Membranes protein structure Flashcards
what are the essential functions of membranes
they act as barriers and also support localization of the cell so it can do lots of different things in different places
what mediates signaling across membranes
proteins and lipids
what allows for the cell membrane to regulate cell-cell communication
glycoproteins and glycolipids
what is responsible for membrane formation
a decrease in ionic interactions with water. this is basically the hydrophobic effect
are membranes asymmetrical or symmetrical
they are asymmetrical composed of lipids and proteins
what mediates the process of proteins carrying molecules and signals being transmitted across the membrane
conformation changes
____ and ____ play an important role in membrane fluidity
lipids and cholesterol
What recent modifications have been made to the fluid mosaic model
the movement of lipids is restricted based on if they are in pure lipids or biological membranes
What technique is useful in measuring membrane movement
FRAP (fluorescence recovery after photobleaching)
lipid raft
area in the membrane where lipids tend to hang out for a longer period of time
What does the addition of sugars and proteins to the membrane post-translationally impact?
cell recognition and membrane insertion
Flip-Flop diffusion
movement of lipids from one leaflet to the other
is flip flop diffusion energetically favourable or unfavourable?
unfavourable
How do enzymes mediate membrane asymmetry
by creating active sites and spaces on the membrane
Flippase
ATP dependent translocase that moves lipids to the inner leaflet
Floppase
contains an active site and it moves things to the outer leaflet
Scramblase
ATP independent enzyme that is less specific and will be used to even out the lipids across the membrane. Moves all lipids down their concentration gradient
ensures that there is not too much flipping or flopping and the lipids are unbalanced
Lipids
molecules involved in providing structural support for cells and organelles
what defines classes of lipids
their physical properties, ie. whether they are hydrophobic or amphipathic
What type of lipids are involved in metabolism
triacylglycerides (carbon storage)
what lipids are important for the structure of membranes
phospholipids
sphingolipids
glycolipids
sterols
at physiological pH will fatty acids be deprotonated or protonated
deprotonated because its pka<pH
what is a saturated fatty acid
this is a fatty acid with single bonds
what is an unsaturated fatty acid
contains double bonds
what is the usual numbering of double bonds in fatty acids
they are numbered relative to the carboxylic acid but it can also be named relative to the methyl group for omega fatty acids
Fatty acid nomenclature
C’s : # of double bonds
what makes a fatty acid an omega fatty acid ?
the location of the double bond. a fatty acid is considered an omega fatty acid when the double bond is situated three or six carbons away from the methyl group
what does delta refer to?
this is when we label carbons relative to the carboxylic group
What are considered the good fats
unsaturated and omega fats
what type of fats decrease membrane fluidity
saturated fats because they form lots of non-covalent bonds that act like glue
What about unsaturated fats increase membrane fluidity
they have kinks that participate in cis double bonds, increasing fluidity by causing there to be more room in the membrane
what does a higher melting temperature of lipids mean?
a higher Tm means that there are more covalent bonds that need to be broken
if a membrane has a higher Tm does it mean it is more or less fluid?
it would be less fluid because a higher temperature means it is more rigid and contain more non-covalent interactions that need to be broken down
Tri-acyl-glycerols (TAGs)
3 fatty acids attached to a glycerol
what attaches the fatty acids to the glycerol
ester linkage
what are tags good for
they are good for storing carbon that can be used for energy
how are amphipathic molecules made?
By attaching fatty acyl chains to polar (OH, sugar, or phosphate) head groups
what is the most common steroid found in membranes?
hydrophobic cholesterol
Glycerophospholipids
they contain 2 fatty acid tails with a glycerol head and a phosphate group
examples of glycerophospholipids
phosphatidylethanolamine (PE) and PS.
these bind to flippase
sphingolipids
lipids that contain 1 fatty acid bounded to N on sphingosine
examples of sphingolipids
sphingomyelin and gangliosides
cholesterol
can be metabolized to other hormones needed for dietary lipid absorption
can form lipid rafts
three types of membrane lipids
glycerophospholipids, sphingolipids, and cholesterol
peripheral membrane proteins
located on the outside of the membrane that either interacts with outer or inner leaflets by non-covalent interactions
Integral membrane proteins
span membrane
what is the difference between peripheral and integral proteins
removal
how can peripheral membrane proteins be removed
by milder conditions like increasing salt in pH
how are integral membrane proteins removed
through more harsh conditions like detergents that break apart the membrane
how are lipid anchored proteins removed? why?
they also require harsher detergents because their tails are covalently attached to the amino side chains and functional groups
for membrane proteins what extra steps are taken during protein purification
adding detergents
Critical micelle concentration (CMC)
concentration at which the detergent spontaneously forms stable micelle structures
what does it mean for a concentration above CMC
sufficient enough for you to extract protein from membrane
how can you predict membrane spanning segments
by scanning primary sequences for long stretches of hydrophobic amino acids that represent TM segments
hydropathy scale
takes into consideration factors about amino acids that could indicate transmembrane segments
why does a negative hydropath index indicate
more polar segments
what does a positive hydropathy index indicate
more non-polar/hydrophobic segments
how can you read a topology chart to indicate a transmembrane protein
high peaks that are 20 amino acids wide
