L2

Question 1

phospholipids are…

Answer 1

amphipathic molecules, containing hydrophobic tail (uncharged) and hydrophilic head (charged) regions

Question 2

phospholipid bilayer

Answer 2

50:50 ratio of lipids and proteins

exists as a stable boundary between 2 aqueous compartments

phospholipids spontaneously assemble into a membrane bilayer and freely diffuse laterally, membrane proteins also diffuse laterally

charged parts of lipids (headgroups) and proteins do not easily cross the hydrophobic bilayer

Question 3

physiological roles of membrane proteins

Answer 3

1. transport
2. cell-cell recognition
3. intercellular joining
4. attachment to the cytoskeleton and extracellular matrix (ECM)
5. enzymatic activity
6. signal transduction

Question 4

transmembrane proteins have…(what types of a.a. on membrane and elsewhere)

Answer 4

hydrophobic amino acids on the region spanning the membrane

charged amino acids elsewhere

Question 5

hydrophobic molecule interactionss with water

Answer 5

hydrophobic molecules lack polar functional groups that can interact with water molecules, resulting in a highly ordered cage-like shell of water molecules immediately surrounding the nonpolar molecule

putting a hydrophobic substance in water is thermodynamically unfavorable due to the decreased entropy of water molecules in the cage like shell

Question 6

hydrophobic effect

Answer 6

entropy driven aggregation of nonpolar molecules in aqueous solution that occurs to minimize the ordering of water molecules

drives the formation of membranes an contributes to the folding of proteins

Question 7

membrane consistency depends on chemical nature of lipids (viscous/solid vs flows/fluid)

Answer 7

viscous/solid:
-high in sat fat ( few double bonds allows lipids to pack densely)
-higher H atom content makes more van der Waals forces among H atoms
-less fluidity, higher melting temp

flows/fluid
-high in unsat fat ( many double bonds, creates kinks, limits packing density)
-lower H content makess fewer van der Waals forces
-more fluidity, lower melting temp

Question 8

homeoviscus adaptation

Answer 8

cells can actively regulate membrane fluidity

the E. coli membrane maintains fluidity at low growth temperatures by increasing the amount of unsaturated (bent) fatty acid chains in the phospholipids

Question 9

example of homeoviscus adaptation

Answer 9

Desk is a membrane protein that senses “fluidity”

if it is too ordered (cold), it signals to DesR transcription factor

DesR activates expression of gene encoding Des (phospholipid desaturase)

Question 10

cells actively regulate membrane fluidity

Answer 10

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