Plasma Membrane and Neuronal Communication
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The major component of cell membranes is
a lipid bilayer
Membranes contain a wide diversity of lipids, including
cholesterol, phosphoglycerides and sphingolipids
What is true about the cholesterol associated with membranes?
It interferes with the movements of the fatty acid tails of the phospholipids.
Proteins that penetrate the lipid bilayer
may pass entirely through the lipid bilayer and protrude from both the extracellular and cytoplasmic sides of the membrane.
What allows membranes to be permeable to small ions?
ion channels
What does Facilitated diffusion do
allows substances to diffuse through a membrane by binding to a facilitative transporter.
Active transport
requires coupling to an energy-releasing system and depends on integral membrane proteins to move solutes across a membrane.
Myelination is associated with
prevention of passage of ions across the plasma membrane and higher speeds of conduction of impulses along axons.
You are studying a transport molecule. It appears to bind temporarily to the molecule to be transported. During normal transport, no energy is expended. What kind of transport is described?
This is an example of facilitated diffusion.
You are exploring a rather inhospitable planet, which has seas that are somewhat hydrophobic in nature. Surprisingly, there are living organisms in the seas whose cytoplasm is hydrophobic to a similar degree. These organisms have membranes made primarily of phospholipids arranged in a bilayer. What is the most probable orientation of these phospholipids?
The polar heads of the phospholipids face toward the middle of the bilayer with the hydrophobic fatty acid tails facing outward.
A molecule normally enters a cell by simple diffusion through the lipid bilayer. What happens if you artificially reverse the molecule’s concentration gradient?
The molecule moves out of the cell.
Why are molecules that block oxidative phosphorylation and the electron transfer chain such dangerous and potentially deadly poisons?
Upon blocking the electron transport chain, the electron transport chain backs up and little or no ATP will be made. Consequently, the organism will die.
Why do your muscles hurt for some time after a large amount of anaerobic exercise?
If your muscles have been running anaerobically, they will produce lactic acid as a byproduct of fermentation. The buildup of lactic acid can lower the pH of muscle tissue from 7.0 to 6.35. This may lead to the pain and cramps that can accompany vigorous exercise.
Observations of two different cell types indicate a couple of differences in their mitochondria. The mitochondria in Cell Type 1 are larger, contain more cristae and the cristae extend farther across the mitochondria than in Cell Type 2. Which cell type is likely to have more extensive energy requirements?
Since ATP synthase is located on the cristae, cells that have more cristae with a larger surface area will be able to make more ATP to satisfy those energy requirements. Consequently, Cell Type 1 probably has the largest energy requirements.
In the middle of the winter, the membranes from a tissue sample from an organism dwelling in a pond are analyzed for their phospholipid content. In the middle of the summer, another tissue sample is taken from the same type of organism and the membrane lipid content determined. Has the lipid content changed? How has it changed and why?
Yes, the lipid composition has changed. The lipids have become more saturated in the warmer environment. Saturated fatty acids can pack more tightly, making the membrane more solid at higher temperatures.