Deck 5: DNA and Chromosomes

Question 1

Mitotic chromosomes were first visualized with the use of very simple tools: a basic light microscope and some dyes.Which of the following characteristics of mitotic chromosomes reflects how they were named?

A)motion
B)color
C)shape
D)location

Answer 1

B

Question 2

What type of macromolecule helps package DNA in eukaryotic chromosomes?

A)lipids
B)carbohydrates
C)proteins
D)RNA

Answer 2

C

Question 3

Which of the following chemical groups is NOT used to construct a DNA molecule?

A)five-carbon sugar
B)phosphate
C)nitrogen-containing base
D)six-carbon sugar

Answer 3

D

Question 4

The classic "beads-on-a-string" structure is the most decondensed chromatin structure possible and is produced experimentally.Which chromatin components are NOT retained when this structure is generated?

A)linker histones
B)linker DNA
C)nucleosome core particles
D)core histones

Question 5

The relationship between the nucleic acid sequence over a stretch of DNA and the order of amino acids in the resulting protein is referred to as the __________ code.

A)protein
B)genetic
C)translational
D)expression

Question 6

The DNA from two different species can often be distinguished by a difference in the

A)ratio of A + T to G + C.
B)ratio of A + G to C + T.
C)ratio of sugar to phosphate.
D)presence of bases other than A, G, C, and T.

Question 7

Which of the following questions would NOT be answered by using karyotyping?

A)Is the individual genetically female or male?
B)Do any of the chromosomes contain pieces that belong to other chromosomes?
C)Does the individual have an extra chromosome?
D)Do any chromosomes contain point mutations?

Question 8

The chromosomes we typically see in images are isolated from mitotic cells.These mitotic chromosomes are in the most highly condensed form.Interphase cells contain chromosomes that are less densely packed and

A)occupy discrete territories in the nucleus.
B)share the same nuclear territory as their homolog.
C)are restricted to the nucleolus.
D)are completely tangled with other chromosomes.

Question 9

Which of the following structural characteristics is NOT normally observed in a DNA duplex?

A)purine-pyrimidine pairs
B)external sugar-phosphate backbone
C)uniform left-handed twist
D)antiparallel strands

Question 10

The human genome is divided into linear segments and packaged into structures called chromosomes.What is the total number of chromosomes found in each of the somatic cells in your body?

A)22
B)23
C)44
D)46

Question 11

The process of sorting human chromosome pairs by size and morphology is called karyotyping.A modern method employed for karyotyping is called chromosome painting.How are individual chromosomes "painted"?

A)with a laser
B)using fluorescent antibodies
C)using fluorescent DNA molecules
D)using green fluorescent protein

Question 12

The human genome is a diploid genome.However, when germ-line cells produce gametes, these specialized cells are haploid.What is the total number of chromosomes found in each of the gametes (egg or sperm) in your body?

A)22
B)23
C)44
D)46

Question 13

Mitotic chromosomes are __________ times more compact than a DNA molecule in its extended form.

A)10,000
B)100,000
C)1000
D)100

Question 14

The complete set of information in an organism's DNA is called its

A)genetic code.
B)coding sequence.
C)gene.
D)genome.

Question 15

DNA is an information storage molecule, whose sequences serve as a template to make

A)lipids.
B)RNA.
C)polypeptides.
D)carbohydrates.

Question 16

Specific regions of eukaryotic chromosomes contain sequence elements that are absolutely required for the proper transmission of genetic information from a mother cell to each daughter cell.Which of the following is NOT known to be one of these required elements in eukaryotes?

A)protein-coding regions
B)origins of replication
C)telomeres
D)centromeres

Question 17

In a DNA double helix,

A)the two DNA strands are identical.
B)purines pair with purines.
C)thymine pairs with cytosine.
D)the two DNA strands run antiparallel.

Question 18

Nucleosomes are formed when DNA wraps __________ times around the histone octamer in a __________ coil.

A)2.0; right-handed
B)2.5; left-handed
C)1.7; left-handed
D)1.3; right-handed

Question 19

Interphase chromosomes are about __________ times less compact than mitotic chromosomes, but still are about __________ times more compact than a DNA molecule in its extended form.

