structures composed of tryglycerides/cholesterol esters, function as lipid storage or sites for proteins slated for degradation, grow by adding lipids until the droplet leaves the ER

Answer 4

This is the end of my tutorial; I hope you found it helpful.

If you have any ∗relevant∗ comments or questions I will attempt

to address them to the best of my ability.

Thank you for reading!