Exam 2 Flashcards
Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?
A.) Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient.
B.) Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.
C.) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose
D.) Sodium and glucose compete for the same binding site in the cotransporter.
C.) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose
A sodium-potassium pump _____.
A.) move three sodium ions out of a cell and two potassium ions into a cell while consuming an ATP for each cycle
B.) move three sodium ions out of a cell and two potassium ions into a cell and generates an ATP in each cycle
C.) moves three potassium ions out of a cell and two sodium ions into a cell while consuming 2 ATP in each cycle
D.) moves three potassium ions out of a cell and two sodium ions into a cell while producing an ATP for each cycle
A.) move three sodium ions out of a cell and two potassium ions into a cell while consuming an ATP for each cycle
The force driving simple diffusion is _____, while the energy source for active transport is _____.
A.) the concentration gradient; ATP
B.) phosphorylated protein carriers; ATP
C.) transmembrane pumps; electron transport
D.) the concentration gradient; ADP
A.) the concentration gradient; ATP
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep a membrane more fluid at lower temperatures?
A.) The double bonds block interaction among the hydrophilic head groups of the lipids.
B.) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
C.) Unsaturated fatty acids are more polar than saturated fatty acids.
D.) Unsaturated fatty acids have a higher cholesterol content and, therefore, more cholesterol in membranes.
B.) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At higher temperatures, these regions _____.
A.) have higher rates of lateral diffusion of lipids and proteins into and out of these regions
B.) detach from the plasma membrane and clog arteries
C.) are more fluid than the surrounding membrane
D.) are less fluid than the surrounding membrane
D.) are less fluid than the surrounding membrane
The voltage across a membrane is called the \_\_\_\_\_. A.) membrane potential B.) chemical gradient C.) osmotic potential D.) electrochemical gradient
A.) membrane potential
Which of these are NOT embedded in the hydrophobic portion of the lipid bilayer at all?
A.) transmembrane proteins
B.) integral proteins
C.) All of these are embedded in the hydrophobic portion of the lipid bilayer.
D.) peripheral proteins
D.) peripheral proteins
What kinds of molecules pass through a cell membrane most easily? A.)small and hydrophobic B.) ionic C.) large and hydrophobic D.) large polar
A.)small and hydrophobic
Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane’s asymmetrical nature?
A.)Since the cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium, the membrane must be asymmetrical
B.) Proteins only function on the cytoplasmic side of the cell membrane, which results in the membrane’s asymmetrical nature.
C.) Since cell membranes communicate signals from one organism to another, the cell membranes must be asymmetrical.
D.) The two sides of a cell membrane face different environments and carry out different functions.
D.) The two sides of a cell membrane face different environments and carry out different functions.
Which of the following most accurately describes selective permeability?
A.) An input of energy is required for transport.
B.) There must be a concentration gradient for molecules to pass through a membrane.
C.) Only certain molecules can cross a cell membrane.
D.) Lipid-soluble molecules pass through a membrane.
C.) Only certain molecules can cross a cell membrane.
Ions diffuse across membranes through specific ion channels down \_\_\_\_\_. A.) the electrical gradients B.) their concentration gradients C.) their electrochemical gradients D.) their chemical gradients
C.) their electrochemical gradients
Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?
A.)Cells of each domain evolved proton pumps independently when oceans became more acidic.
B.) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
C.) Proton pumps are necessary to all cell membranes.
D.) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism.
B.) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
Lysosomes maintain a pH of approximately 4.5-4.7, which is more acidic than the cytosol of the cell. Which of these is most likely responsible for maintaining the low pH of lysosomes?
A.) osmosis
B.) a proton pump that pumps H+ into the lysosome
C.) passive diffusion
D.) a proton pump that pumps H+ out of the lysosome
B.) a proton pump that pumps H+ into the lysosome
White blood cells engulf bacteria using \_\_\_\_\_. A.) receptor-mediated exocytosis B.) osmosis C.) passive diffusion D.) phagocytosis
D.) phagocytosis
Why are lipids and proteins free to move laterally in membranes?
A.) Lipids and proteins repulse each other in the membrane.
B.) There are only weak hydrophobic interactions in the interior of the membrane.
C.) The interior of the membrane is filled with liquid water.
D.) Hydrophilic portions of the lipids are in the interior of the membrane.
B.) There are only weak hydrophobic interactions in the interior of the membrane.
The sodium-potassium pump is called an electrogenic pump because it _____.
A.) is used to drive the transport of other molecules against a concentration gradient
B.) pumps equal quantities of Na+ and K+ across the membrane
C.) contributes to the membrane potential
D.) ionizes sodium and potassium atoms
C.) contributes to the membrane potential
For a protein to be an integral membrane protein, it would have to be _____.
A.)hydrophobic
B.) hydrophilic
C.) amphipathic, with at least one hydrophobic region
D.) exposed on only one surface of the membrane
C.) amphipathic, with at least one hydrophobic region
Which of the following would increase the electrochemical gradient across a membrane?
A.) both a proton pump and a potassium channel
B.) a potassium channel
C.) a sucrose-proton cotransporter
D.) a proton pump
D.) a proton pump
Which of the following membrane activities requires energy from ATP?
A.) movement of carbon dioxide out of a paramecium
B.) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell
C.) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
D.) facilitated diffusion of chloride ions across the membrane through a chloride channel
C.) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
Which of the following is true of osmosis?
A.) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.
B.) Osmosis is an energy-demanding or “active” process.
C.) In osmosis, solutes move across a membrane from areas of lower water concentration to areas of higher water concentration.
D.) Osmosis only takes place in red blood cells.
A.) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.
In the process of transcription, \_\_\_\_\_. A.) RNA is synthesized B.) proteins are synthesized C.) mRNA attaches to ribosomes D.) DNA is replicated
A.) RNA is synthesized
The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?
A.) DNA was the first genetic material.
B.) A gene from an organism can theoretically be expressed by any other organism.
C.) Different organisms have different types of amino acids.
D.) The same codons in different organisms translate into different amino acids.
B.) A gene from an organism can theoretically be expressed by any other organism.
In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein? A.) primase B.) RNA polymerase I C.) RNA polymerase III D.) RNA polymerase II
D.) RNA polymerase II
Once researchers identified DNA as the unit of inheritance, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. What is the mechanism of information transfer in eukarotes?
A.) Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.
B.) DNA from a single gene is replicated and transferred to the cytoplasm, where it serves as a template for protein synthesis.
C.) Proteins transfer information from the nucleus to the ribosome, where protein synthesis takes place.
D.) Transfer RNA takes information from DNA directly to a ribosome, where protein synthesis takes place.
A.) Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.
