Quizzes for Test 2

Question 1

In deoxyribonucleotides, the pyrimidines are bound to the 1’ carbon of pentose sugar by a ____________­­ to ____________ of the base.
glycosidic bond; N-1
glycosidic bond; N-9
phosphodiester bond; N-3
glycosidic bond; N-3

Answer 1

glycosidic bond; N-1

Question 2

A deoxyribonucleotide is composed of:

Answer 2

nitrogenous base, a deoxyribose, and a phosphate group.

Question 3

Which of the following bases is not found in RNA?
adenine
guanine
thymine
uracil

Answer 3

thymine

Question 4

Which of the following chemical properties or interactions of purines and pyrimidines does not affect the structure and function of nucleic acids?
planar nature of bases due to resonance
tautomerism of the bases
absorbance of UV light
hydrophobic stacking

Answer 4

absorbance of UV light

Question 5

Which of the following is an interaction that stabilizes the three-dimensional structure of DNA?
tautomerism of the bases
absorbance of UV light
hydrophobic stacking
repulsion between the negatively charged phosphate groups of the DNA backbone

Answer 5

hydrophobic stacking

Question 6

The function of telomeres can be best described as:

attachment sites for the proteins of the kinetochore.

sequences at the ends of the linear eukaryotic chromosome that protect the ends from proteases.

sequences of the eukaryotic chromosome that ensure proper distribution during mitosis.

sequences of the bacterial chromosome that ensure proper distribution during binary fission.

Answer 6

sequences at the ends of the linear eukaryotic chromosome that protect the ends from proteases.

Question 7

DNA is found in all the following except:
mitochondria of animals.
mitochondria of plants.
many eukaryotic viruses.
chloroplasts of plants.

Answer 7

many eukaryotic viruses.

Question 8

The double helix of a relaxed closed-circular DNA molecule has one turn of the double helix per ______________base pairs.
10.2
7.5
8
10.5

Answer 8

10.5

Question 9

If a helical turn is removed from a closed-circular DNA molecule:

only supercoiling will occur.

only strand separation will occur.

supercoiling and/or strand separation will occur.

cruciform DNA will likely form.

Answer 9

supercoiling and/or strand separation will occur.

Question 10

Which of the following is the best evidence that supercoiling is an intrinsic property of double-stranded DNA molecules?

Strand separation during transcription and replication introduces supercoiling.

Purified plasmid DNAs are supercoiled even though all proteins are removed.

When two strands of an entwined rubber band are pulled apart they will twist into supercoils.

Linear fragments of double-stranded DNA are not supercoiled.

Answer 10

Purified plasmid DNAs are supercoiled even though all proteins are removed.

Question 11

Which of the following is true of supercoiling?

The relaxed form of DNA is more stable and is therefore the preferred form in the cell.

Most organisms maintain their DNA in a slightly overwound state in order to enhance strand separation during transcription and replication.

Overwound DNA is in the B form so relaxed DNA has less turns than B-form DNA.

Most organisms maintain their DNA in a slightly underwound state in order to compact their DNA.

Answer 11

Most organisms maintain their DNA in a slightly underwound state in order to compact their DNA.

Question 12

The linking number:

changes when double-stranded DNA is bent or deformed.

increases when single-stranded breaks occur in the DNA.

is the number of times one strand of a closed circular DNA is wound about another.

increases when double-stranded breaks occur in the DNA.

Answer 12

is the number of times one strand of a closed circular DNA is wound about another.

Question 13

A relaxed closed-circular DNA of 5,000 bp would have a linking number of:
500
476
347
490

Answer 13

476

Question 14

Which of the following statements about structural maintenance of chromosomes (SMC) proteins is true?

They have four distinct domains: N, C, and two α-helical coiled-coil domains.

Dimers of SMC proteins are all homodimers having identical subunits.

Dimerization of SMC proteins creates a molecule with two heads and two ATP-binding sites.

The ATP bound by SMC proteins is hydrolyzed before the heads come together in the dimer.

Answer 14

Dimerization of SMC proteins creates a molecule with two heads and two ATP-binding sites.

Question 15

The contacts between the DNA and the histones of the nucleosome are:

mainly between the R groups of the histones and the phosphate backbone of the DNA.

mainly between the conserved histone folds and the bases that are exposed in the major groove of the DNA.

more prevalent in regions of the DNA that have tracts of GC base pairs.

primarily between the DNA and the histone peptide backbone.

Answer 15

mainly between the R groups of the histones and the phosphate backbone of the DNA.

