8.2 Membrane Components [HY] Flashcards
What is cell membrane predominantly composed of?
- lipids with some associated proteins and carbohydrates
- a large number of phospholipids with very few free fatty acids
What provides membrane structural integrity?
steroid molecules and cholesterol, which lend fluidity to the membrane, and waxes, which provide membrane stability
Triacylglycerols (triglycerides)
- storage lipids involved in human metabolic
processes. They contain three fatty acid chains esterified to a glycerol molecule. - Fatty acid chains can be saturated or unsaturated.
How are most fatty acids in the body made?
- Humans can only synthesize a few of the unsaturated fatty acids; the rest come from essential fatty acids in the diet that are transported as triacylglycerols from the intestine inside chylomicrons.
What happens when saturated fatty acids are incorporated into phospholipid membrane?
- saturated fatty acids decrease the overall membrane fluidity
Glycerophospholipid
- Formed by substituting one of the fatty acid chains of triacylglycerol with a phosphate group, a polar head group joins the nonpolar tails
- Commonly called phospholipid
- Phospholipids spontaneously assemble into micelles (small monolayer vesicles) or liposomes (bilayered vesicles) due to hydrophobic interactions.
Functions of phospholipids
- serve as second messengers in signal transduction. The phosphate group also provides an attachment point for water-soluble groups, such as choline (phosphatidylcholine, also known as lecithin)
Sphingolipids
- are important constituents of cell membranes
- contain a hydrophilic region and two fatty acid–derived hydrophobic tails.
- various sphingolipids differ primarily in the identity of their hydrophilic regions
4 classes of sphingolipids
ceramide, sphingomyelins,
cerebrosides, and gangliosides
Uses of cholesterol in the cell membrane
- regulates membrane fluidity
- necessary in the synthesis of all steroids, which are derived from cholesterol
- stabilizes adjacent phospholipids, it also occupies space between them preventing the formation of crystal structures in the membrane & increasing fluidity at lower temperatures; At
high temperatures, cholesterol has the opposite effect: by limiting movement of phospholipids within the bilayer, it decreases fluidity and helps hold the membrane intact - Composes about 20 percent of the cell membrane; by mole fraction, it makes up about half. This large ratio of cholesterol to phospholipid ensures that the membrane remains fluid.
How is membrane stability maintained in the phospholipid bilayer?
- derived from interactions with both the hydrophilic and hydrophobic regions that make up the phospholipid bilayer
Why aren’t waxes found in animal cell membranes?
- B/c they’re lipids that are extremely hydrophobic, so they’re sometimes found in cell membranes of plants
Uses of waxes in plant cell membrane
- waxes can provide both stability and rigidity within the nonpolar tail region only
- serve an extracellular function in protection or waterproofing
Fluid mosaic model
- Accounts for the presence of three types of membrane proteins: Transmembrane, Embedded, & Membrane-associated (peripheral) proteins
Transmembrane proteins
- Proteins that pass completely through the lipid bilayer
- Ex: Transporters, channels, and receptors