BCH210 TT2 Questions With
Complete Solutions
Functions of biological membranes correct answer: - barrier
(import/export)
-compartmentalization of essential molecules (incrs. efficiency)
- cell signaling-mediated by pr & lipids (receptors)
- modulate cell-cell recognition (glycoproteins & glycolipids)
What's responsible for membrane formation correct answer:
decrease in ionic interactions w/ h2o (HYDROPHOBIC
EFFECT)
-h20X tails aggregate to hide from h2o (lots of n-c interactions)
-polar heads interact w/ h2o
Decreases membrane entropy
Membrane properties correct answer: -Selectively permeable
(small np), self repairing, barrier, flexible and continuous.
-Impermeable to polar/charged molecules
-Asymmetric, proteins have the same orientation but lipid
composition of the bilayer is different. Could be covalently
bound to sugars on EXC side
-most membranes have net diff in charge across bilayer bc of
enzymes
glycoproteins and glycolipids correct answer: -added chain of
oligosaccharides
-ALL biological membranes
,-PTM after synth
-protein folding & membrane insertion
-attachment done by transferases
-exterior of cells
-Cell-cell recognition
Flippase correct answer: (P-type ATPase) (Translocase)
-moves PE and PS from outer to cytosolic leaflet
-FLIP IN
-driven by ATP hydrolysis
Floppase correct answer: (ABC transporter) (Translocase)
-moves phospholipids from cytosolic to outer leaflet
-FLOP OUT
-driven by ATP hydrolysis
Scramblase correct answer: -translocates random phospholipids
between two monolayers randomly, resulting in an equal
distribution
-lipids in either direction
-toward eq (down concentration gradient)
membrane asymmetry correct answer: -Types of phospholipids
(PE PS inside) translocates even it out
-glycopr/lipids on outside
-ER synthesis provides proper orientation
-membrane proteins
FRAP (fluorescence recovery after photobleaching) correct
answer: Measures speed of lateral diffusion of phospholipids in
LIVE cell
, 1. Label cell surface (ex. GFP on lipids)
2. use high intensity laser to bleach small area
3. measure speed of other molecules into the region (ie. how fast
is recovery of fluorescence)
Can say how fluid the membrane is
- impacted by interactions with other components in cell or stuck
in regions like lipid rafts
1. How much light returns relative to the amount of light that
was there before the photobleaching? This is the 'percent
recovery'.
2. How fast did the fluorescent molecules migrate back into the
photobleached area? This is a measurement of the 'diffusional
mobility'.
● Application: FRAP can determine if a protein is able to move
within a membrane (high percent recovery with fast mobility),
or whether it is tethered other structural components of the cell
(low percent recovery with slow mobility).
SDS & FRAP correct answer: SDS breaks membrane--> no
FRAP
Crosslinker & FRAP correct answer: lipids link together, FRAP
is slowed
Single-molecule tracking fluorescence microscopy correct
answer: monitor movement of fluorescent molecules in
membrane
some pr & lipids can be stuck in areas for certain time ie. lipid
rafts (micro domain w/ function)
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