| How does the geometry of polar lipids define formation of micelles, vesicles and membrane bilayer? | Micelles:
Forms in the solution of amphipathic molecules that have larger head than tail
Aggregation occurs when the concentration of molecules is higher than a certain threshold
Individual units are wedge-shaped (cross section of head greater than that of side chain)
Vesicles:
Small bilayers will spontaneously seal into spherical vesicles
Vesicles fuse readily with cell membranes or with each other.
Membrane bilayer:
consists of two leaflets of lipid monolayers
Individual units are cylindrical (cross section of head equals that of side chain)
One leaflet faces the cytoplasm
Another leaflet faces the extracellular space or the inside of membrane- enclosed organelle |
| What are the functions of membranes in live cells? | Define the boundaries of the cell
Allow import and export
Retain metabolites and ions within the cell
Provide compartmentalization within the cell
Sense external signals and transmit information into the cell
Produce and transmit nerve signals
Store energy as a proton gradient
Support synthesis of ATP
Serve as catalyst- concentration of molecules
in 2-D space vs 3-D space. |
| What are the common features of membranes? | Sheet-like flexible structure, 30–100 Å (3–10 nm) thick
• Main structure is composed of two leaflets of lipids (bilayer)
• Form spontaneously in aqueous solution and are stabilized by noncovalent forces, especially hydrophobic effect
• Protein molecules span the lipid bilayer
• Asymmetric
Fluid structures: two-dimensional solution of oriented lipids |
| describe the Fluid Mosaic Model of Membranes, composition, asymmetry? | Proposed in 1972 by Singer and Nicholson (UCSD)
• Lipids form a viscous, two-dimensional solvent into which proteins are inserted and integrated more or less deeply
• Integral proteins are firmly associated with the membrane, often spanning the bilayer
• Peripheral proteins are weakly associated and can be removed easily
– Some are noncovalently attached
– Some are linked to membrane lipids
Integral proteins float in this sea of lipid.
• Two leaflets have different lipid compositions
• Outer leaflet is often more positively charged |
| How does the membrane composition among organelles, tissues, organisms vary? | • Ratio of lipid to protein varies
• Type of phospholipid varies
• Abundance and type of sterols varies
• prokaryotes lack sterols
• Cholesterol predominant in the plasma membrane, virtually
absent in mitochondria
• Galactolipids abundant in plant chloroplasts but almost absent in animals |
| What are the types of functionally distinct proteins associated with membranes? | N |
| 3 types of proteins that distinguished based on how they associate with membranes; understand how experimentally these 3 types can be identified, what forces connect these proteins with lipid bilayer? | Peripheral - released by changes in pH or ionic strength, removal of Ca2+ by a chelating agent, or addition of urea or carbonate
Integral - extractable with detergents; proteins covalently attached to membrane lipids could be extracted with phospholipases
Amphitropic proteins –association with membranes is regulated (found both in membranes and in cytosol). |
| Types of Integral Membrane Proteins and be able to draw them schematically? | Types I and II have a single transmembrane helix; the amino-terminal domain is outside the cell in type I proteins and inside in type II.
Type III proteins have multiple transmembrane helices in a single polypeptide.
In type IV proteins, transmembrane domains of several different polypeptides assemble to form a channel through the membrane.
Type V proteins are held to the bilayer primarily by covalently linked lipids. Type VI proteins have both transmembrane helices and lipid anchors. |
| lipid linked membrane proteins (GPI-anchored proteins; myristoylated farnesylated and palmitoylated proteins) what side of the membrane they attached to, where in the protein lipid is attached? | glycosylated derivatives of phosphatidylinositol (GPIs) GPI-anchored proteins are always on the extracellular face.
Farnesylated and palmitoylated
membrane proteins are found on the
inner face
myristoylated proteins found both inside and outside |
| differences between lateral and transverse membrane diffusion? | Lateral Diffusion
Individual lipids undergo fast lateral diffusion within the leaflet.
