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- move two potassium ions and three sodium ions while
- consuming an ATP for each cycle.
GLUT-1 is an example of what?
- a transport protein that facilitates diffusion of a
- large molecule across cell membranes
Which of the following means of transport would most
likely be used for moving a large-sized molecule (like a monosaccharide or an
amino acid) from a low concentration on the outside of a cell to a high
concentration on the inside of a cell?
active transport through a "pump" protein
Some channel proteins change their conformations
(alter their folding) in response to either allosteric binding by a ligand or
the development of a electrochemical gradient along the membrane. These
channels can be characterized as
In the co-transport
example discussed in class, H+ ions are pumped out of the cell against their
concentration gradient at the expense of ATP hydrolysis. H+ molecules are then
brought back into the cell along their concentration gradient in a channel
protein along with sucrose molecules moving against its concentration. This
co-transport system in which both molecules enter the cell is an example of
The term phospholipid can best be described by which
of the following?
- a nonpolar lipid molecule that is made amphipathic by
- the addition of a phosphate
membranes are selectively permeable; in which way are they "selectively
- They allow some things to cross while restricting
In an experiment involving
planar bilayers, a solution of table salt (sodium and chloride ions in water)
is added on the left side of the membrane while pure water is added on the
right side. After 30 minutes the researchers test for the presence of ions on
each side of the membrane. The right side tests negative for ions. What can you
Ions do not diffuse across lipid bilayers.
Which of the following is the best explanation for why
cholesterol decreases the permeability of biological membranes?
- Because cholesterol is amphipathic, it fits in between the
- phospholipids and blocks diffusion through the membrane by increasing
- hydrophobic interactions.
You have a planar bilayer with equal amounts of
saturated and unsaturated phospholipids. After testing the permeability of this
membrane to glucose, you increase the proportion of unsaturated phospholipids
in the bilayer. What will happen to the membrane's permeability to glucose?
Permeability to glucose will decrease.
What will happen to a red blood cell (rbc), which has
an internal ion concentration of about 0.9 percent, if it is placed into a
beaker of pure water (no ions present)?
- The cell would swell because the water in the beaker
- is hypotonic relative to the cytoplasm of the rbc.
The movement of water from a region of low solute
concentration to a region of high solute concentration occurs by the process of
What is the name of the currently accepted model of
membrane structure, and where does it place membrane proteins?
- fluid-mosaic; embedded within the membrane and on the
- surfaces of the membrane.
What will happen to a red
blood cell (rbc), which has an internal ion concentration of about 0.9 percent,
if it is placed into a beaker of water that has an ion concentration of 9.0
- The cell would shrink because the water in the beaker
- is hypertonic relative to the cytoplasm of the rbc.
Which of the following
best describes how gramicidin functions?
It forms a channel in the membrane.
What environmental change is responsible for
activating the hydrolytic enzymes found in the typical lysosome?
- a drop in pH due to the influx
- of H+ ions
Which statement best describes results of an
experiment designed to test whether the protein cystic fibrosis transmembrane
conductance regulator (CFTR) is a chloride channel?
- Electric current flowed only in the presence of CFTR, indicating the
- movement of chloride ions.
Proteins are amphipathic molecules that contain
nonpolar (hydrophobic) amino acids and polar (hydrophilic) amino acids. Where
would you expect to find the hydrophobic and hydrophilic amino acid residues of
a protein that spans a cell membrane?
- The hydrophobic amino acids would be oriented toward the outside of the
- protein and come into contact with the hydrocarbon tails of the phospholipid
- bilayer, whereas the hydrophilic proteins would be more concentrated in the
- protein interior.
What would happen if the
NA+/K+ ATPase we discussed in hydrolyzed ATP resulting in a bound phosphate
allosterically associated with the protein and then developed a mutation in
which the ability to remove the phosphate group was "lost"?
- 1) The Na+/K+ ATPase would be locked in a confirmation with its K+ binding sites
- exposed and would be unable to return to its native confirmation.
- 2) Although the Na+ ions would be released, the K+ ions would remain bound to their binding sites without the release of the phosphate
Where would you most likely find an integral membrane protein?
- spanning the cell membrane,
- with parts of the protein visible from both the inside and the outside of the
to the signal hypothesis, as the ribosome begins to translate a new protein,
the first couple of amino acids translated by the ribosome will end up being bound
by the _______________.
signal recognition particle
There are hundreds, if not thousands, of proteins that are specifically localized to
the cell nucleus. What is likely to be true about transport of these proteins
into the nucleus?
- Proteins specifically localized to the nucleus must have the same or a
- similar nuclear localization signal that directs them to the nucleus.
Margulis's theory of endosymbiosis proposes that ____________ evolved from ___________.
You have a distant cousin, age 4, who is always tired and fatigued and is not able
to play games and sports like other healthy children. He most likely has an
enzyme deficiency or defect associated with which intracellular organelle?
Which of the following
cytoskeletal proteins are important in changing cell shape or location (any
type of cell movement)?
- Actin and myosin are among the cytoskeletal proteins important in
- cell movement.
. A large carbohydrate is
tagged with a fluorescent marker and placed in the extracellular environment
surrounding a eukaryotic cell. The cell ingests the carbohydrate via
endocytosis. Upon viewing the cells with a microscope, which of the following
cellular substructures is likely to be fluorescently labeled?
is a defect associated with a defective cytoskeletal protein in red blood
cells. What do you suspect is one consequence of defective cytoskeletal
proteins in red blood cells?
abnormal cell shape
Which of the following statements would best describe a cell that has an extensive
area of smooth endoplasmic reticulum?
It synthesizes large quantities of lipids.
Which of the following statements represents a major difference between prokaryotic
cells and eukaryotic cells?
- Eukaryotic cells tend to have much more extensive inner membrane systems
- and larger numbers of intracellular organelles than do prokaryotes.
Where are the proteins that will be exported (excreted) from the cell made?
in ribosomes that attach to the endoplasmic reticulum
The formation of a cleavage
furrow in animal cells results from interactions between actin and myosin
proteins. This process occurs at the end of mitosis and is referred to as
Lysosomal fusion and
degradation of damaged organelles is a process called __________________.