Question
Which feature of model 1 best illustrates how biological information is coded in a DNA molecule?
A. The 5′ and 3′ labels at the ends of each strand
B. The labeling of the hydrogen bonds between base pairs
C. The lines connecting sugars and phosphate groups that represent covalent bonds
D. The linear sequence of the base pairs
▶️Answer/Explanation
Ans: D
The sequence of base pairs in a DNA molecule plays a central role in the coding of biological information.
Question
Different polysaccharides are used by plants for energy storage and structural support. The molecular structures for two common polysaccharides are shown in Figure 1. Starch is used by plants for energy storage, and cellulose provides structural support for cell walls. The monomer used to construct both molecules is glucose.
A study determined the effect of two different digestive enzymes, A and B, on these two polysaccharides. Table 1 presents the data from the study.
Mammals do not produce digestive enzyme B. However, sheep and cattle are two types of mammals that contain microorganisms in their digestive tract that produce enzyme B.
Which of the following statements best describes the different functions of starch and cellulose in plants?
A. The differences in the assembly and organization of the monomers of these two polymers result in different chemical properties.
B. Since starch and cellulose are composed of identical monomers, the cellular environment where they are located controls their function.
C. The monomers of cellulose are connected by covalent bonds, making it idea for structural support.
D. The monomers of starch are connected by ionic bonds, making it ideal for energy storage for plants.
▶️Answer/Explanation
Ans: A
The identical orientations of the glucose monomers in starch create a polysaccharide with alpha bonds that is easy to break down into glucose for energy use. The alternating orientations of the glucose monomers in cellulose create beta bonds that produce a rigid polymer that is difficult to digest for energy use.
Question
A scientist conducted an experiment to find out what type of macromolecule a virus injects into a cell. Using radiolabeled atoms, the
scientist found that phosphorus from the virus entered the cell but sulfur did not. Which of the following molecules would most likely be
injected from this virus into the cell?
(A) carbohydrate
(B) nucleic acid
(C) protein
(D) steroid
▶️Answer/Explanation
Ans:
(B) Nucleic acids contain phosphorus but not sulfur. So if phosphorus
entered the cell but sulfur did not, a nucleic acid was most likely
injected. Choice (A) is incorrect because carbohydrates typically do not
contain phosphorus. Proteins typically contain sulfur but not
phosphorus, so choice (C) is incorrect. Choice (D) is incorrect because
steroids are a type of lipid that do not contain phosphorus
Question
In an aqueous environment like the cytosol, the most stable tertiary protein structures would have hydrophilic amino acids in which part of the protein’s structure?
(A) in the interior of the protein, interacting with water in the cytosol
(B) in the interior of the protein, avoiding water in the cytosol
(C) on the surface of the protein, interacting with water in the cytosol
(D) on the surface of the protein, avoiding water in the cytosol
▶️Answer/Explanation
Ans:
(C) Tertiary protein structures in the cell are most stable when their
hydrophilic amino acids are on the surface of the protein, in contact
with the watery cytosol of the cell. Choices (A) and (B) are incorrect
because hydrophobic amino acids are more likely to be found in the
interior of a protein, away from water in the cytosol. Choice (D) is
incorrect because hydrophilic amino acids would not avoid water; they
would be more stable when interacting with water.