5 Membrane Transport and Cell Signaling Flashcards
Which of the following types of molecules are the major structural components of the cell membrane?
phospholipids and proteins
Singer and Nicolson’s fluid mosaic model of the membrane proposed that
membranes consist of protein molecules embedded in a fluid bilayer of phospholipids.
The presence of cholesterol in the plasma membranes of some animals
enables the membrane to stay fluid more easily when cell temperature drops.
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.
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 order for a protein to be an integral membrane protein it would have to be
amphipathic, with at least one hydrophobic region.
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.
Which of the following is true of integral membrane proteins?
They are usually transmembrane proteins.
The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is
to mediate cell-to-cell recognition.
A protein that spans the phospholipid bilayer one or more times is
a transmembrane protein.
Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all? A) transmembrane proteins B) integral proteins C) peripheral proteins D) integrins E) glycoproteins
peripheral proteins
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
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.
Nitrous oxide gas molecules diffusing across a cell’s plasma membrane is an example of
diffusion across the lipid bilayer.
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.
Water passes quickly through cell membranes because
it moves through aquaporins in the membrane.
Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater?
Water will leave the cells, causing them to shrivel and collapse.
Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?
The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur?
The cell will become turgid.
Which of the following membrane activities require energy from ATP hydrolysis?
Na+ ions moving out of a mammalian cell bathed in physiological saline
Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?
facilitated diffusion
What is the voltage across a membrane called?
membrane potential
The sodium-potassium pump is called an electrogenic pump because it
contributes to the membrane potential.
The movement of potassium into an animal cell requires
an energy source such as ATP.
Ions diffuse across membranes through specific ion channels
down their electrochemical gradients.
Which of the following would increase the electrochemical potential across a membrane?
a proton pump
The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?
It will be on the cytoplasmic side of the ER.
An organism with a cell wall would most likely be unable to take in materials through
phagocytosis.
White blood cells engulf bacteria through what process?
phagocytosis
The difference between pinocytosis and receptor-mediated endocytosis is that
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?
on the inside surface of the vesicle
A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in
lysosomes.
What role does a transcription factor play in a signal transduction pathway?
By binding to DNA it triggers the transcription of a specific gene.
Which of the following is a substance that acts at a long distance from the site at which it is secreted?
hormone
To what does the term “ligand” refer in cell biology?
any small molecule that can bind in a specific manner to a larger one
Why are there often so many steps between the original signal event and the cell’s response?
Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.
Active and passive transport of solutes across a membrane typically differ in which of the following ways?
Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy.
Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because __________.
they amplify the original signal manyfold
