Deck 5: Dna Structure, Replication, and Recombination

Question 1

The first level of compaction of DNA consists of

A) DNA winding around histones to form small nucleosomes.
B) tight coiling of DNA with nucleosomes into higher order structures.
C) high level compaction into metaphase-type chromosomes.
D) histone,DNA,and nonhistone covalent bonding.
E) DNA double helix unwinding.

Answer 1

A

Question 2

The total compaction of DNA as seen in metaphase chromosomes is approximately ______ fold.

A) 10,000
B) 50,000
C) 100,000
D) 40
E) 4

Answer 2

A

Question 3

Histones appear to have a singular role in the packaging of DNA.The nonhistone proteins in chromatin have all of the following functions except

A) compacting DNA
B) activity at different moments in the cell cycle
C) centromere function activity
D) forming the nucleosome core
E) regulating gene expression

Answer 3

D

Question 4

With regard to the typical human cell,which of the following appears to be true?

A) There is only one origin of replication.
B) There are multiple origins of replication that function consecutively.
C) There are multiple origins of replication that function simultaneously.
D) Replication is not understood well enough to postulate on replication origins.
E) The number of origins varies with the level of gene expression.

Question 5

The enzyme that some organisms use to replicate DNA at the 5' ends of chromosomes is called

A) DNA polymerase.
B) telomerase.
C) DNA ligase.
D) replicase.
E) lactamase

Question 6

The 10,000 origins of replication in mammalian cells suggests that concerning origin of replication there is

A) at least one per loop of DNA.
B) probably one every other loop of DNA.
C) a random distribution across the genome.
D) a precise pattern of distribution relative to other replication points.
E) approximately one per chromosome

Question 7

In mammalian cells,replication proceeds

A) unidirectionally.
B) bidirectionally.
C) unidirectionally from many origins.
D) bidirectionally from only one origin.
E) polydirectionally.

Question 8

At what stage of mitosis do we first see a chromosome that is compacted 250-fold over the 40-fold compacted 300Å fibre?

A) prophase
B) metaphase
C) anaphase
D) telophase
E) never achieves this level of compaction

Question 9

Yeast research with autonomously replicating sequences (ARSs),along with digestion of chromatin with DNase I,have led scientists to determine that

A) DNA is not protected inside a nucleosome.
B) ARSs are really plasmids.
C) RSs bond irreversibly to replication enzymes.
D) origins of replication are accessible regions of DNA devoid of nucleosomes.
E) ARSs replicate without DNA polymerase.

Question 10

By weight,chromatin consists roughly of

A) 1/3 DNA,1/3 histones,and 1/3 nonhistones.
B) 1/3 DNA and 2/3 acidic proteins.
C) 1/3 DNA,1/3 histones,and 1/3 basic proteins.
D) DNA,RNA,histones,and 1/4 nonhistones.
E) ¼ DNA and ¾ histones.

Question 11

The process of _________ is extremely important in generating genetic diversity.

A) translation
B) transcription
C) recombination
D) transformation
E) None of the choices are correct.

Question 12

Histones and DNA have a strong attraction for each other because

A) DNA is positively charged and histones are negatively charged.
B) both DNA and proteins are hydrophobic.
C) DNA is negatively charged and histones are positively charged.
D) like substances share common charges.
E) None of the choices are correct.

Question 13

Which of the following is not a piece of evidence that supports the radial loop-scaffold model of DNA packaging?

A) Histone-depleted metaphase chromosomes still maintain their X-like shapes.
B) Electron micrographs of whole-mounted mitotic chromosomes show loops of chromatin at the periphery of the chromosomes.
C) Topoisomerase II assists in 100Å packaging.
D) Special,irregularly spaced repetitive base sequences associate with nonhistone proteins to define the chromatin loops.
E) All of the choices are such evidence.

Question 14

The components of a chromosome include one long DNA molecule and

A) phospholipids.
B) proteins.
C) carbohydrates.
D) steroids.
E) RNA.

Question 15

An electron micrograph of chromatin,which looks like a bead on a string,allows measurement of structural dimensions.The beads appear to have a diameter of about ________ Å and the string has a diameter of about ________ Å.

A) 20;100
B) 20;0.1
C) 100;20
D) 120;100
E) 0.1;10

Question 16

Nucleosomal chromatin,with a diameter of 100Å,supercoils into a 300Å superhelix.The histone that appears to be responsible for this compaction is

A) H4.
B) H3.
C) H2.
D) H1.
E) H0.

