Deck 2: DNA and RNA: Composition and Structure

Question 1

Restriction endonucleases

A) digest DNA duplex molecules from the 5'-OH ends.
B) attack only single stranded DNA.
C) have base sequence specificity.
D) randomly digest double stranded DNA molecules.
E) are not produced by bacteria.

Answer 1

have base sequence specificity.

Question 2

Denaturation of a double stranded DNA molecule can commonly be achieved by

A) heating a DNA solution to K.
B) adding a nonionic surfactant.
C) saturating the DNA solution with NaCl.
D) all of the above.
E) none of the above.

Answer 2

none of the above.

Question 3

Which of the following would contribute to a more stable interaction between histones and DNA?

A) phosphorylation of histones
B) deacetylation of histones
C) raising the NaCl concentration
D) raising the temperature
E) methylation of the DNA

Answer 3

deacetylation of histones

Question 4

In the Watson-Crick structure for DNA

A) the DNA strands run parallel.
B) the ratio of G to A equals 1.
C) the ratio of A to U equals 1.
D) the number of purines equals the number of pyrimidines.
E) two of the above are correct.

Question 5

In the conversion of B-DNA to Z-DNA, all of the following make contributions EXCEPT

A) the presence of 5-methylcytosine.
B) a purine-rich strand base-paired to a pyrimidine-rich strand.
C) negative supercoiling.
D) alternating purines and pyrimidines on one strand.

Question 6

What are the complementary base pairs in DNA?

A) Adenine : Uracil and Guanine : Cytosine
B) Adenine : Thymine and Guanine : Uracil
C) Adenine : Guanine and Uracil : Cytosine
D) Adenine : Thymine and Guanine : Cytosine
E) Adenine : Cytosine and Guanine : Thymine

Question 7

Which is true about mRNA?

A) It contains a _OH at the 5' carbon of its ribose moieties.
B) A copy of its nucleotide sequence can be found in the genetic material
C) Analysis of its nucleotide composition reveals that it obeys Chargaff's rules.
D) It contains a hydrogen at the 2' carbon of its ribose moieties.

Question 8

The term denaturation, when used in connection with nucleic acids or proteins refers to a change in structural characteristics due to

A) the disruption of covalent bonds.
B) the disruption of non-covalent bonds.
C) the binding of toxic compounds.
D) changes in primary structure.
E) changes in the state of aggregation.

Question 9

Which one of the following nitrogenous bases has an amino group at position 2 and an oxygen at position 6?

A) Adenine
B) Guanine
C) Uracil
D) Thymine
E) Hypoxanthine

Question 10

Which of these statements is not true regarding the three classes of RNA, ribosomal RNA, mRNA and tRNA?

A) All three classes are involved in protein synthesis.
B) Ribosomal RNA is cleaved from a large precursor RNA species.
C) tRNA and ribosomal RNA contain methylated bases.
D) A single amino acyl tRNA synthetase can attach different amino acids to -C-C-A-OH end of tRNA molecules.

Question 11

Which of the following statements is not true about the human genome?

A) It is present in each somatic (i.e., not germline) cell in diploid form.
B) It contains a mixture of repetitive and unique sequence DNA.
C) The DNA in each chromosome consists of a circle.
D) It encodes information for the targeting of proteins to their proper cellular locations.
E) It contains approximately 2.4 x 19 bp (haploid content).

Question 12

Which type of nucleic acid forms a high energy bond with an amino acid during protein synthesis?

A) Messenger RNA
B) Mitochondrial DNA
C) Nuclear DNA
D) Ribosomal RNA
E) Transfer RNA

Question 13

Each of the following describes tRNA EXCEPT

A) the end terminates in CCA.
B) it is synthesized with extra bases on the and 5' ends.
C) its extended structure looks like a cloverleaf.
D) it furnishes a codon for protein synthesis.
E) it has many bases which are modified.

Question 14

Which of the following statements about supercoiling of DNA are true?
(1) Supercoiled DNA differs in linking number from relaxed DNA.
(2) Supercoiled DNA can be relaxed through the action of topoisomerases.
(3) All DNA in the cell is positively supercoiled.
(4) A negatively supercoiled DNA is more difficult to unwind.

A) Only 2, 3 and 4 are true
B) Only 1, 2 and 3 are true
C) Only 1 and 3 are true
D) Only 1 and 2 are true
E) All are true

Question 15

Which of the following is a general feature of both DNA and RNA?

A) In vivo they are double helical structures formed from two separate chains.
B) They are alkaline stable.
C) They form complementary G-C base pairs.
D) They contain small amounts of pseudouridine.
E) They interact with histones to form nucleosomes.

