chapter 11 Flashcards
1
Q
how is the structure of the p.m. commonly described in terms of?
A
- the fluid mosaic model, which states that biological membranes are 2D, fluid structures within which lipid and protein molecules diffuse freely
2
Q
what 2 main structural factors affect the stability of the p.m.?
A
- lipid rafts, which are held together by large amounts of cholesterol and contain relatively high concenteations of sphingomyelins. they can diffuse within the lipid bilayer and their main functions include contributing to the fluidity of the memrane and helping to regulate signaling processes
3
Q
how does cholesterol help modualte the fluiditiy of the p.m. at a range of temperatures?
A
- at high temperatures, including physiological temp. cholesterol decreases membrane fluidity by impeding the diffusion of phospholipids within the bilayer
- at low temperatures, cholesterol increases membrane fluidity by preventing phospholipid tails from clustering together
4
Q
unsaturated fatty acud tails promote fluidity by preventing the tails from stacking, as can occur with?
A
- saturated fatty acid tails
5
Q
phospholipids are mobile in what direction?
A
- horizontal direction, as they can move around relatively freely within a single layer of the bilayer membrane
6
Q
how do phospholipids shift from one side of the membrane to another?
A
- catalyzed using flippases which is energetically costly
7
Q
what are the 3 main classes of lipids present in the p.m.?
A
- phospholipids
- sterols
- glycolipids- cell signalling and cell adhesion (glyceroglycolipid or sphingolipid)
- phospholipids and glycolipids usually contain an even number of C atoms
- unsaturated fatty acids in the bilayer membrane are nearly always found in the cis orientation
8
Q
what are the 3 main classes of membrane proteins?
A
- transmembrane (integral)
- peripheral
- lipid anchored
9
Q
what is the function of integral proteins?
A
- includes membrane-spanning proteins with a hydrophilic cytosolic domain that interacts with the interior of the cell and a hydrophobic membrane-spanning domain that anchors into the cell membrane and a hydrophilic extracellular domain that interacts with the extracellular environment
- common and important class with examples like proton pumps, ion channels, and GPCR
10
Q
what is the function of peripheral proteins?
A
- these proteins are transiently attached to integral membrane proteins or are associated with peripheral regions of the lipid bilayer
- they tend to interact with the biological membrane only transiently before resuming their function within the cytoplasm. this category includes some enzymes and hormones
11
Q
what is the function of lipid-anchored proteins?
A
- they are covalently bound to single or multiple lipid molecules that anchor the protein within the membrane without the protein contacting the membrane
- ex. G proteins which are intracellular membrane bound structures that help coordinate the signaling cascade initiated by GPCR
12
Q
for proteins destined for insertion or association with the p.m. what happens?
A
- an N terminus signal sequence directs the newly synthesized proteins to the ER where they are inserted into the lipid bilayer.
- once inserted, the proteins are then transported to their final destination in vessicles, which eventually fuse with the target membrane
13
Q
proteins can be glycosylated which refers to?
A
- the addition of oligosaccharide chains to a peptide chain
- most common example are O-glycosylation, in which a glycosidic bond is formed to the O atom present in serine and threonine side chains or N-glycosylation in which the oligosaccharide binds to a N on the side chain of asparagine
- ABO blood type system so membrane glycoproteins often involved in cell recognition and communication processes
- most common example are O-glycosylation, in which a glycosidic bond is formed to the O atom present in serine and threonine side chains or N-glycosylation in which the oligosaccharide binds to a N on the side chain of asparagine
14
Q
what is a liposome?
A
- a lipid bilayers enclosing a spherical space used in labs for research
15
Q
what is a micelle?
A
- an aggregate composed of a single layer of lipids in an aqueous solution, where the hydrophilic head region is in contact with the solvent, while the hydrophobic tail region is sequestered in the center of the micelle
19
Q
what is Osmosis?
A
- special form of simple diffusion that only applies to solvents (water)
- osmosis takes place when you have a physical setup in which water can diffuse through a barrier but solutes cannot
27
Q
what is the function of the sodium/potassium pump?
A
- this enzyme helps to maintain the cell potential across membranes by exchanging Na+ for K+ across a membrane, moving both ions against the transmembrane concentration gradients established by the pump
- for every ATP hydrolyzed, 3 Na+ ions are transported out of the cell and 2 K+ ions are transported in. this helps maintain the charge imbalance between the exterior and interior of the cell
29
Q
what are antiporters and symporters?
A
- Symporters and antiporters are involved in active transport.
- Antiporters transport molecules in opposite directions
- symporters transport molecules in the same direction.
30
Q
what is endocytosis?
A
- an energy-using process by which cells absorb molecules by engulfing them
- pinocytosis- cells engluf liquid substances
- phagocytosis- cells engulf solid particles (debris, microorganisms, other apoptotic cells)
- clathrin-mediated endocytisis which involves small vesicles that have a coat composed mainly of cytosolic protein clathrin. clathrin-coated cesicles are found in nearly all cells and form domains in the p.ml termed clathrin-coated pits concentrate large extracellular molecules that are receptor-specific for the endocytosis of their ligands (uptake of LDL, growth factors, antibodies, etc.)