Question 17

Which of the following is not usually seen when a cell loses telomerase activity?

A) Telomeres shorten slightly with each cell division.
B) After 30-50 divisions,cells show signs of senescence and then die.
C) Chromosomes gradually become shorter.
D) Many normal somatic cells gain the ability to divide indefinitely.
E) None of these.

Question 18

The chromosome can be considered a dynamic organelle for _______________ of DNA.

A) expression
B) segregation
C) replication
D) packaging
E) All of the choices are correct.

Question 19

Without __________ regions on the DNA during recombination,gene conversion could not occur.

A) homoduplex
B) heteroduplex
C) homotriplex
D) heterotriplex
E) None of the choices are correct.

Question 20

In DNA,the 300Å fibre is formed into structural loops.Responsibility for this function appears to lie with

A) histone H4.
B) nucleosomase.
C) histone H1.
D) certain nonhistone proteins.
E) histone H3.

Question 21

During mitosis,kinetochores develop during

A) telophase.
B) anaphase.
C) metaphase.
D) prophase.
E) cytokinesis.

Question 22

Which of the following statements about Holliday junctions is false?

A) Resolution of a Holliday junction may produce a heteroduplex and a crossover.
B) Resolution of a Holliday junction may produce a heteroduplex without a crossover.
C) There are two Holliday junctions involved in meiotic recombination.
D) Resolution of a Holliday junction may produce a crossover without a heteroduplex.
E) Resolution of a Holliday junction involves cutting one strand of two different DNA double helices.

Question 23

The two chromatids of each replicated chromosome must separate from one another and segregate during

A) mitosis.
B) meiosis I.
C) meiosis II.
D) both mitosis and meiosis I.
E) both mitosis and meiosis II.

Question 24

Which of these would compensate for a lack of telomerase?

A) A DNA polymerase that worked 5' to 3'.
B) Increased expression of primase.
C) A DNA polymerase that did not require a primer.
D) A decrease in primase activity.
E) Increased expression of histones.

Question 25

Which is of the following statements about the double strand break-repair model is true?

A) Heteroduplexes form only in chromosomes that undergo crossover.
B) Recombination is initiated by double strand breaks on each of two sister chromatids.
C) The position of the double strand break is always random.
D) Recombination occurs between non-homologous chromosomes.
E) The length of the chromatids is unchanged after recombination.

Question 26

In DNA,most satellite sequences are found in

A) chromosome arms.
B) telomeres.
C) centromeres.
D) spaces around the dark bands.
E) None of the choices are correct.

Question 27

Recombination occurs during meiotic ________.

A) anaphase
B) interphase
C) prophase
D) metaphase
E) None of the choices are correct.

Question 28

In which of the following cases will a Barr body be seen?

A) only XX
B) XY
C) XO
D) only XXY
E) both XX and XXY

Question 29

Which of the following is not true about DNA polymerase?

A) It cannot begin the 5' end of a new strand without a primer.
B) It can only travel in the 5' to 3' direction.
C) It can reconstruct the 3' end of each newly made DNA strand.
D) It can replace RNA primer with DNA at the 5' end.
E) It is an enzyme.

Question 30

During development,an XX female embryo will form one of the X chromosomes in each cell into a Barr body.This usually occurs

A) about two weeks after zygote formation.
B) by the end of the first trimester.
C) at the 16-cell stage.
D) in the X that is the most recessive.
E) in the X that is the least recessive.

Question 31

Any deviation from the expected 2:2 segregation of parental alleles that results from recombination is known as

A) allelic exchange.
B) gene conversion.
C) crossing over.
D) recombination.
E) DNA replication.

Question 32

The nicking of DNA that initiates recombination during mitosis may be due to all but

A) instruction from normal cell-cycle program.
B) X-rays.
C) chemical damage.
D) physical damage.
E) radiation.

Question 33

Which of the following are properties of telomeres?

A) Consist of special repetitive DNA sequences.
B) Prevent the loss of DNA through incomplete replication.
C) Cap the ends of each chromosome.
D) Number of repeats varies with cell type.
E) All of the choices are correct.

Question 34

Cohesins are a multisubunit protein complex that functions to

A) hold sister chromatids together.
B) ensure that proper chromosome arm length is maintained.
C) allow easy karyotyping.
D) develop meiotic chromosome replication.
E) All of the choices are correct.

