Exam 2
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What are the roles of the cell membrane in a cell’s daily activities for survival and function?
-protection -encloses inside of cell from outside environment -regulate transport of substances inside and out of the cell -receives chemical messages from other cells -cell mobility
What do “fluid” and “mosaic” refer to in the fluid-mosaic model of the cell membrane?
Fluid = due to flexibility and lateral movement of the membrane Mosaic = the array of proteins, lipids, and macromolecules present in the membrane
What supports the current fluid-mosaic model?
Freeze-fracture technique Electron microscopy Human and Mouse cell mixed proteins
How might the membrane of an epithelial cell in the intestines be different than the membrane of a neuron?
Epithelial: may be more permeable, contain greater proteins in absorption, such as aquaporins, glucose, ions, lipids, etc. Neuron: have more of a focus on sodium channels, especially voltage-gated sodium channels to aid in the generation of an action potential
Why is a liposome energetically favorable?
maximizes hydrogen bonding and nonpolar interactions
If a drug was added to a cell that inhibited scramblase activity, what is expected to happen?
the phospholipid bilayer would grow asymmetrically, with more lipids on the cytosolic side of the ER membrane
What allows a “flip-flop” to occur more easily in a cell membrane?
Flippases
In what way do water molecules organize themselves?
in a way to maximize hydrogen bonding between the hydrogen of one and the oxygen of another
Why do membrane lipids form bilayers in water?
they are amphipathic
Where does membrane synthesis occur?
ER
What are two ways in which the cytosolic monolayer is different from the non-cytosolic monolayer?
glycolipids on exterior surface - these don’t get flipped specific phospholipids are flipped to the cytosolic side, while some remain on exterior surface
What is a flippase?
proteins that aid in “flipping” specific phospholipids to cytosolic monolayer
What are Glycolipids and an example of a function in a membrane?
Lipid + Carb adhesion, cell signaling, identification Act as receptors on the surface of RBCs (help determine blood group)
Why is non-cystolic a better term than exterior?
gets confusing in the case of a vesicle that leaves from a membrane-bound organelle, where the “exterior” is really the cytosolic face (as it is facing the cytosol of the cell)
TRUE OR FALSE: Phosphatidylserine is normally found in the extracellular face of the cell membrane
FALSE - it is normally found in the intracellular face (cytosolic face)
Why do cells need fluid membranes?
so they can adjust fluidity at different temperatures (not be stuck and unable to move)
What helps keep membranes fluid and why?
Unsaturated fatty acids cholesterol - for more structure holds together lipids at high temps acts to spread out lipids at low temps, keeping them from solidifying
How do organisms change their membrane composition to match environmental temperatures to keep membrane fluid?
changes in fatty acid composition (unsaturated = more fluid in lower temps, saturated = viscous in higher temps cholesterol provides greater structure and acts as a “temperature buffer”
How do the properties of lipids, and the lipid composition of the membrane, influence membrane fluidity?
Saturated fatty acid = more rigid, less fluid Longer fatty acid chains = more rigid, less fluid membrane proteins = can promote clustering of lipids or disrupt it (increasing fluidity)
Give a biological example of when a cell would benefit from changing its membrane fluidity
If temperatures drop, cholesterol and unsaturated hydrocarbon tails allow for the membrane to stay fluid and not become “stuck” because of the lower temperature (and unable to move) e.g. antifreeze protein properties in fish
Name examples of lipids and what they have in common
Phospholipids Triglycerides Glycolipids Steroids In Common: energy storage, transport, communication, nonpolar
When will a protein associate with the membrane?
At the region where protein is nonpolar
What structure provides structural stability and strength to a cell membrane?
Cell Cortex (actin network)
What is a human disease that results from a problem with proteins in the cell cortex?
Hereditary elliptocytosis