Transverse Diffusion
Spontaneous flips from one leaflet to another are rare because the charged head group must transverse the hydrophobic tail region of the membrane. |
| example of asymmetric lipids and enzymes that move them across lipid bilayer? | enzymes—flippases—catalyze transverse diffusion
• Some flippases use energy of ATP to move lipids against the concentration gradient |
| What is FRAP and how was it used Experimentally? | • Fluorescence Recovery After Photobleaching (FRAP) allows us to monitor lateral lipid diffusion by monitoring the rate of fluorescence return .
• the rate of return of lipids, the diffusion coefficient of a lipid in the leaflet can be determined Rates of lateral diffusion are high. |
| What are lipid rafts ? | • Lipid rafts - fraction of the plasma membrane that resists detergent solubilization, which can be up to 50%. 50 nm each draft with a patch containing a few thousand sphingolipids and perhaps 10 to 50 membrane proteins. |
| How do lipid rafts differ from other membranes? | • contain clusters of glycosphingolipids with longer-than-usual tails
• are more ordered
• contain specific doubly or triply acylated proteins
• allow segregation of proteins in the membrane |
| what's the relation ship between caveolaes and lipid rafts? | • They are small invaginations in the plasma membrane When several caveolin dimers are concentrated in a small region (a raft), they force a curvature in the lipid bilayer. |
| What's membrane fusion mechanism? | (1) they recognize each other;
(2) their surfaces become closely apposed, which requires the removal of water molecules normally associated with the polar head groups of lipids;
(3) their bilayer structures become locally disrupted, resulting in fusion of the outer leaflet of each membrane (hemifusion); and
(4) their bilayers fuse to form a single continuous bilayer. The fusion occurring in receptor-mediated endocytosis, or regulated secretion, also requires that
(5) the process is triggered at the appropriate time or in response to a specific signal. |
| What's the function of integrins and cadherins? | • Integrins composed of two transmembrane subunits, α and β. The large extracellular domains of the α and β subunits combine to form a specific binding site for extracellular proteins. Collagen and fibronectin.
• Cadherins are a class of type-1 transmembrane proteins. They forming adherens junctions to bind cells within tissues |
| What are the 6 types of transport? | N |
| What's he difference between active and passive transport? | -Transporters for molecules and ions bind their substrates with high specificity, catalyze transport at rates well below the limits of free diffusion, and are saturable in the same sense as are enzymes: there is some substrate concentration above which further increases will not produce a greater rate of transport.
-Passive transport Channels generally allow transmembrane movement of ions at rates that are orders of magnitude greater than those typical of transporters, approaching the limit of unhindered diffusion (tens of millions of ions per second per channel). Channels typically show some specificity for an ion, but are not saturable with the ion substrate, in contrast to the saturation kinetics seen with transporters. |
| What are the 3 classes of transport systems? | N |
| What's the difference between primary and secondary active transport ? | -In primary active transport, the energy released by ATP hydrolysis drives solute (S1) movement against an electrochemical gradient.
- In secondary active transport, a gradient of ion X (S1) (often Na+) has been established by primary active transport. Movement of X (S1) down its electrochemical gradient now provides the energy to drive cotransport of a second solute (S2) against its electrochemical gradient. |
| What are some examples of transport systems ? | Passive Glucose Transport by GLUT1 and GLUT2 uniporter
-Na*-glucose symporter
-Na*K* ATPase cotransporter
-ATP-binding cassette (ABC) transporters
-Proton driven F-type ATPases |
| What are the three transport systems glucose passage through epithelial cells by combined action? | -Passive Glucose Transport by GLUT1 and GLUT2 uniporter
-Na*-glucose symporter
-Na*K* ATPase cotransporter |
| What’s the formula for energy needed for transport across the membrane potential? | ΔGt = RT ln (C2/C1)+ ZF Δψ
Z is the charge on the ion,
F is the Faraday constant (96,480 J/V · mol),
Δψ is the transmembrane electrical potential (in volts) |