A)10; 1000
B)20; 500
C)5; 2000
D)50; 200

Question 20

Which of the following DNA strands can form a DNA duplex by pairing with itself at each position?

A)5′-AAGCCGAA-3′
B)5′-AAGCCGTT-3′
C)5′-AAGCGCAA-3′
D)5′-AAGCGCTT-3′

Question 21

Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the "histone code." Which of the following patterns will probably lead to gene silencing?

A)lysine 9 methylation
B)lysine 4 methylation and lysine 9 acetylation
C)lysine 14 acetylation
D)lysine 9 acetylation and lysine 14 acetylation

Question 22

Which of the following best describes the mechanism by which chromatin-remodeling complexes "loosen" the DNA wrapped around the core histones?

A)They use energy derived from ATP hydrolysis to change the relative position of the DNA and the core histone octamer.
B)They chemically modify the DNA, changing the affinity between the histone octamer and the DNA.
C)They remove histone H1 from the linker DNA adjacent to the core histone octamer.
D)They chemically modify core histones to alter the affinity between the histone octamer and the DNA.

Question 23

Hershey and Chase used radiolabeled macromolecules to identify the material that contains heritable information.What radioactive material was used to track DNA during this experiment?

A)³H
B)¹⁴C
C)³⁵S
D)³²P

Question 24

Most eukaryotic cells only express 20-30% of the genes they possess.The formation of heterochromatin maintains the other genes in a transcriptionally silent (unexpressed) state.Which histone modification is associated with the formation of the most common type of heterochromatin?

A)H3 lysine 4 methylation
B)H3 lysine 9 methylation
C)H3 lysine 14 methylation
D)H3 lysine 27 methylation

Question 25

Many of the breakthroughs in modern biology came after Watson and Crick published their model of DNA in 1953.However, chromosomes were identified earlier.In what decade did scientists first identify chromosomes?

A)1880s
B)1920s
C)1940s
D)1780s

Question 26

Which of the following is NOT a chemical group commonly found on core histone N-terminal tails for chromatin regulation?

A)methyl
B)sulfhydryl
C)phosphoryl
D)acetyl

Question 27

The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin.What is the result of heterochromatin formation?

A)increase in gene expression
B)gene silencing
C)recruitment of remodeling complexes
D)displacement of histone H1

Question 28

How do changes in histone modifications lead to changes in chromatin structure?

A)They directly lead to changes in the positions of the core histones.
B)They change the affinity between the histone octamer and the DNA.
C)They help recruit other proteins to the chromatin.
D)They cause the histone N-terminal tails to become hyperextended.

Question 29

Stepwise condensation of linear DNA happens in five different packing processes.Which of the following four processes has a direct requirement for histone H1?

A)formation of "beads-on-a-string"
B)formation of the 30-nm fiber
C)looping of the 30-nm fiber
D)packing of loops to form interphase chromosomes

Question 30

The core histones are small, basic proteins that have a globular domain at the C-terminus and a long, extended conformation at the N-terminus.Which of the following is NOT true of the N-terminal "tail" of these histones?

A)It is subject to covalent modifications.
B)It extends out of the nucleosome core.
C)It binds to DNA in a sequence-specific manner.
D)It helps DNA pack tightly.

Question 31

In the 1940s, proteins were thought to be the more likely molecules to house genetic information.What was the primary reason that DNA was not originally believed to be the genetic material?

A)DNA has a high density of negative charges.
B)Nucleotides were known to be a source of chemical energy for the cell.
C)Both protein and nucleic acids were found to be components of chromosomes.
D)DNA was found to contain only four different chemical building blocks.

Question 32

Fred Griffith studied two strains of Streptococcus pneumonia, one that causes a lethal infection when injected into mice, and a second that is harmless.He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection.But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse.What did Griffith conclude from this experiment?

A)The infectious strain cannot killed by heating.
B)The heat-killed pathogenic bacteria "transformed" the harmless strain into a lethal one.
C)The harmless strain somehow revived the heat-killed pathogenic bacteria.
D)The mice had lost their immunity to infection with S.pneumoniae.

