Lecture 4 Nucleotides and nucleic acids Chapter 33

Question 1

What was known about DNA by the 1950s?
a. DNA is composed of four nitrogen bases.
b. The structure of DNA is a double helix.
c. There are certain principles of DNA replication.
d. There are different enzymes that take part in DNA transcription.
e. The stacked bases interact with van der Waals forces.

Answer 1

a. DNA is composed of four nitrogen bases.

Question 2

What are the components of a nucleic acid monomer?
a. a base, an ester residue, a phosphate
b. an amino acid, an ester residue, a base
c. a sugar, a base
d. a sugar, a phosphate, a base
e. an amino acid, a sugar, a phosphate

Answer 2

d. a sugar, a phosphate, a base

Question 3

. Why does RNA have a 2′-hydroxyl group in a sugar while DNA does not?
a. The hydroxyl group of a DNA sugar is broken rapidly in a water solution.
b. The presence of a hydroxyl group is impossible in the negatively charged DNA.
c. The absence of a 2′-hydroxyl group in DNA increases its resistance to hydrolysis.
d. The hydroxyl group of a DNA sugar is absent in order to avoid possible mutations.
e. The oxygen atom of the hydroxyl group is too reactive to be in a hydroxyl form.

Answer 3

c. The absence of a 2′-hydroxyl group in DNA increases its resistance to hydrolysis.

Question 4

Which statements reflect the Watson–Crick model of DNA? Select all that apply.
a. Two helical DNA strands are coiled around a common axis, forming a right-handed double helix.
b. The diameter of the helix is 30 Å.
c. The purine and pyrimidine bases lie outside of the helix.
d. The sugar–phosphate backbone lies outside of the helix.
e. The strands of DNA run in the same direction.

Answer 4

a. Two helical DNA strands are coiled around a common axis, forming a right-handed double helix./ d. The sugar–phosphate backbone lies outside of the helix.

Question 5

Which interactions take part in forming complementary base pairs?
a. ionic bonds
b. covalent bonds
c. hydrogen bonds
d. van der Waals forces
e. base-stacking interactions

Answer 5

c. hydrogen bonds

Question 6

Choose the CORRECT statement about semiconservative replication of DNA.
a. Daughter double-stranded DNA molecules are identical to the corresponding parental ones.
b. One of the strands of each daughter DNA molecule is newly synthesized, whereas the other is passed unchanged from the parent DNA molecule.
c. Each daughter DNA molecule is single-stranded and identical to the parent DNA molecule.
d. Two daughter DNA molecules are double-stranded and differ from the parent.
e. There is one daughter double-stranded DNA molecule, which is identical to the parental one.

Answer 6

b. One of the strands of each daughter DNA molecule is newly synthesized, whereas the other is passed unchanged from the parent DNA molecule.

Question 7

What is the direct consequence of the hydrophobic effect that stabilizes the double helix structure?
a. DNA is insoluble.
b. Sugars become more sensitive to digestion.
c. Phosphodiester bonds are more prone to breaking.
d. DNA is a rigid molecule.
e. Bases are positioned inside the helix.

Answer 7

c. Phosphodiester bonds are more prone to breaking.

Question 8

What bonds connect adjacent sugars in a DNA strand?
a. ionic bonds
b. hydrogen bonds
c. peptide bonds
d. disulfide bridges
e. phosphodiester bonds

Answer 8

c. peptide bonds

Question 9

Which nitrogen atom of a purine and a pyrimidine bases is bound to a 1′-carbon atom of the sugar?
a. N-1 of purine and N-1 of pyrimidine
b. N-1 of purine and N-3 of pyrimidine
c. N-3 of purine and N-9 of pyrimidine
d. N-9 of purine and N-3 of pyrimidine
e. N-9 of purine and N-1 of pyrimidine

Answer 9

c. N-3 of purine and N-9 of pyrimidine

Question 10

Choose the CORRECT fact about RNA.
a. branched polymer consisting of nucleotides A, G, U, C; the sugar is fructose
b. unbranched polymer consisting of nucleotides A, G, C, T; the sugar is deoxyribose
c. unbranched polymer consisting of nucleotides A, G, C, U; the sugar is ribose
d. unbranched polymer consisting of nucleotides A, G, C, U; the sugar is deoxyribose
e. unbranched polymer consisting of nucleotides A, G, C, T; the sugar is glucose

Answer 10

c. unbranched polymer consisting of nucleotides A, G, C, U; the sugar is ribose

Question 11

Choose the techniques that Meselson and Stahl used to establish semiconservative replication of DNA.
a. isotope labeling and density gradient equilibrium sedimentation
b. isotope labeling and photoaffinity labeling
c. DNA sequencing and photoaffinity labeling
d. density gradient equilibrium sedimentation and DNA sequencing
e. PCR and stable-isotope probing

Answer 11

a. isotope labeling and density gradient equilibrium sedimentation

Question 12

How is the melting temperature of a double-stranded DNA defined?
a. It’s a temperature at which a double-stranded DNA is denatured to a single-stranded DNA.
b. It’s a temperature at which half of the helical structures are lost.
c. It’s a temperature at which stacking interactions are lost.
d. The temperature is equal to 70ºC.
e. It’s a temperature of the boiling solution.

