Membrane Structure and Function

Every cell on earth is enveloped by a __ membrane, a thin fatty film. The membrane is composed of a lipid __ that is about 5nm or 50 atoms thick. The membrane is a __ that keeps cell contents in (and outside contents out), while at the same allowing exchange of material between the inside and outside

plasma : bilayer : barrier

__ also have membranes that function the same way as the plasma membrane:

-__ membranes: Envelops the cytoplasm and involved in communication, cell growth, metabolite exchange

-__ membranes: Surround __, ER, Golgi, etc. and form intracellular compartments

Organelles : External : Internal : nucleus

Plasma Membranes are Lipid Bilayer: Composed of __. They are embedded with different __

phospolipids : proteins

Lipids have __ (“water-loving”) heads and __ (“water-fearing”) tails. Membrane lipids are therefore considered __ (having both hydrophilic and hydrophobic properties). …molecules like sterol and glycolipids often assemble in cell membranes

hydrophilic : hydrophobic : amphipathic

__ are the most common type of lipid in the cell membrane, with __ (the head contains choline) being the most common type of phospholipid (of _)

Phospholipids : phosphatidylcholine : 7

Phospholipids: The hydrophobic tail is composed of __ chains. The hydrophilic head group is composed of a __ plus and additional __. A common modification is the addition of a choline groups from phosphatidylcholine.

nonpolar hydrocarbon : phosphate : polar group

The amphipathic nature of lipids, like phosphatidylcholine, cause the to __ into a bilayer. Lipid bilayer sheets are __ because they have an open edge where the non-polar tails are exposed. Self assembling into a sphere completely isolates the hydrophobic regions : The most stable configuration are __ (e.g. cells)

assemble : unstable : spheres

The Lipid Bilayer is a Two-Dimensional __

Fluid

The plasma membrane is not static, it is __(i.e. bendable) AND is fluid (i.e. the lipid molecules can shift side to side). Fluidity depends on temperature; the warmer the membrane, the more fluid it become. Fluidity depends on two major properties of the phospholipid tails: __ and number of __

flexible : Length : double bonds

The phospholipid bilayer is two-dimensional moving liquid layer: Movement and diffusion of individual phospholipid molecules are possible. __ and rotation is common and frequent. __ is not. Flip-flop can be catalyzed by enzymes. The fluidity of the phospholipid bilayer leads to the __ model of cell membranes

Lateral diffusion : Flip-flop : fluid mosaic

Fluid Mosaic Model:

Fluidity of the phospholipids allows embedded protein molecule to __ through the layer. Embedded protein __ flip-flop. Protein movement can be __ if they are tethered to the cell cortex

diffuse : cannot : restricted

Hydrocarbon tails vary between __ carbons in length. Most tails are __ carbons long. Shorter tails lead to increased fluidity (less tail interactions)

14-24 : 18-20 :

Tails that contain double bone (__) are kinked and lead to more fluidity, whereas saturated tails have no kinks and lead to less fluidity (i.e. more tail interactions)

unsaturated

__ lipids tend to be unsaturated and therefore more fluid (e.g. canola oil)

plant

__ lipids tend to be saturated and therefore less fluid (e.g. lard, butter, bacon grease)

animal

Cholesterol is found in __ lipids (up to 20% of total lipids), which helps to add __ to animal membranes

animal : rigidity

The lipid Bilayer is Asymmetrical: __ (sugar lipids) are often found on the outside of the membrane. The different sides of a lipid bilayer have different __ and encounter very different environments, so their sides are necessarily quite different (i.e. __)

Glycolipids : functions : asymmetrical