Question 33

Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule.Chromatin-remodeling complexes provide this access by

A)recruiting other enzymes.
B)modifying the N-terminal tails of core histones.
C)using the energy of ATP hydrolysis to move nucleosomes.
D)denaturing the DNA by interfering with hydrogen-bonding between base pairs.

Question 34

The inactivation of one X chromosome is established by the directed spreading of heterochromatin.The silent state of this chromosome is __________ in the subsequent cell divisions.

A)completed
B)switched
C)erased
D)maintained

Question 35

Using terms from the list below, fill in the blanks in the following brief description of the experiment with Streptococcus pneumoniae that identified which biological molecule carries heritable genetic information.Some terms may be used more than once.
carbohydrate lipid R-strain
DNA nonpathogenic RNA
identify pathogenic S-strain
label purify transform
Cell-free extracts from S-strain cells of S.pneumoniae were fractionated to __________ DNA, RNA, protein, and other cell components.Each fraction was then mixed with __________ cells of S.pneumoniae.Its ability to change these into cells with __________ properties resembling the __________ cells was tested by injecting the mixture into mice.Only the fraction containing __________ was able to __________ the __________ cells to __________ (or __________) cells that could kill mice.

Question 36

You are a virologist interested in studying the evolution of viral genomes.You are studying two newly isolated viral strains and have sequenced their genomes.You find that the genome of strain 1 contains 25% A, 55% G, 20% C, and 10% T.You report that you have isolated a virus with a single-stranded DNA genome.Based on what evidence can you make this conclusion?

A)because single-stranded genomes always have a large percentage of purines
B)by using the formula G − A = C + T
C)because double-stranded genomes have equal amounts of A and T
D)because single-stranded genomes have a higher rate of mutation

Question 38

Several experiments were required to demonstrate how traits are inherited.Which scientist or team of scientists first demonstrated that cells contain some component that can be transferred to a new population of cells and permanently cause changes in the new cells?

A)Griffith
B)Watson and Crick
C)Avery, MacLeod, and McCarty
D)Hershey and Chase

Question 39

Several experiments were required to demonstrate how traits are inherited.Which scientist or team of scientists obtained definitive results demonstrating that DNA is the genetic molecule?

A)Griffith
B)Watson
C)Crick
D)Hershey and Chase

Question 40

The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner.Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle.Which of the following histone proteins does NOT form part of the octameric core?

A)H4
B)H2A
C)H3
D)H1

Question 41

The structures of the four bases in DNA are given in Figure 5-42.
Figure 5-42
A.Which are purines and which are pyrimidines?
B.Which bases pair with each other in double-stranded DNA?

Question 42

Gene A, which is normally expressed, has been moved by DNA recombination near an area of heterochromatin.None of the daughter cells produced after this recombination event express gene A, even though its DNA sequence is unchanged.Explain this observation.

Question 43

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once.
bands extended kinetochore
chromatin homologous nonhomologous
chromosomes hybridization
condensation karyotype
In eukaryotic __________, DNA is complexed with proteins to form __________.The paternal and maternal copies of human Chromosome 1 are __________, whereas the paternal copy of Chromosome 1 and the maternal copy of Chromosome 3 are __________.Cytogeneticists can determine large-scale chromosomal abnormalities by looking at a patient's __________.Fluorescent molecules can be used to paint a chromosome, by a technique that employs DNA __________, and thereby to identify each chromosome by microscopy.

Question 45

Because hydrogen bonds hold the two strands of a DNA molecule together, the strands can be separated without breaking any covalent bonds.Every unique DNA molecule "melts" at a different temperature.In this context, T_m (melting temperature) is the point at which two strands separate, or become denatured.Order the DNA sequences listed below according to relative melting temperatures (from lowest T_m to highest T_m).Assume that they all begin as stable double-stranded DNA molecules.Explain your answer.
A.GGCGCACC
B.TATTGTCT
C.GACTCCTG
D.CTAACTGG

Question 47

Origins of replication typically have a relatively high number of A-T base pairs.How does this sequence feature relate to the function of these DNA regions?

