BIOCH7
Which of the following is true of the evolution of cell membranes?
All components of membranes evolve in response to natural selection.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
CO2
Who was/were the first to propose that cell membranes are phospholipid bilayers?
E. Gorter and F. Grendel
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
It exhibits a specificity for a particular type of molecule.
The formulation of a model for a structure or for a process serves which of the following purposes?
It functions as a testable hypothesis.
Which of the following statements is correct about diffusion?
It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model?
The concentration of protein molecules is now known to be much higher.
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
Cell membranes are asymmetrical. Which of the following is the most likely explanation?
The two sides of a cell membrane face different environments and carry out different functions.
Why are lipids and proteins free to move laterally in membranes?
There are only weak hydrophobic interactions in the interior of the membrane.
Which of the following is true of integral membrane proteins?
They are usually transmembrane proteins
According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?
They can move laterally along the plane of the membrane.
The cell membranes of Antarctic ice fish might have which of the following adaptations?
a high percentage of polyunsaturated fatty acids
A protein that spans the phospholipid bilayer one or more times is
a transmembrane protein.
In order for a protein to be an integral membrane protein it would have to be
amphipathic, with at least one hydrophobic region.
Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. As a result, these lipid rafts
are more rigid than the surrounding membrane.
Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?
by increasing the percentage of unsaturated phospholipids in the membrane
In a paramecium, cell surface integral membrane proteins are synthesized
by ribosomes bound to the rough endoplasmic reticulum.
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
cell-cell recognition
Nitrous oxide gas molecules diffusing across a cell's plasma membrane is an example of
diffusion across the lipid bilayer.
The presence of cholesterol in the plasma membranes of some animals
enables the membrane to stay fluid more easily when cell temperature drops.
Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are
hypertonic to fresh water but hypotonic to the salt solution.
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are
integral proteins.
Water passes quickly through cell membranes because
it moves through aquaporins in the membrane.
Singer and Nicolson's fluid mosaic model of the membrane proposed that
membranes consist of protein molecules embedded in a fluid bilayer of phospholipids.
Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?
peripheral proteins
Which of the following types of molecules are the major structural components of the cell membrane?
phospholipids and proteins
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that
the hydrophobic interactions that hold the membrane together are weakest at this point.
The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is
to mediate cell-to-cell recognition.