Question 35

Recombination involves the breakage and reunion of DNA molecules from

A) homologous nonsister chromatids.
B) homologous sister chromatids.
C) heterologous nonsister chromatids.
D) heterologous sister chromatids.
E) None of the choices are correct.

Question 36

Which of the following statements about a heteroduplex is not true?

A) Heteroduplex formation can be initiated by a double-strand break.
B) A heteroduplex can contain mispaired C-T basepairs.
C) The length of a heteroduplex is increased by branch migration.
D) A heteroduplex can contain mispaired G-T basepairs.
E) Heteroduplexes always results in crossovers.

Question 37

In higher eukaryotes,kinetochores attach to

A) one spindle fibre.
B) one spindle fibre on each side.
C) multiple spindle fibres.
D) multiple repeating structural subunits.
E) telomeres.

Question 38

Which of these is required for first strand invasion in the double-strand break repair model?

A) blunt end double strand break on two sister chromatids
B) 3' single strand tails on one sister chromatid
C) 3' single strand tails on both sister chromatids
D) 5' single strand tails on one sister chromatid
E) 5' single strand tails on both sister chromatids

Question 39

In yeast chromosomes,centromeres

A) help distinguish one chromosome from another.
B) are closely related in sequence.
C) are only 10-15 bp long.
D) are largely euchromatic.
E) are encoded by a single,repeated nucleotide.

Question 40

One of the functions of a centromere is to contribute to proper chromosome segregation.The other function is to

A) hold sister chromatids together.
B) ensure that proper chromosome arm length is maintained.
C) allow easy karyotyping.
D) develop meiotic chromosome replication.
E) All of the choices are correct.

Question 41

Discuss how a nucleosome is constructed from DNA and histone proteins.

Question 42

Histones are small proteins composed of a preponderance of basic negatively charged amino acids.

Question 43

You examine cells with a microscope and detect that there are two Barr bodies present in each cell.What is the most likely genotype of the cells?

Question 44

Ignoring the detailed description of how DNA polymerase functions,discuss the roles that proteins play in reproducing chromatin structure.

Question 45

Describe the ways in which telomeres are critical to chromosome function.

Question 46

It appears that all origins of replication are active during all mitotic divisions that create an organism.

Question 47

Chromosomes are composed of chromatin.

Question 48

Telomerase is an enzyme that consists of a protein portion in association with RNA.

Question 49

While duplicating an entire chromosome,DNA polymerase cannot begin the 5' end of a new strand without a primer.

Question 50

The Holliday model of recombination has been modified.The current model,termed the consensus model,is now consistent with current research.What are the five properties of recombination,as they are now understood?

Question 51

Which of the following enzymes is not required for recombination in the double-strand break repair model?

A) single-stranded DN binding protein
B) DNA polymerase
C) double strand recombinase
D) ligase
E) endonuclease

Question 52

Describe the process of nucleosome decompaction that allows the transcription of RNA.

Question 53

Nucleosomes are evenly spaced along a chromosome,but they do not have a well-defined arrangement within the chromatin.

Question 54

If removal of a DNA sequence disrupts chromosome segregation and reinsertion of the same sequence restores stable transmission,the sequence must lie within the centromere.

Question 55

The linear chromosomes of eukaryotic cells terminate at both ends in protective caps called telomeres.

Question 56

Design an experiment to demonstrate that recombination involved breakage and rejoining of DNA molecules.E.coli with phage grown in either heavy or light isotopes,and then after allowing for recombination (but not replication),separated the DNA by centrifugation in a CsCl density gradient.The recombinant molecules,consisting of various combinations of heavy or light molecules,would migrate to positions in between the non-recombinant molecules,which consisted entirely of either heavy or light DNA.

Question 57

Scaffold-associated regions (SARs)likely serve to attach chromatin loops to the condensation scaffold.

Question 58

Cohesins are a multisubunit protein complex that glue sister chromatids together after chromosome replication in the S phase of the cell cycle.

Question 59

During metaphase of mitosis the chromosomes look like a tangled mass of grainy string scattered throughout the nucleus.

Question 60

That histones have changed so little throughout evolution underscores the importance of their contribution to chromatin structure.

Question 61

What observation supports the hypothesis that recombination occurs after replication? How would outcome differ if recombination preceded replication?