Question 48

A.Define a "gene."
B.Consider two different species of yeast that have similar genome sizes.Is it likely that they contain the same number of genes? A similar number of chromosomes?

Question 49

Explain the differences between chromosome painting and the older, more traditional method of staining chromosomes being prepared for karyotyping.Highlight the way in which each method identifies chromosomes by the unique sequences they contain.

Question 51

For each of the following sentences, choose one of the options enclosed in square brackets to make a correct statement about nucleosomes.
A.Nucleosomes are present in [prokaryotic/eukaryotic] chromosomes, but not in [prokaryotic/eukaryotic] chromosomes.
B.A nucleosome contains two molecules each of histones [H1 and H2A/H2A and H2B] as well as of histones H3 and H4.
C.A nucleosome core particle contains a core of histone with DNA wrapped around it approximately [twice/three times/four times].
D.Nucleosomes are aided in their formation by the high proportion of [acidic/basic/polar] amino acids in histone proteins.
E.Nucleosome formation compacts the DNA into approximately [one-third/one-hundredth/one-thousandth] of its original length.

Question 52

Early studies of chromosome structure relied on isolating chromatin from cells followed by nuclease treatment in vitro, followed by analysis of the products of this treatment.Demonstrate your understanding of this process by answering the questions below:
A.How can nucleosome core particles be isolated from chromatin?
B.What molecular components were identified after this treatment was complete?
C.What portion of the nucleosome was destroyed/removed during this treatment and what function does it normally serve?

Question 53

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once.
10,000 chromosome mitosis
100 different nuclear envelope
1000 DNA nucleolus
cell cycle dynamic proteins
cell wall interphase similar
chromatin lipids static
Each chromosome is a single molecule of __________ whose extraordinarily long length can be compacted by as much as __________-fold during __________ and tenfold more during __________.This is accomplished by binding to __________ that help package the DNA in an orderly manner so it can fit in the small space delimited by the __________.The structure of the DNA-protein complex, called __________, is highly __________ over time.

Question 54

In principle, what is the minimum number of nucleotides necessary to code for each amino acid? Keep in mind there are twenty different naturally-occurring amino acids, and that each amino acid is encoded by the same number of nucleotides.

Question 55

Evidence suggests that the replication of DNA packaged into heterochromatin occurs later than the replication of other chromosomal DNA.What is the simplest possible explanation for this phenomenon?

Question 56

Given the sequence of one strand of a DNA helix (below), provide the sequence of the complementary strand and label the 5′ and 3′ ends.
5′-GCATTCGTGGGTAG-3′

Question 57

The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body.Answer the quantitative questions below by choosing one of the numbers in the following list:
23 69 >200
46 92 >10⁹
A.How many centromeres are in each cell? What is the main function of the centromere?
B.How many telomeres are in each cell? What is their main function?
C.How many replication origins are in each cell? What is their main function?

Question 58

Describe the mechanism by which heterochromatin can spread, once it has been established in one region of the chromosome.

Question 60

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once.
30-nm fiber heterochromatin linker
active chromatin histone H1 loops
axis histone H3 more
beads-on-a-string histone H4 synaptic complex
euchromatin less zigzag
Interphase chromosomes contain both darkly staining __________ and more lightly staining __________.Genes that are being transcribed are thought to be packaged in a __________ condensed type of euchromatin.Nucleosome core particles are separated from each other by stretches of __________ DNA.A string of nucleosomes coils up with the help of __________ to form the more compact structure of the __________.A __________ model describes the structure of the 30-nm fiber.The 30-nm chromatin fiber is further compacted by the formation of __________ that emanate from a central __________.

