Flashcards in chapter 10.1 (membrane structure) Deck (66):
What is the general rule when dealing with membrane proteins?
The metabolically active the more membrane proteins it contains
What is the protein composition of inner mito?
electron transport chain proteins
proteins that synthesize ATP
What is the protein composition of myelin sheaths?
serves as a insulator of nerve axon with lipids
myelin sheaths provide barrier for nerve axon
What are integral proteins?
all proteins that are fully or partially embedded in lipid bilayer
What are transmembrane proteins?
proteins that goes through the plasma membrane one or more times
What are the domains of transmembrane proteins?
What are various types of transmembrane proteins?
What does the membrane spanning domains of transmembrane proteins usually contain?
helices that are 20-30 AAsand have hydrophobic R-groups
What does the lack of water within the bilayer promotes?
H-bonding between polypeptide backbone
What is a hydropathy plot?
allows for visualization of the hydrophobicity of a polypeptide that span the lipid bilayer.
assigns a positive number for the more hydrophobic R group
if a segment is more hydrophobic it shows up on the plot
What other forms may a membrane spanning protein form?
a membrane spanning structures formed from pleated sheets (beta barrels)
What is the length of the beta barrels?
~10 AA shorter than with helix
polypeptide crosses the membrane several times
how many strands are involved in forming the beta barrel?
In which organisms are beta barrels usually found?
in bacteria membrane
outer membrane of mito/Chloroplast
What are monotopic integral proteins?
integral proteins that are only on side of a leaflet
What are the characteristics of a monotopic cystolic leaflet protein?
an amphipatic helix that has one hydrophobic surface within the cystolic leaflet. and one surface that interacts with the aqueous cytoplasm
What do monotopic cystolic leaflet proteins all have?
a significant hydrophobic surface and all are insoluble in aqueous solution
What are peripheral proteins?
- hydrophilic proteins associated with polar regions of other membrane proteins or the polar head groups of lipids. They are soluble in aqueous solution
What kind of bonds does peripheral proteins make with other membrane proteins?
association with membrane proteins usually by ionic and H-bonds (occasionally, disulfide bonds may be involved)
How can peripheral proteins be removed from the membrane?
removable from membrane w/ mild dissociation techniques b/c they are primarily hydrophilic and not hydrophobic
What are lipid linked proteins?
proteins are covalently attached to lipids within the bilayer
What are the different types of lipid anchors?
Fatty acid chain
What can a fatty acid chain do to a protein?
• single fatty acid chains can either stabilize a membrane spanning protein or be added after protein synthesis and attach a primarily soluble protein to the membrane
What is a GPI anchor?
made from a glycosylated PI phospholipid
When are GPI anchors added to a protein?
While the protein is being synthesized in the ER
What is the purpose of a GPI anchor?
links the protein to extracellular leaflet of the bilayer
How can lipid bilayer form?
form spontaneously from certain amphipathic lipids in aqueous solutions
What is the energy of bilayers?
the most stable (lowest free energy) association of phospholipids
What is the structure formed by lipid bilayers dependent on?
the type of phospholipid
What do bilayers and micelles do?
allow maximum contact of hydrophilic regions with H2O while shielding hydrophobic regions from H2O
What are micelles?
solid drops of lipid, formed from the aggregation of single fatty acids
What will groups of phosopholipids with two hydrocarbon tails will naturally form?
a bilayer in artificial or biological systems
What do lipid bilayers spontaneously form?
water filled spheres
What do phospholipid spheres minimize?
minimize free hydrophobic edge interactions w/ H2O and thus minimizes the free energy of the lipid/water interaction
What do the phospholipid bilayer allow?
sealing holes in membrane and membrane fusion.
implication for evolution of cell
What are liposomes?
artificially formed membrane spheres that are sometimes used to deliver large hydrophobic molecules into cells (eg, gene therapy, chemotherapy)
What are liposomes often used for?
a. often used in medicine to introduce polar compounds into cells
What are liposomes similar too?
b. essentially similar in structure to vesicles found in cells (without the usual proteins)
How do the lipid molecules interact with one another?
None of the lipid molecules in a membrane are covalently bound to each other
Lipids interact purely by hydrophobic interactions; thus all the lipid molecules are free to move within the bilayer
How doe the lipid bilayer move?
The bilayer acts as a 2-D fluid (restricted to lateral movement in x and y planes, not out of membrane, in the z-plane)
What are the movements of the lipid bilayer?
What is the lateral movement of phospholipids?
movement of lipids within one plane of bilayer, within a leaflet/monolayer
What is the rate of lateral movement of a phospholipid?
rate of diffusion ~ 10-8 cm2/sec
a single lipid molecule can move completely around a bacterial cell in 1 sec
What is flip flop movement of lipids?
exchange between the two leaflets of a lipid bilayer
What is the rate of flip-flop movement of a lipid?
rare, slow (1 spontaneous, non-catalyzed event/day) due to polar head group having to move through lipid core
What are the evidence of membrane fluidity?
FRAP = fluorescent recovery after photobleaching
What affects the how lipids and proteins move laterally within the bilayer and interact with one another?
fluidity of the membrane
What happens it the membrane is to rigid?
it takes too long for proteins to interact if necessary
some proteins have to diffuse along the bilayer to reach their target interaction
What happens if a membrane is too fluid?
membrane is leaky and an ineffective barrier
What is membrane fluidity dependent on?
types of fatty acids in phospholipids
What is the affect if the membrane is warm?
more fluid membrane (membrane melts)
What is the affect in colder membranes?
less fluid/more solid membrane (membrane freezes
What will be characteristic of artificial bilayers made from a single type of phospholipid?
melting and freezing points
What affect does phospholipids with shorter chain fatty acids have on fluidity?
more fluid (have lower melting points)
What affect does phospholipids with longer fatty acid chains have on fluidity?
less fluid (have higher melting points)
What affect does phospholipids with C=C bonds have on fluidity?
cis double bonds forms a kink, prevents lipids from packing tightly together.
What type of tails does phospholipids usually have?
usually one unsaturated tail and one saturated tail
What is the response to temperature change in membrane proportional too?
the various type of lipids within that membrane
What is the role of cholesterol in animal cell membranes?
Due to its (weak) amphipathicity, cholesterol fits into bilayer in specific manner
Helps “plug gaps” between phospholipids, making membrane more stiff (similar to decreasing fluidity) and less permeable to water and small molecules
What do cells want to do with membrane fluidity?
keep it relatively constant to maintain proper function
what is proper fluidity is essential for?
mobility (function) of specific integral proteins and lipids
What is homeviscous adaptation?
the ability of species to modify the viscosity of lipids
What is the range that species keep the bilayer fluid at their body temperature?
What are poikilothermic organisms?
organisms who body temperature fluctuate wit the environment
Why is regulating bilayer fluidity important to poikilothermic organisms?
because their body temperature is dependent on the environment, if fluidity gets too fluid or rigid it will interrupt the normal function of the cell