Question 16

Which of the following is not a function of histone H1?

stabilizing nucleosomes
binding to regions undergoing active RNA synthesis

enhancing the repression of transcription by nucleosomes

promoting higher order chromosome structure

Answer 16

binding to regions undergoing active RNA synthesis

Question 17

Condensation of DNA yields the 30 nm filament. This filament:

is the most compact form of eukaryotic DNA.

is moderately condensed DNA, as facilitated by H1 and the N-terminal tails.

is also called the chromosomal scaffold.

includes
tetranucleosomes, each 30 nm in diameter.

Answer 17

is moderately condensed DNA, as facilitated by H1 and the N-terminal tails.

Question 18

A histone modification that attracts other proteins such as a transcription factor is said to be acting:
in cis
in trans
epigenetically
as a remodelling protein

Answer 18

in trans

Question 19

How do modified and unmodified histone subunits become distributed among nucleosomes after replication?

The newly synthesized DNA strand contains unmodified histone subunits, while the old strand retains the modified histones.

Both strands of DNA are repopulated first with a mixture of modified and unmodified H2A histones, followed by mixtures of H2B, H3, and, finally, H4

Both strands of DNA are repopulated first with a mixture of modified and unmodified H2A and H2B histones, followed by mixtures of H3 and finally mixtures of H4

Both strands of DNA retain H3-H4 modified pairs, and then are repopulated with unmodified H3-H4 pairs, followed by modified and unmodified H2A-H2B

Answer 19

Both strands of DNA retain H3-H4 modified pairs, and then are repopulated with unmodified H3-H4 pairs, followed by modified and unmodified H2A-H2B

Question 20

Which of the following is not a correct description of DNA replication in bacteria?

DNA replication is semiconservative.

DNA replication is semidiscontinuous.

DNA replication is dispersive.

DNA replication begins at an origin of replication and proceeds bidirectionally.

Answer 20

DNA replication is dispersive.

Question 21

Multiple models were proposed to explain replication. What experimental approach allowed researchers to distinguish between them?

Cells were pulsed with high specific activity [3H] thymidine to show the direction of DNA synthesis on the chromosome.

Cells infected with T4 bacteriophage were grown in the presence of radioactive nucleotides. When DNA was analyzed in alkaline CsCl gradients, the presence of short DNA fragments indicated that discontinuous replication had occurred.

Bacteria were grown on 15NH4 until the entire DNA contained heavy nitrogen and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.

Bacteria were grown on [3H] thymidine until the entire DNA contained heavy thymidine and then the cells were transferred to normal, light media for one round of replication. The resulting DNA molecules were separated in density gradients and compared to the expected results for each proposed model.

Question 22

How did Meselson and Stahl distinguish between semiconservative and conservative replication in their experiment?

After two rounds of replication, only mixed DNA molecules were present in the gradient.

After one round of replication, only mixed DNA molecules were present in the gradient.

After one round of replication, only heavy DNA molecules were present in the gradient.

After one round of replication, only mixed DNA strands were present in alkaline gradients.

Answer 22

After one round of replication, only mixed DNA molecules were present in the gradient.

Question 23

Each replication fork requires both leading and lagging strand synthesis because

DNA synthesis must be complementary.

DNA polymerases can only synthesize DNA 3’ to 5’.

the DNA templates are antiparallel and yet the DNA polymerases only work in one direction.

the helicase unwinds one strand faster than the other.

Answer 23

the DNA templates are antiparallel and yet the DNA polymerases only work in one direction.

Question 24

Which of the following is not necessary for a DNA polymerase reaction?
template DNA
primer strand
ATP
dNTPs

Answer 24

atp

Question 25

Polymerases also have nuclease activities. Which of the following is not a use for the nuclease activities of DNA polymerase I?

proofreading during synthesis

trimming single-stranded ends

removal of RNA primers

degradation of viral DNAs

Answer 25

degradation of viral DNAs

Question 26

Which of the following E. coli polymerases functions in the replication of the chromosome?
DNA Pol I
DNA Pol II
DNA Pol III
DNA Pol IV

Answer 26

DNA Pol III

Question 27

Pol III holoenzyme of E. coli is composed of:

three Pol III cores, two β clamps, two clamp loaders.

three Pol III cores, two β clamps, one clamp loader.

two Pol III cores, two β clamps, and one clamp loader.

three Pol III cores, four β clamps, one clamp loader.

Answer 27

three Pol III cores, two β clamps, one clamp loader.

Question 28

The function of DNA ligase is to:

catalyze the formation of covalent bonds between adjacent nucleotides.

unwind the double-stranded DNA prior to replication.

keep the single strands of DNA apart during replication.

facilitate base pairing between single stranded molecules of DNA.

Answer 28

catalyze the formation of covalent bonds between adjacent nucleotides.

Question 29

Which of the following enzymes relieves the strain in DNA introduced by unwinding in E. coli?
gyrase
primase
helicase
ligase

Answer 29

gyrase