BIO 1140 Lecture Notes - Lecture 6: Prenylation, Channel Tunnel, Cell Membrane

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Recall:
Both layers are different because they interact with different environments… different
functions interior vs exterior
oCellular recognition outer layer
oInteractions with cytoskeleton inner layer
Membrane Fluidity
How is it maintained?
Different changes influence how fluid the membrane is: temperature, chain length,
saturation, polarity
Higher temperature = higher excitement, more movement and more fluid
Lower temperature = less excitement, less vibrations, more interactions between fatty
acid tails, more compacted, less fluidity
Unsaturated bonds = kinks/changes in the structure/influences how tightly packed the
fatty acids are
oThink in areas and not overall membrane
Length of the chains…
Cholesterol fills in the space in between the phospholipids – changes how tightly packed
the phospholipids are
oCholesterol also influenced by temperature; maintain fluidity at BOTH EXTREME
TEMPERATURES
oLow  phospholipids very compact – introducing cholesterol increases the spaces
in between phospholipids – spaces them out
oHigh  phospholipids less compact – cholesterol restrict the movement of
phospholipids – compact them
oThat’s why sterols are called BUFFERS – even out at both high and low
temperatures
oBuffer effect going on with the cholesterol
Polarity affects fluidity – different types of phospholipids along the membrane
oFour main types of phospholipids with different functional groups  different
polarities
oPolarities of the phospholipids influences how fluid the membranes are at those
points
The membrane adapts to the environment to maintain membrane fluidity.
Homeoviscous adaptation: the compositional adaptation of membrane lipids that serves
to maintain the correct membrane fluidity at the new conditions.
Membrane is fluid at its optimal level – then the fish tanks are switched
Fish’s membranes react to adjust to the new environments
Adjust composition of their membranes to regain optimal fluidity
oBecome more/less compact depending on changes encountered
oLike homeostasis
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oGoal is to get a membrane that is optimally fluid
Q. Terrence the trout is caught from his pond, which is a nice 28˚C, and then transferred to a
chilly holding container at 10˚C. Terry’s cells will respond initially to the change in temperature
but then will adjust. The membranes will need to become more _____, cholesterol will _____,
and PC/PE ratio will _____.
PE IS MORE POLAR THAN PC
Want more PE because it’s more polar, to increase fluidity
Less PC more PE
Since PE’s more polar
A. Rigid, decrease, decrease
B. fluid, decrease, increase
C. rigid, increase, decrease
D. fluid, increase, decrease
Why are there proteins in the plasma membrane?
Proteins play a key role in:
1. transport
2. enzymes (catalytic activity)
3. signal transduction
4. attachment/recognition
MEMBRANE PROTEINS (3)
Integral proteins = transmembrane proteins
within; BOUND to the membrane
span the entire membrane
a portion of the protein interacts with both interior and exterior
form a hydrophilic core – makes a passage for polar molecules to pass through (water)
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