Answer 12

b. It’s a temperature at which half of the helical structures are lost.

Question 13

What statement about DNA polarity is TRUE?
a. One end of the chain has a free 5′-OH group. The other end of the chain has a free 3′-OH group.
b. One end of the chain has a 5′-OH group attached to a phosphoryl group. The other end of the chain has a free 3′-OH group, which is linked to another nucleotide.
c. One end of the chain has a free 3′-OH group or 3′-OH group attached to a phosphoryl group. The other end of the chain has a free 3′-OH group, which is linked to another nucleotide.
d. One end of the chain has only a free 5′-OH group. The other end of the chain has a free 3′-OH group. Neither is linked to another nucleotide.
e. One end of the chain has a free 5′-OH group or 5′-OH group attached to a phosphoryl group. The other end of the chain has a free 3′-OH group. None is linked to another nucleotide.

Answer 13

e. One end of the chain has a free 5′-OH group or 5′-OH group attached to a phosphoryl group. The other end of the chain has a free 3′-OH group. None is linked to another nucleotide.

Question 14

Choose the CORRECT components of a nucleoside.
a. a pentose sugar bonded with a hexose sugar
b. a base bonded to a sugar and one or more phosphoryl groups
c. a base bonded to a sugar
d. a base bonded to a sugar and an alcohol residue
e. a sugar bonded to a lipid molecule

Answer 14

c. a base bonded to a sugar

Question 15

Choose the temperature that corresponds to DNA annealing.
a. <Tm>Tm
c. =Tm
d. 24ºC
e. 48ºC</Tm>

Answer 15

a. <Tm

Question 17

How many full turns does a linear B-DNA have if its length is 374 bp?
a. 11
b. 110
c. 37
d. 36
e. 35

Answer 17

c. 37

Question 18

Why is negative supercoiling of DNA vital for the cell?
a. Negatively supercoiled DNA is less sensitive to mutagens.
b. DNA is limited by the cell space and has to fit it.
c. Negative supercoiling prepares DNA for the processes requiring separation of DNA strands.
d. While DNA is negatively supercoiled, it does not undergo mutations.
e. Negative supercoiling makes the DNA molecule more stable.

Answer 18

c. Negative supercoiling prepares DNA for the processes requiring separation of DNA strands.

Question 19

19. How many chromosomes does the human genome include?
    a. 22 autosomal chromosomes and 2 sex chromosomes
    b. 22 pairs of autosomal chromosomes and 2 sex chromosomes
    c. 46 pairs of autosomal chromosomes and 2 sex chromosomes
    d. 46 autosomal and 4 sex chromosomes
    e. 23 pairs of autosomal chromosomes and 1 sex chromosome

Answer 19

b. 22 pairs of autosomal chromosomes and 2 sex chromosomes

Question 20

What is the reason for the presence of major and minor grooves in the B-DNA form?
a. Water solution favors the presence of grooves.
b. It is energetically favorable to have such a structure for the DNA molecule.
c. Hydrogen bonds between complementary base pairs have a different length.
d. Glycosidic bonds of a base pair are not diametrically opposite each other.
e. The grooves are essential for the formation of the Z-DNA form.

Answer 20

d. Glycosidic bonds of a base pair are not diametrically opposite each other.

Question 21

What is the name of DNA isomers that have the same nucleotide sequence but a different coiling?
a. topoisomers
b. stereoisomers
c. enantiomers
d. cis-trans isomers
e. structural isomers

Answer 21

a. topoisomers

Question 22

. What was shown by the existence of Z-DNA?
a. DNA is a long molecule.
b. DNA comprises four nitrogen bases.
c. DNA has a double-helix structure.
d. DNA chains are polar.
e. DNA is a flexible molecule.

Answer 22

c. DNA has a double-helix structure.

Question 23

What are the most common forms of DNA present under physiological conditions? Select all that apply.
a. left-handed double helix
b. Z form
c. right-handed double helix
d. A form
e. B form

Answer 23

c. right-handed double helix/ e. B form

Question 24

Amino acid residues that compose the tail of each histone in a nucleosome are:
a. Lys and Ala.
b. Ala and Asn.
c. Lys and Asp.
d. Lys and Arg.
e. Arg and Ala.

