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15 Cards in this Set

  • Front
  • Back
Some enzyme-catalyzed reactions cease completely if their enzyme is absent.
False- because enzymes enhance the rate but do not change the equilibrium point of a reaction, a reaction will always occur in the absence of the enzyme, though often at a minuscule rate. Moreover, competing reactions may use up the substrate more quickly, thus further impeding the desired reaction. Thus, in practical terms, without an enzyme, some reactions may never occur to an appreciable extent.
High-energy electrons (such as those found in the activated carriers NADH and NADPH) move faster around the atomic nucleus.
False. High-energy electrons are more easily transferred, i.e., more loosely bound to the donor molecule. This does not mean that they move any faster
ATP hydrolysis to form AMP can provide almost twice the energy of ATP hydrolysis to form ADP.
True. Hydrolysis of an ATP molecule to form AMP also produces a pyrophosphate (PPi) molecule, which in turn is hydrolyzed into two phosphate molecules. This second reaction releases almost the same amount of energy as the initial hydrolysis of ATP, thereby approximately doubling the energy yield.
A partially oxidized carbon atom has a smaller diameter than a more reduced one.
True. Oxidation is the removal of electrons, which reduces the diameter of the carbon atom.
Some activated carrier molecules can transfer energy and chemical groups
True. ATP, for example, can donate both energy and /or a phosphate group.
The rule that oxidations release energy, whereas reductions require energy input, applies to all chemical reactions, not just those that occur in living cells.
False. Living cells have selected a particular kind of chemistry in which most oxidations are energy-releasing events; under different conditions, however, such as in a hydrogen-containing atmosphere, reductions would be energy-releasing events.
Cold-blooded animals have an energetic disadvantage because they give less heat to the environment than warm-blooded animals do. This slows their ability to make ordered macromolecules.
False. All cells, including those of cold- and warm-blooded animals, radiate comparable amounts of heat as a consequence of their metabolic reactions. For bacterial cells, for example, this becomes apparent when a compost pile heats up
Linking the reaction X---> Y to a second, energetically favorable reaction Y---> Z will shift the equilibrium constant of the first reaction.
False. The equilibrium constant of the reaction X <-----> Y remains unchanged. If Y is removed by a second reaction, more X is converted to Y so that the ratio of X to Y remains constant.
The active site of an enzyme usually occupies only a small fraction of its surface
True. Only a few amino acid side chains contribute to the active site. The rest of the protein is required to maintain the polypeptide chain in the correct position, provide additional binding sites for regulatory purposes, and localize the protein in the cell.
Catalysis by some enzymes involves the formation of a covalent bond between an amino acid side chain and a substrate molecule
True. Some enzymes form covalent intermediates with their substrates; however, in all cases the enzyme is restored to its original structure after the reaction.
Alpha and Beta sheet can contain up to five strands, but no more
False.  sheets can, in principle, contain any number of strands because the two strands that form the rims of the sheet are available for hydrogen-bonding to other strands, ( sheets in known proteins contain from 2 to 16 strands.)
The specificity of an antibody molecule is contained exclusively in loops on the surface of the folded light-chain domain.
False. It is true that the specificity of an antibody molecule is exclusively contained in loops on its surface; however, these loops are contributed by both the folded light- and heavy-chain domains.
Allosteric enzymes have two or more binding sites
True. Allosteric enzymes generally bind one or more molecules that function as regulators at sites that are distinct from the active site.
The possible linear arrangements of amino acids are so vast that new proteins almost never evolve by alteration of old ones
False. The possible linear arrangements of amino acids that lead to a stably folded protein domain are so few that most new proteins evolve by alteration of old ones
Noncovalent bonds are too weak to influence the three-dimensional structure of macromolecules.
False. Noncovalent bonds are a major contributor to the three-dimensional structure of macromolecules.