functions of the membrane correct answer: -the structure of the membrane is key for its function
-act as a barrier regulating import and export of molecules
-help with compartmentalization of the cell, creating particular environments for certain processes so multiple specialized processes c...
BCH210 TEST 2 Questions
With Complete Solutions
functions of the membrane correct answer: -the structure of the
membrane is key for its function
-act as a barrier regulating import and export of molecules
-help with compartmentalization of the cell, creating particular
environments for certain processes so multiple specialized
processes could occur at once
-modulates cell-cell recognition with their glycoproteins and
glycolipids located on the outer leaflet facing the cytosol
-signaling across the membrane by proteins and lipids
properties of the membrane correct answer: -lipids bilayers
impermeable to polar or changed molecules (can't go through
membrane without the help of a transmembrane protein)
-formed due to the hydrophobic effect (the lipids aggregating in
water and bury their hydrophobic tails in the inner leaflet and
their polar heads interact with water)
-formation is due to non covalent interactions
-asymmetric-each leaflet is made up of different proteins and
lipids which allows for specific interactions on each leaflet
-the lipid heads on the outside and the tails on the inside
-in a lipid bilayer, the tails are interacting through van der waals
interactions
,-the lipids could diffuse laterally (side to side within the same
membrane) or move to another leaflet with the help of an
enzyme
-composed of lipids and proteins which may or may not have a
carbohydrate covalently bound to the outer leaflet
-membrane is fluid due to lipids and cholesterol- allows for a
conformational change in order for signals to be transmitted
across the membrane and for molecules to be bound
membrane protein function correct answer: -involved in
transporting molecules and the transduction of info across the
membrane
fluid mosaic model correct answer: model that describes the
arrangement and movement of the molecules that make up a cell
membrane
-the movement of lipid and membrane proteins differs
significantly in samples of pure lipids vs biological membranes
fluid- the membrane components can move quite rapidly in the
plane of the membrane
Mosaic-diverse mixture of lipids, proteins and carbs
how are membranes asymmetric correct answer: -due to flip
flop diffusion facilitated by flipases+ floppases because the mov
of lipids from one leaflet to the other is very slow because the
core is hydrophobic (energetically unfavourable) (flipase only
works on PS and PE and floppase (works on any) uses atp but
not scamblase)
,-they move lipids that have a polar/charged groups attached to
their head group across the hydrophobic membrane interior
causing the membrane to be asymmetric using ATP hydrolysis
-they create an environment to allow us to move charged groups
through the hydrophobic region
-scramblases gets rid of membrane asymmetry
-2 leaflets to make a bilayer of the membrane
-each leaflet is made up of different proteins and lipids which
allows for specific interactions on each leaflet- allows for
different processes to occur along the membrane
glycoproteins and glycolipids correct answer: -post translation
modification involving a covalent attachment of a sugar on the
lipid or protein done by an enzyme called transferase
Glycoprotein= membrane proteins + sugar
glycolipid=lipid proteins+ sugar
-found on the outer leaflet (no sugars on the inner leaflet) and
help with cell-cell recognition
-the modification helps with protein folding and membrane
insertion
Flippases correct answer: p type ATPase
-moves PE and PS from outer to cytosolic leaflets
-translocase
floppases correct answer: (ABC transporter) moves
phospholipids from cytosolic to outer leaflet
-type of translocase
, Scramblases correct answer: move lipids in either direction
towards equilibrium (down the concentration gradient)
FRAP correct answer: fluorescence recovery after
photobleaching to observe how the lipids within a bilayer
diffuse laterally (membrane dynamics)
-the lateral diffusion of proteins depends on interactions with
other proteins (ie cytoskeleton) or extracellular components-will
effect if the protein could move along the plain. Movement is
tracked by single molecule tracking fluorescence
1. label cell surface molecule by covalently attaching a molecule
that fluoresces when it is hit with light
2. use a laser to bleach the fluorophore in a small part of the
membrane so that region doesn't fluoresce
3. measure the mobility of the lipids into the affected region so
that the region is uniformed again. they recover the region by
diffusion laterally
Results:
-there is high intensity of fluoresce before the bleached
-after bleached, there is an increasing fluorescence intensity as
time goes on
-some proteins and lipids could spend more time confined
within certain regions which slows down the recovery rate
forming lipid rafts (microdomains)
single molecule tracking fluorescence correct answer: -for
membrane proteins
add a fluorescent lipid on the the membrane and track where it
goes
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