BIO 2 EXAM 1 Membrane Strucutre

Question 1

Defining Membrane Structure…

Answer 1

Phospholipids are amphipathic

But biological systems are mostly aqueous

Hydrophobic tails will cluster together to avoid water (two types):
One possibility is a micelle, Alternatively, a phospholipid bilayer

A thin barrier effectively blocks most molecules
Size
Charge/Polarity

Lipids are trapped on only one leaflet inner and outer

Question 2

All biological membranes are based on…

Answer 2

phospholipid bilayers

Plasma membrane and organelle membranes

Question 3

Membranes are not just phospholipids, but also…

Answer 3

Proteins:
Integral and Peripheral

Steroids

Question 4

Defining Membrane Domains…

Answer 4

have a domain with a hydrophobic surface

Maybe a single a helix

Could be a post-translational modification

Fluidity has its limits

Some cell types restrict diffusion

Question 5

Defining Membrane Fluidity…

Answer 5

Frye-Edidin Experiment: Labeled proteins on a cell to fluoresce either red or green. Fuse cells and observe

Membranes are a two-dimensional fluid

Fluid mosaic model

No flipping!

Question 6

Membrane fluidity is controlled by…

Answer 6

by which lipids are present

More unsaturations in the tails lead to more fluidity (also more permeability)

Shorter fatty acid tails leads to more fluidity (also more permeability)

Steroids buffer fluidity

At most temperatures, steroids decrease fluidity

At low temperatures, steroids increase fluidity

Question 7

Defining Lipid Rafts and Glycocalyx…

Answer 7

LR:
Fluidity has its limits
Some lipids and proteins clump together

Gly:
Most animal cells have a “carbohydrate coat”: the glycocalyx
Glycoproteins
Glycolipids

Maybe hundreds of monosaccharides
Important for cell-cell recognition