Question 61

You are studying a newly identified chromatin-remodeling complex, which you call NICRC.You decide to run an in vitro experiment to characterize the activity of the purified complex.Your molecular toolbox includes: (1) a 400-base-pair DNA molecule that has a single recognition site for the restriction endonuclease EcoRI, an enzyme that cleaves internal sites on double-stranded DNA (dsDNA); (2) purified EcoRI enzyme; (3) purified DNase I, a DNA endonuclease that will cleave dsDNA at nonspecific sites if they are exposed; and (4) core octamer histones.You are able to assemble core nucleosomes on this DNA template and test for NICRC activity.Figure 5-67A illustrates the DNA template used and indicates both the location of the EcoRI cleavage site and the size of the DNA fragments that are produced when it cuts.Figure 5-67B illustrates how the DNA molecules in your experiment looked after separation according to size by using gel electrophoresis.Your experiment had a total of six samples, each of which was treated according to the legend below the gel.The sizes of the DNA fragments observed are indicated on the left side of the gel.
Figure 5-67
A.Explain the results in lanes 1-4 and why it is important to have this information before you begin to test your remodeling complex.
B.What can you conclude about your purified remodeling complex from the results in lanes 5 and 6?

Question 62

When double-stranded DNA is heated, the two strands separate into single strands in a process called melting or denaturation.The temperature at which half of the duplex DNA molecules are intact and half have melted is defined as the T_m.
A.Do you think T_m is a constant, or can it depend on other small molecules in the solution? Do you think high salt concentrations increase, decrease, or have no effect on T_m?
B.Under standard conditions, the expected melting temperature in degrees Celsius can be calculated from the equation T_m = 59.9 + [0.41 × %(G + C)] − (675/length of duplex).Does the T_m increase or decrease if there are more G + C (and thus fewer A + T) base pairs? Does the T_m increase or decrease as the length of DNA increases? Why?
C.Calculate the predicted T_m for a stretch of double helix that is 100 nucleotides long and contains 50% G + C content.

Question 63

For a better understanding of DNA structure, it helps to be able to compare physical characteristics evident from a side view of double-stranded DNA with those of individual base pairs.
A.Use brackets to designate the major and minor grooves on Figure 5-68A and shade in the surface that will be exposed in the major groove in Figure 5-68B.
B.If base pairs were aligned and stacked directly on top of each other, the major and minor grooves would be linear depressions all along the DNA.Explain why this is not the actual conformation of a DNA molecule.
Figure 5-68

Question 64

Avery, MacLeod, and McCarty carried out experiments to identify the class of biological molecule that carries heritable information.Explain how they identified the "transforming principle" that could convert a harmless strain of bacteria to a pathogenic one.

Question 65

A.Explain the reason why the cell requires a mechanism for identifying specific sequences of DNA.
B.On average, how often would the nucleotide sequence CGATTG be expected to occur in a DNA strand 4000 bases long? Show your work and explain your answer.
C.Molecular processes depend upon sequence-specific interactions of proteins with DNA.Recognition sequences can be 4, 5, 6, 7, or even 8 base pairs in length for a single protein.What might be the advantages of a short recognition sequence? What might be the advantage of a longer recognition sequence?

Question 66

Consider the structure of the DNA double helix.
A.You and a friend want to split a double-stranded DNA molecule so you each have half.Is it better to cut the length of DNA in half so each person has a shorter length, or to separate the strands and each take one strand? Explain.
B.In the original 1953 publication describing the discovery of the structure of DNA, Watson and Crick wrote, "It has not escaped our notice that the specific pairings we have postulated immediately suggest a possible copying mechanism for the genetic material." What did they mean?

Question 67

The number of cells in an average-sized adult human is on the order of 10¹⁴.Use this information, and the estimate that the length of DNA contained in each cell is 2 m, to do the following calculations (look up the necessary distances and show your working):
A.Over how many miles would the total DNA from the average human stretch?
B.How many times would the total DNA from the average human wrap around the planet Earth at the Equator?
C.How many times would the total DNA from the average human stretch from Earth to the Sun and back?
D.How many times would the total DNA from the average human stretch from the Earth to Pluto and back?

Question 68

Use the terms listed to fill in the blanks in Figure 5-69.
A.A-T base pair
B.G-C base pair
C.deoxyribose
D.phosphodiester bonds
E.purine base
F.pyrimidine base
Figure 5-69

Question 69

Using the structures in Figure 5-70 as a guide, sketch the hydrogen bonds between the base pairs in DNA.Hint: The bases in the figure are all drawn with the −NH− that attaches to the sugar at the bottom of the structure.
Figure 5-70