Answer 24

d. Lys and Arg.

Question 25

What structure can be formed from a single-stranded DNA or from a single-stranded RNA? Select all that apply.
a. clover leaf
b. double loop
c. helix-turn-helix
d. helix-loop-helix
e. stem-loop

Answer 25

a. clover leaf/ e. stem-loop

Question 26

Choose the CORRECT components of a nucleosome.
a. H2A-H2B dimer, (H3)2(H4)2 tetramer, 200-bp DNA, linker DNA
b. (H2A)2-(H2B)2 tetramer, H3-H4 dimer, 200-bp DNA, linker DNA
c. H2A-H2B dimer, (H3)2(H4)2 tetramer, 145-bp DNA, linker DNA
d. H2A-H2B dimer, H3-H4 dimer, 100 bp DNA, linker DNA
e. H2A-H2B dimer, (H3)2(H4)2 tetramer, 145-bp DNA

Answer 26

a. H2A-H2B dimer, (H3)2(H4)2 tetramer, 200-bp DNA, linker DNA

Question 27

What type of DNA has been discovered in the nuclei of eukaryotic cells only recently?
a. rDNA
b. eccDNA
c. ssDNA
d. mtDNA
e. cpDNA

Answer 27

b. eccDNA

Question 28

What is the role of DNA winding around the nucleosome? Select all that apply.
a. Temporarily, noncoding DNA has to be packed.
b. Histones in nucleosomes are temporary structures and have to be kept together only during DNA replication.
c. It is essential not to let histones disassemble during DNA replication.
d. The formed structure defends histones from bacteria.
e. This DNA is packed by decreasing its linear extent.

Answer 28

a. Temporarily, noncoding DNA has to be packed./ e. This DNA is packed by decreasing its linear extent.

Question 29

What ion assists in stabilization of complexes of nucleic acids?
a. Mg2+
b. Ca2+
c. K+
d. Na+
e. Fe2+

Answer 29

a. Mg2+

Question 30

Which compounds are distinguished from each other by the presence of a methyl group?
a. uracil and cytosine
b. adenine and guanine
c. uracil and thymine
d. pyrimidine and cytosine
e. purine and guanine

Answer 30

c. uracil and thymine

Question 31

Cisplatin is a cancer chemotherapy drug that prevents replication and transcription. How does it work?
a. The platinic atom of cisplatin forms covalent bonds with carbon atoms in deoxyribose.
b. Chloride ligands of cisplatin are displaced by purines on two adjacent bases.
c. The molecule of cisplatin degrades phosphodiester bonds.
d. Hydrogen bonds between DNA chains are degraded by cisplatin.
e. Amino groups of cisplatin are displaced by pyrimidines on two opposite bases.

Answer 31

b. Chloride ligands of cisplatin are displaced by purines on two adjacent bases.

Question 32

. Which statement about DNA is FALSE?
a. DNA has a double-helix structure.
b. DNA is composed of four bases: A, T, G, and C.
c. Nucleosides are the monomeric units of DNA.
d. The strands of DNA run in opposite directions.
e. A-DNA appears when DNA is less hydrated.

Answer 32

c. Nucleosides are the monomeric units of DNA.

Question 33

Explain the presence of DNA grooves in terms of donor–acceptor interactions.
a. The O-4 atom of thymine and the O-6 atom of guanine are located in the major groove and can serve as hydrogen acceptors.
b. In the major groove, N-7 of guanine or adenine is a potential donor.
c. In the minor groove, N-3 of adenine or guanine can serve as a hydrogen donor.
d. In the major groove, the amino group attached to C-2 of guanine can be a hydrogen acceptor.
e. In the minor groove, N-3 of adenine or guanine and O-2 of thymine or cytosine can serve as hydrogen acceptors.

Answer 33

In the minor groove, N-3 of adenine or guanine and O-2 of thymine or cytosine can serve as hydrogen acceptors.

Question 34

What organisms are exposed to serious devastating influence by oxybenzone?
a. human beings
b. reptiles
c. birds
d. corals
e. bacteria

Answer 34

d. corals

Question 35

Which property of DNA makes the molecule appropriate for storing genetic information?
a. length of DNA
b. hydrogen bonds between nitrogen bases of different strands
c. ability to form three different forms
d. presence of A and T nitrogen bases
e. sequence of one strand determines the sequence of the other

Answer 35

e. sequence of one strand determines the sequence of the other

Question 36

How does oxybenzone affect DNA structure?
a. It modifies thymine forming an oxetane derivative.
b. It breaks phosphodiester bonds.
c. It unwinds DNA chains.
d. It forms stem-loop structures of DNA.
e. It modifies deoxyribose forming ribose.

