Lecture 10 Information Flashcards
Fluid mosaic model
the proteins and the phsopholipids themsleves are moving within the plane of the membrane
How do constituents of the cell membrane move?
through non-covalent weak interactions, allows for lots of curvature and flow
Micelle
individual units are wedged shape
lipid tails funnel inwards and heads are water
Vesicles
lipid bilayer with aqueous cavity
beginning of life on earth
What is bilayer formation driven by?
hydrophobic interactions and increasing entropy in the aqueous outside environment
Are the two layers of the bilayer membrane symmetric?
No
The two layers are asymmetric and the inner/outer leaflets can have different lipid constituents
Integral membrane proteins
imbedded in the protein
have membrane spanning sections
amino acids are hydrophobic
How can integral membrane proteins be removed?
detergents interact with the hydrophobic regions and remove integral membranes
Peripheral membrane proteins
associated with other proteins/components of the membrane
Not imbedded in the membrane or held covalently to the membrane
Associated to membrane through weak interactions
Amphitropic membrane proteins
association with membrane is biologically regulated
can have covalent interactions with the membrane
dynamic association
Transmembrane alpha-helicies
strongly anchor proteins in the membrane
can have one or multiple helicies
regions with high hydropathy on a plot can indicate where transmembrane alpha-helicies lie
Example of a transmembrane alpha-helix
bacteriorhodopsin-7
membrane spanning protein
Trp and Tyr residues in membranes
located at the interface (intersection of hydrophillic and hydrophobic regions) of the membranes
amphipathic quality of their R-groups allows for them to mediate between hydrophillic outer surface and hydrophobic intersurface
Where do positively charged amino acids tend to be located in the membrane?
on the inner leaflet of the cell
the cell tends to be negatively charged, so the positive amino acids interact with the negatively charged cell interior
The beta barrels
not as predictable or long as membrane spanning alpha helicies
beta sheet R groups are pointing out of the plane and into the plan in an alternating manner
Lipid linked membrane proteins
proteins are covalently attached to some membrane anchoring lipid
only found on the inner leaflet
Examples of lipid linked membrane proteins
Phosphatidylserine and PIP2
GPI proteins
found only on extracellular surface of the cell
in general, carbohydrate groups are found on the outside of the cell membrane in order to serve as cellular identification
ex: blood type sphingolipids
What happens to membrane fluidity if temp is under the physiological temp?
enter the gel phase with restricted motion and paracystalline structures
too rigid
What happens to membrane fluidity if temp is above the physiological temp?
liquid disordered state, too much fluidity and the cell might start letting in molecules that it shouldn’t
What happens to membrane fluidity when temp is at the physiological temp?
At the physiological temp, liquid ordered state, less thermal motion, but still allows for lateral movement in the plane of the bilayer
What type of lipids does the membrane use at higher temperatures?
lipids that are more saturated, making the membrane less fluid
*reverse is true at lower temps
How to visualize cholesterol?
acts like a barrel floating on top of the cell membrane
Cholesterol at high temperatures
the barrels will impede the movement of water
water bumps into the barrel and stops
Cholesterol at low temperatures
cholesterol stops the water molecules from associating with each other (barrels are physically in the way)
increases fluidity
hop diffusion
moves lipids to different regions of the membrane very quickly
then, fast local movement occurs within a region
Why is moving of phospholipids from one leaflet to the other unfavored?
Inside of membrane is hydrophobic, so it is hard to get hydrophilic head to move through the hydrophobic region to the other side
Why do we need to regulate lipid movement from one leaflet to the other?
over time, an equillibrium would be reached and the membrane would become symmetric
Flipases
take aminophospholipids (PE and PS) on the extracellular leaflet and move to cytosolic leaflet
requires ATP
Flip extracellular leaflets that might signal apoptosis to the inside, so apoptosis is not triggered
Floppase
take phospholipids on the intracellular leaflet and flip them to the extracellular leaflet
Require ATP
Scramblase
scrambles the concentrations of phospholipids in the membrane and opens the door for the phospholipids to move down their natural concentration gradients
Phospholipids will approach equilibrium/symmetric gradient faster
Scramblases have a role in apoptosis
ATP not needed since moving phospholipids down their concentration gradient
Lipid rafts
areas of the bilayer are thicker because they are composed of phospholipids that have longer chains of fatty acids
made of glycosphingolipids (gangliosides/cerebrosides)
saturated fatty acids
What do lipid rafts create?
regions with specific proteins associated that controls the chemistry in these regions
specific environment within the membrane
Simple diffusion
small hydrophobic molecules can get through the membrane
Facilitated diffusion
going down a concentration gradient
No ATP required
using a protein to allow molecule to travel down the gradient
Ion channels
free flow of materials through the membrane, mostly using the concentration gradient
generally don’t use ATP
Uniport
moves one molecule down gradient
Synport
moves two molecules in the same direction
Antiport
moves two molecules in different directions
Differences between transporters and channels
Transporters bind the molecule with high selectively and can be saturated
Transporters do not increase rate that much compared to channels
Channels carry molecules with low selectively
Aquaporins
a type of channel
move water through membrane at high rate
Aquaporins and hydronium
prevent hydronium from passing through by placing positively charged histidine and asparagine within the interior of the porin
NPA sequence
aparaginine proline and aspartate
Asparagine is able to hydrogen bond to water
By replacing hydrogen bonds between water and water, with water and asparagine we keep the movement of water energetically favorable
How do you regulate and turn off the flow of water?
phosphylate at serine
Changes the structure and removes NPA regions from central region and water cannot go through the aquaporin
GLUT1
a type of passive transporter for glucose
made up of alpha helicies with hydrophobic outside and hydrophillic inside
Chloride-bicarbonate exchanger
another type of passive transporter
exchanges chloride for bicarbonate as bicarbonate is pushed out of the cell
negative for negative charge maintains electrical balance
antiport: two molecules move in different directions
no ATP since moving with the gradient
Pumps
move solutes up concentration gradient and require ATP
Primary active
solute accumulation coupled directly to an exergonic reaction (like ATP hydrolysis)
Secondary active
endergonic transport of one solute couples to the exergonic flow of another solute that was originally pumped uphill by a primary active pump
Sodium-Potassium pump
primary active transporter
antiport: 2 K+ comes in and 3 Na+ goes out
Cotransporter: phosphorylation of a critical Asp causes conformational changes
Lactose transporter
secondary active transporter
Initial endergonic pumping of H+ out / the exergonic flow of H+ in is coupled to allow lactose to flow against its gradient
After H+s are pumped against their gradient, they fall back down their natural gradient and take lactose with them
Hydrogen cyanide
blocks the proton gradient and therefore blocks lactose from flowing into cell
does the same thing with ATP synthesis
What prevents phospholipids from moving from leaflet to leaflet?
high energetic cost of moving the hydrophilic heads across the hydrophobic interior
Where are phosphatidylethanoalmine and phosphatidylserine found?
on the inner membrane leaflet
Where are phosphatidylcholin and sphingomyelin found?
on the outer membrane leaflet
