Chapter 5 concept check
Proteins are the most structurally and functionally diverse class of biological molecules. Explain the basis for this diversity.
A polypeptide, which may consist of hundreds of amino acids in a specific sequence (primary structure), has regions of coils and pleats (secondary structure), which are then folded into irregular contortions (tertiary structure) and may be noncovalently associated with other polypeptides (quaternary structure). The linear order of amino acids, with the varying properties of their side chains (R groups), determines what secondary and tertiary structures will form to produce a protein. The resulting unique three-dimensional shapes of proteins are key to their specific and diverse functions.
Compare the structure of a fat (triglyceride) with that of a phospholipid.
Both have a glycerol molecule attached to fatty acids. The glycerol of a fat has three fatty acids attached, whereas the glycerol of a phospholipid is attached to two fatty acids and one phosphate group.
Compare the composition, structure, and function of starch and cellulose. What role do starch and cellulose play in the human body? (5.2)
Both starch and cellulose are polymers of glucose, but the glucose monomers are in the α configuration in starch and the β configuration in cellulose. The glycosidic linkages thus have different properties. Starch is an energy-storage compound in plants; cellulose is a structural component of plant cell walls. Humans can hydrolyze starch to provide energy but cannot hydrolyze cellulose. Cellulose aids in the passage of food through the digestive tract.
A dehydration reaction joins two glucose molecules to form maltose. The formula for glucose is C6H12O6. What is the formula for maltose?
C12H22O11
Write the formula for a monosaccharide that has three carbons.
C3H6O3
Why are human sex hormones considered lipids?
Human sex hormones are steroids, a type of hydrophobic compound.
Why are lipids not considered to be macromolecules for polymers?
Lipids are not polymers because they do not exist as a chain linked monomers. They are not considered macromolecules because they do not reach the giant size of many polysaccharides, proteins, and nucleic acids.
How many molecules of water are needed to completely hydrolyze a polymer that is ten monomers long?
Nine, with one water molecule required to hydrolyze each connected pair of monomers.
What parts of a polypeptide participate in the bonds that hold together secondary structure? Tertiary structure?
Secondary structure involves hydrogen bonds between atoms of the polypeptide backbone. Tertiary structure involves interactions between atoms of the side chains of the amino acid subunits.
What role does complementary base pairing play in the functions of nucleic acids?
The complementary base pairing of the two strands of DNA makes possible the precise replication of DNA every time a cell divides, ensuring that genetic information is faithfully transmitted. In some types of RNA, complementary base pairing enables RNA molecules to assume specific three-dimensional shapes that facilitate diverse functions.
What are the four main classes of large biological molecules? Which class does not consist of polymers?
The four main classes are proteins, carbohydrates, lipids, and nucleic acids. Lipids are not polymers.
Why does a denatured protein no longer function normally?
The function of a protein is a consequence of its specific shape, which is lost when a protein becomes denatured.
What is the fundamental basis for the differences between carbohydrates proteins, and nucleic acids?
The polymers of carbohydrates, proteins, and nucleic acids are built from three different types of monomers: monosaccharides, amino acids, and nucleotides, respectively.
The enzyme amylase can break glycosidic linkages between glucose monomers only if the monomers are in the α form. Which of the following could amylase break down? a. glycogen, starch, and amylopectin b. glycogen and cellulose c. cellulose and chitin d. starch and chitin e. starch, amylopectin, and cellulose
a
The structural level of a protein least affected by a disruption in hydrogen bonding is the a. primary level. b. secondary level. c. tertiary level. d. quaternary level. e. All structural levels are equally affected.
a
Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes? a. The two strands of the double helix would separate. b. The phosphodiester linkages of the polynucleotide backbone would be broken. e. All bases would be separated from dexyribose sugars.
b
Which of the following statements concerning unsaturated fats is true? a. They are more common in animals than in plants. b. They have double bonds in the carbon chains of their fatty acids. c. They generally solidify at room temperature. d. They contain more hydrogen than do saturated fats having the same number of carbon atoms. e. They have fewer fatty acid molecules per fat molecule.
b
The molecular formula for glucose is C6H12O6. What would be the molecular formula for a polymer made by linking ten glucose molecules together by dehydration reactions? a. C60H120O60 b. C6H12O6 c. C60H102051 d. C60H100O50 e. C60H111O51
c
Which of the following categories includes all others in the list? a. monosaccharide b. disaccharide c. starch d. carbohydrate e. polysaccharide
d
Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA? a. 5'-purine-pyrimidine-purine-pyrimidine-3' with 3'-purine-pyrimidine-purine-pyrimidine-5' b. 5'-AGCT-3' with 5'-TCGA-3' c. 5'-GCGC-3' with 5'-TATA-3' d. 5'-GCGC-3 with 5'-GCAT-3' e. All of these pairs are correct.
d