KA FC 2: Cell Membrane questions

Longer and more saturated fatty acids have what effect on the fluidity of cell membranes?

-At high temperatures, it decreases cell membrane fluidity -Longer FA tails increase SA of Van der Waals interactions

Which molecule diffuses thru the cell membrane most quickly? A) Urea B) Ethylene C) Glucose D) Benzene

B) Ethylene -Ethylene (C2H4), is the smallest & a non-polar molecule-diffuses thru membrane most quickly compared to larger & polar molecules

Which statement best describes how cholesterol affects cell membrane fluidity? A) Decreases fluidity @ low temps, increases fluidity @ high temps B) Increases fluidity @ low temps, decreases fluidity @ high temps C) Decreases fluidity @ low temps, decreases fluidity @ high temps D) Increases fluidity @ low temps, increases fluidity @ high temps

B) Increases fluidity @ low temps, decreases fluidity @ high temps -The fluidity of cell membranes is determined in large part by how well the fatty acid tails of phospholipids can interact with each other via Van der Waals forces. The closer fatty acids can pack together the LESS fluid the membrane becomes. -At high temperatures, phospholipids are already fairly well-separated from each other. Cholesterol fills in these gaps, pulling phospholipids closer together & increases strength of Van der Waals forces among fatty acid tails. -Cholesterol decreases fluidity at high temperatures (due to increased Van der Waals forces) and increases fluidity at low temperatures (due to decreased Van der Waals forces).

Which intermolecular process primarily derives the formation of a bilayer when phospholipids are added to H2O? A) A bilayer arrangement maximizes the strength of Van Der Waals forces among phospholipids B) Ordered arrangement of bilayer is more favorable than the disordered state of individual free-floating phospholipids C) Lipids cause H2O to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect. D) Phospholipids self-assemble into a bilayer due to their strong affinity they have for one another

C) Lipids cause H2O to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect. -The formation of a phospholipid bilayer is primarily driven by an increase in entropy of surrounding H2O molecules. Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect, thus increasing entropy. -Systems tend towards increased entropy. A disordered state is MORE favorable than an ordered state. -The formation of a phospholipid bilayer is primarily driven by an increase in entropy of surrounding water molecules. Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect, thus increasing entropy.

Compared to a typical animal cell, the cell membranes on the paw of a polar bear would most likely have an increased concentration of which macromolecule? A) K+ channel proteins B) Saturated phospholipids C) Unstaurated phospholipids D) Aquaporin proteins

C) Unsaturated phospholipids -Paws need to be able to remain fluid to tolerate low temps. -For a cell to function @ low temps, it must increase membrane fluidity -Membrane fluidity increases with increased presence of unsaturated phospholipids

Glucose enters the cell thru which mechanism? A) Pinocytosis thru cell membrane B) Simple diffusion thru cell membrane C) Active transport by glucose carrier protein D) Facilitated diffusion thru carrier protein

D) Facilitated diffusion thru carrier protein

Rate of osmosis of a cell depends on which of the following? I. Intracellular solute conc. II. Extracellular solute conc. III. Polarity of molecules IV. MW of solutes V. Presence of aquaporins A) I, III & IV B) I, II, III, IV & V C) I & II D) I, II, V

D) I, II, V -Omsotic pressure = collagative property-depends ONLY on solute/solvent ratio, NOT on identity of solute/solvent -Polarity & MW of solutes don't affect osmosis -Aquaporins transport H2O across the membrane

Which type of cell membrane protein is likely to be a hormone? A) Integral protein B) Steroid C) Lipid-bound protein D) Peripheral protein

D) Peripheral protein -Steroids ≠ membrane proteins -Integral proteins can't easily leave the cell membrane => is a poor signaling molecule -Lipid-bound proteins can't leave the membrane => poor signalig molecules -Peptide hormones like insulin & growth hormones interact w/ integral protein receptors in cell membranes. They can be considered peripheral membrane proteins

In nerve cells, the Na-K pump exchanges 2 K+ for 3 Na+ across the cell membrane. What is th 1º purpose of this? A) To increase the [Na+] inside the cell B) To propagate an AP C) To increase the K+ stored outside the cell D) To store electrical & chemical potential energy

D) To store electrical & chemical potential energy -During an AP, Na+ & K+ ions move across the membrane thru Na-K channels, NOT pumps -The pumps increase [Na+] outside & increase [K+] inside -They create an electrochemical grad. b/w the inside & outside of the cell-produces electrical & chemical energy to be used in AP's

Which statement represents a notable different between simple diff'n & faciliated diff'n? A) Unlike simple diff'n, facilitated diff'n can transport ligands against a conc. grad. B) Unlike simple diff'n, facilitated diff'n requires energy in the form of ATP C) Unlike simple diff'n, facilitated diff'n can occur in any type of cell D) Unlike simple diff'n, the rate of facilitated diff'n is limited by the # of transport proteins in the cell

D) Unlike simple diff'n, the rate of facilitated diff'n is limited by the # of transport proteins in the cell