Answer 36

a. It modifies thymine forming an oxetane derivative.

Question 37

What would be the effect of the increased length of the double-stranded DNA on Tm?
a. Tm would be about 0ºC.
b. Tm would not change.
c. Tm would decrease.
d. Tm would increase.
e. It is difficult to predict.

Answer 37

d. Tm would increase.

Question 38

Choose the CORRECT order of compaction of DNA in eukaryotes.
a. DNA → nucleosome → “beads on a string” → fiber → loops → chromosome
b. DNA → fiber → loops → nucleosome → “beads on a string” → chromosome
c. DNA → “beads on a string” → fiber → nucleosome → loops → chromosome
d. DNA → nucleosome → fiber → loops → “beads on a string” → chromosome
e. DNA → nucleosome → loops → fiber → “beads on a string” → chromosome

Answer 38

a. DNA → nucleosome → “beads on a string” → fiber → loops → chromosome

Question 39

Well-defined and complex structures allow _______ and single-stranded DNA to perform a host of functions that the double-stranded DNA molecule cannot.

Answer 39

RNA

Question 40

The difference in RNA bases compared with DNA bases is that RNA contains:
a. A instead of T.
b. U instead of G.
c. U instead of T.
d. A instead of U.
e. C instead of G.

Answer 40

c. U instead of T.

Question 41

What is the actual mode of replication in the cell?
a. conservative
b. random
c. semiconservative
d. N-linked
e. direct

Answer 41

c. semiconservative

Question 42

The shorthand notation pApCpG denotes that:
a. a phosphate is attached to the 5′ end of the adenosine nucleotide unit.
b. a phosphate is attached to the 3′ end of the guanine nucleotide unit.
c. the cytosine nucleotide has a free hydroxyl group.
d. a phosphate is attached to the 5′ end of the adenosine nucleotide unit and the cytosine nucleotide has a free hydroxyl group.
e. the guanosine nucleotide is attached to the 5′ end of the adenosine nucleotide unit.

Answer 42

a. a phosphate is attached to the 5′ end of the adenosine nucleotide unit.

Question 43

a. hydrogen bonds.
b. van der Waals interactions.
c. disulfide bonds.
d. covalent bonds.
e. ionic bonds.

Answer 43

b. van der Waals interactions.

Question 44

After two generations of replication in the Meselson and Stahl experiment, what was the composition of the two bands?
a. One band was all 14N and one band was all 15N.
b. One band was all 14N and one band was half 14N and half 15N.
c. One band was all 15N and one band was half 14N and half 15N.
d. One band was all 14N and one band was one quarter 14N and three quarters 15N.
e. One band was all 15N and one band was one quarter 14N and three quarters 15N.

Answer 44

b. One band was all 14N and one band was half 14N and half 15N.

Question 45

Which property of DNA makes it more stable than RNA in the basic environment?
a. The negative charge of the phosphate on DNA repels the negative charged base.
b. Histones block access to all except a few nucleotides that act as linkers.
c. The 2′ –H in DNA is not reactive, whereas the 2′ –OH of RNA is reactive under basic conditions.
d. DNA precipitates in basic solutions, making it unreactive.
e. RNA forms elaborate structures that are susceptible to alkaline digestion.

Answer 45

c. The 2′ –H in DNA is not reactive, whereas the 2′ –OH of RNA is reactive under basic conditions.

Question 46

What is a transient copy of genetic information?
a. supercoiled RNA
b. DNA
c. B-DNA
d. Z-DNA
e. RNA

Answer 46

e. RNA

Question 47

Which scientist provided data for Watson and Crick’s model of DNA?
a. Francis Collins
b. Barbara McClintock
c. Erwin Chargaff
d. Rosalind Franklin
e. Marcus Rhoades

Answer 47

d. Rosalind Franklin

Question 48

Which form of DNA is possible as well as the linear form?
a. supercoiled
b. circular
c. stem loop
d. B-DNA
e. A-DNA

Answer 48

b. circular

Question 49

Select all that apply. Unwinding prior to ligation results in:
a. a relaxed DNA.
b. a narrowing of a major groove.
c. negative supercoiling.
d. positive supercoiling.
e. restrictase activity.

Answer 49

b. a narrowing of a major groove./ c. negative supercoiling.

Question 50

What is the name of the process of rehybridization of melted DNA?
a. denaturation
b. Tm
c. annealing
d. dehybridization
e. replication

Answer 50

c. annealing