cell bio exam 2: cell membranes and membrane trafficking

important cellular functions of the plasma membrane

• receiving information - signal transduction

• import and export of small molecules - contains channels and transporters

• capacity for movement and expansion, cytoskeleton-driven

what two aspects of membrane composition can change, affecting their properties?

• lipid composition

• protein composition

what is primarily responsible for defining the function of a lipid bilayer?

protein content

membrane proteins can associate with the lipid bilayer in four ways:

• transmembrane proteins

• monolayer-associated membrane proteins

• lipid-linked membrane proteins

• peripheral membrane proteins

integral membrane proteins

permanently embedded in the lipid bilayer

include:

• transmembrane proteins

• monolayer-associated membrane proteins

• lipid-linked membrane proteins

transmembrane proteins

extend across the lipid bilayer

monolayer-associated membrane proteins

anchored to the cytosolic half of the lipid bilayer with a hydrophilic part

lipid-linked membrane proteins

linked to the bilayer by a covalently attached lipid molecule

peripheral membrane proteins

• NOT integral membrane proteins

• attached to the membrane by noncovalent interactions with membrane proteins

phospholipids are amphipathic, meaning they have

both hydrophilic parts (head) and hydrophobic parts (tails)

lipids assemble into bilayers because

it is an energetically favorable arrangement, where hydrophobic parts are kept with hydrophobic parts and hydrophilic parts are kept with hydrophilic parts

key classes of membrane lipids are all amphipathic and include

• phospholipids

• cholesterol

• glycolipids

hydrophilic heads + hydrophobic tailsw

which type of membrane lipid is only found in the non-cytosolic leaflet?

glycolipids - interact with cell signaling

is cholesterol distributed equally in both leaflets?

yes

kinks have this effect on membrane fluidity, while cholesterol has this effect

increase fluidity; stiffen

how does fluorescence recovery after photo bleaching (frap) work?

• measures membrane fluidity

• membrane proteins labeled with GFP

• small area of membrane is permanently bleached using laser

• bleached molecules diffuse away and surrounding unbleached fluorescent molecules shift towards recovery - rate and extent indicates fluidity

during mechanisms like vesicular transport, membranes retain their orientation. this means that

• the cytosolic and noncytosolic faces are maintained in the same orientation

• orientation of proteins also stays the same

plasma membrane proteins have a variety of functions and can include

• membrane transporters and channels

• membrane anchor proteins - allow attachment of cells to ECM, e/o, or cytoskeleton

• receptor proteins

• enzymes