Chapter 5 Practice Questions
Antibiotics—for example, penicillin—cannot be used to treat viral infections, such as the common cold. Why?
Antibiotics inhibit enzymes that are essential to the survival of bacteria only.
In plant cells, carbon dioxide and water are joined to form carbohydrates. Plant cells can also break down carbohydrates such as glucose, releasing carbon dioxide, water, and energy. No one has ever observed such reactions between water and carbon dioxide outside of living cells. What allows simple molecules to assemble into more complex molecules, and also disassemble, in cells but not in other, nonbiological environments?
Cells couple energy-releasing reactions to energy-requiring reactions.
Cells store energy that they use for work in the _____.
Cells store energy that they use for work in the _____.
Frequently, transplanted organs are rejected by the recipient's body. How is this reaction related to plasma membranes?
Each person has a unique set of carbohydrate chains attached to his or her plasma membranes.
Which statement regarding enzyme function is true?
Excessive salt ions can cause an enzyme to denature.
Macrophages are white blood cells that roam the body searching for invading microbes. Inside macrophage vacuoles these invaders are destroyed. How do the microbes get inside the macrophages?
Microbes are engulfed into the macrophage via phagocytosis.
A pharmaceutical company wishes to focus on an enzyme to develop new medications. What type of study would be of the greatest benefit?
Understanding the enzyme's structure would help pharmaceutical companies design molecules that fit to the binding site and alter activity.
Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must _____.
actively pump water back into their cells to counter its loss due to osmosis
Azidothymidine (AZT) is an antiretroviral drug used in the treatment of HIV. It shares a structural similarity to a nucleotide. What might be the mode of action for this drug?
competitive inhibition
New drugs are being developed to lower levels of circulating cholesterol. A successful drug would be one that _____.
increases the rate of LDL receptor-mediated endocytosis
Light is _____ energy, which is converted by plants into molecules, which possess _____ energy.
kinetic ... chemical
You're on the pilot episode of a new reality show called "The Transport Factor." The host hands you three different amino acids, four different sugars, and two different ions. Then the host shouts, "How many different proteins does the cell need to move these molecules across the plasma membrane using facilitated transport?" Quickly, you correctly respond: _____.
nine
Overall, membranes seem to have a great deal in common, but on closer inspection it is revealed that membranes of different cells have unique properties. What is the primary component of membranes that gives membranes cell-specific properties?
proteins
When placed in a hypotonic environment, where the solute concentration is below that of the cell, a houseplant will _____.
remain standing upright
Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?
the difference in water concentration across a selectively permeable membrane
What controls the direction of a molecule, such as oxygen, involved in passive transport?
the direction of the oxygen concentration gradient
What substance is transported by aquaporins?
water
In an oil-based, nonpolar environment, phospholipids would arrange themselves so that they __________.
would stay together but in a reverse orientation, with their tails projecting outward
Which of the following is an accurate comparison of active transport and facilitated diffusion?
Active transport moves solutes against their concentration gradient; facilitated diffusion moves substances down their concentration gradient.
The hydrolysis of DNA into nucleotides constitutes an exergonic reaction. Yet, DNA is quite stable. Why is this the case?
The activation energy required to initiate this reaction is seldom reached.
The eukaryotic cell has multiple membrane-enclosed compartments. This evolutionary innovation provides what advantage to the cell?
The different membrane-enclosed spaces allow different parts of the cell to perform specific functions.
What happens to the chemical energy that is extracted from molecules by cellular activities but that is not used for cellular work?
The energy contributes to the entropy of the system.
The synthesis of an amino acid follows this pathway: precursor A → intermediate B → amino acid C. Each reaction is catalyzed by a different enzyme. This metabolic pathway is controlled by feedback inhibition with amino acid C inhibiting the conversion of precursor A to intermediate B. Amino acid C acts as a _____ of the first enzyme in the pathway.
noncompetitive inhibitor
In a theoretical world where all things are possible, how could you increase the amount of energy that could be stored in a molecule of ATP?
Increase the negative charge of each phosphate group.
Table sugar, or sucrose, is quite stable, and left on its own at room or even human body temperature, breakdown occurs very slowly. The breakdown of sucrose into the simple sugars fructose and glucose is an exergonic reaction. Sucrase, an enzyme, can increase the reaction rate at least one-million-fold. How does the net amount of energy released during the breakdown of sucrose compare between a spontaneous reaction and one catalyzed by sucrase?
The sucrase-catalyzed reaction releases the same amount of energy as the spontaneous reaction.
