Membrane Structure and Function Flashcards
What percentage of cell membranes is made up of proteins? Lipids?
50% lipids and 50% proteins
Although depending on the cell type, the proteins can range from 25% (in neurons) and 75% (in mitochondria)
What features of fatty acid tails dictate membrane fluidity?
Length and saturation
How does a cis-double bond impact fatty acid structure?
Cis-double bonds induce a kink that prevents phosphoglycerides from packing too tightly
Describe the general structure of phospholipids.
A glycerol molecule has two fatty acid chains bound to adjacent carbons, and a phosphatidyl group bound to the other carbon
What does cholesterol incorporation into a lipid bilayer cause?
Increased rigidity of the membrane
Decreased permeability of the bilayer to water soluble molecules
What is the maximum ratio of cholesterol to phospholipids in a cell membrane?
1:1
What is self-aggregation?
Amphipathic molecules automatically organize themselves so that the hydrophilic portions are in contact with water and the hydrophobic portions are protected from water
Example: Micelles
What structure makes all life on earth possible?
The lipid bilayer
Describe the ways that phospholipids can move throughout lipid membranes.
Lateral diffusion
Flexion
Rotation
Flip flop (rarely occurs)
What is membrane fluidity?
The relative mobility of lipids within a membrane
How is fluidity related to transition temperature?
More fluid membranes have lower transition temperatures
Two phospholipids have the same length fatty acid tails, but one has double bonds and the other doesnt.
Which will have the lower transition temperature?
The phospholipid with more double bonds will have a lower transition temprature, and thus more fluidity
How does length of hydrocarbon tails affect fluidity?
Shorter hydrocarbon tails will have more fluidity (lower transition temperature)
What are lipid rafts?
Membrane microdomains that contain protein complexes associated with specific lipids that move around as one unit
What molecules are found only on the exterior face of the plama membrane contributing to the asymmetry of the lipid bilayer?
Glycolipids are only found on the extracellular side of the cell membrane.
These are branched structures made up of several sugar moieties
What does translocation of the PS protein cause?
PS on the outside layer of the lipid membrane tells macrophages to “eat me”
A scramblase enzyme flips the PS from the intracellular side to the extracellular side following apoptotic signals
What role does phosphatidylserine play in membrane structure/function?
It is found on the interior side of the plasma membrane which leads to a net negative charge on the inner membrane compared to the outer memrane
What does phospholipase C do?
Cleaves inositol phospholipids to generate relay
Signal and scaffold for protein kinase C
How can Galectin 3 be used for imaging?
Galectins contain a carbohydrate recognition domain (CRD) that allows them to bind sugars present on surface proteins
Galectins are usually only found within the cytoplasm, where no sugars are accessible
When viruses, bacterio or other pathological agents rupture phagosomes/endosomes/lysosomes, the sugars normally present on the inside of the vesicle become accessible to Gal3
What secondary structure is commonly found spanning the lipid bilayer?
Alpha helices with hydrophobic residues throughout
What does a hydropathy plot show?
The plot shows the hydrophobicity of an entire amino acid chain
Positive peaks correspond with hydrophobic regions that most likely span the membrane
What are the different ways that a protein can associate with the cytoplasmic leaflet of the plasma membrane?
Myristoyl anchor via an amide linkage
Palmitoyl anchor via a thioester linkage
Farnesyl anchor via a thioether linkage
Would you expect the inside of a beta barrel to have many hydrophillic or hydrophobic residues?
Hydrophilic
These structures often function as channels through which molecules can enter the cytosol from the extracellular space
What feature of membrane proteins does FRAP experiments demonstrate?
FRAP = fluorescence recovery after photobleaching
These experiments demonstrate the many membrane proteins diffuse laterally within the plasma membrane
Describe the immunological synapse
Cell to cell contact induces clustering of cellular components (transmembrane proteins, actin and lipid rafts) at the point of contact