Question 16

The Tm (melting temperature) of DNA

A) is unrelated to the base composition.
B) is a constant for all DNA samples.
C) is linearly related to the guanine + cytosine content.
D) is proportional to the uridine content.
E) None of the other answers is correct.

Question 17

Which of the following statements about supercoiling of DNA are true? (1) Supercoiled DNA differs in linking number from relaxed DNA.
(2) Supercoiled DNA can be relaxed through the action of topoisomerases.
(3) All DNA in the cell is positively supercoiled.
(4) A negatively supercoiled DNA is more difficult to unwind.

A) Only 2, and 4 are true
B) Only 1, 2 and re true
C) Only 1 and re true
D) Only 1 and 2 are true
E) All are true

Question 18

The conversion of B_DNA to Z_DNA is facilitated by

A) sequences rich in A-T base pairs.
B) increasing NaCl concentration.
C) negative supercoiling.
D) histone acetylation.

Question 19

All of the following statements concerning histones are true EXCEPT that they

A) are rich in arginine and lysine.
B) are proteins of relatively low molecular weight.
C) exhibit known interspecies homologies in their amino acid sequences.
D) are noncovalently attached to DNA in stoichiometric amounts.
E) exhibit a wide variety of non-homologous molecular structure.

Question 20

The Watson-Crick model of the DNA double-helix led to the prediction that DNA replication is semi-conservative because

A) the phosphate backbones could be easily broken and rejoined.
B) the double-helix can assume either B-form or Z-form higher order structure before DNA replication.
C) each strand could serve as a template for daughter strand synthesis producing pairs of identical molecules.
D) the hydrogen bonds would stabilize important intermediates that arise during synthesis.
E) it would position the reactive OH favorably for formation of the phosphodiester bond.

Question 21

Which of the following statements is incorrect concerning the function of chromatin:

A) chromatin condenses the DNA
B) chromatin plays a role in the regulation of gene expression
C) chromatin allows for the tight packaging of DNA into sperm heads
D) chromatin compacts DNA in a manner that allows regulatory sequences to be exposed
E) none of the above

Question 22

The major structural protein component(s) of chromatin are

A) tubulin.
B) actin.
C) histones.
D) acidic chromosomal proteins.
E) myosin.

Question 23

The nucleosome is the basic repeating unit of chromatin. Which of the following statements concerning nucleosomes is incorrect:

A) nucleosomes have protein cores consisting of an octamer of protein subunits
B) a segment of DNA approximately 145 bp long is associated with each nucleosome
C) histone H1 contacts the DNA linker segments as they enter and leave the nucleosome
D) the DNA in a nucleosome is packed tightly inside the protein core to conserve space in the nucleus and to protect the DNA from damage
E) some nucleosomes form over specific regions of DNA in a non_random manner

Question 24

All of the following statements concerning properties of nucleic acids are correct EXCEPT

A) RNA is hydrolyzed to 2'- and nucleotides by alkali.
B) DNA is denatured by alkali.
C) DNA is denatured by high temperature.
D) Denaturation of DNA is accompanied by hyperchromism.
E) RNA cannot form a Watson-Crick type double-helix.

Question 25

Which of the following statements is correct concerning native DNA?

A) The two strands are the same in base sequence.
B) The sugar-phosphate backbones contain the five carbon sugar ribulose.
C) The analysis A = G and C = T is expected.
D) The structure can be disrupted by high salt.
E) None of the above.

Question 26

Heterogeneous nuclear RNA (hnRNA) can contain all the following EXCEPT

A) sequences which can base pair with small nuclear RNA (snRNA).
B) sequences derived from the TATA region of the promoter.
C) introns.
D) polyadenylate.
E) codons.

Question 27

A segment of DNA has the following sequence pTpApCpGpTpGpC-H. Which of the sequences below would represent the complement of this DNA strand? (Note, all sugars are deoxyribose)

A) pApTpGpCpApCpG-H
B) pGpCpTpGpCpApTp-H
C) pGpCpApCpGpTpA-H
D) pTpApCpGpTpGpC-H
E) none of the above

Question 28

Which of the following are found in the 60S ribosomal subunit?

A) 5S rRNA
B) l8S rRNA
C) 28S rRNA
D) Both A and B
E) Both A and C

Question 29

Denaturation of double_stranded DNA with heat or alkali results in all of the following EXCEPT

A) decreased absorbance of the DNA at 260 nm.
B) loss of base stacking.
C) formation of single_stranded DNA.
D) disruption of hydrogen bonding.
E) a helix_to_coil transition.

Question 30

Restriction enzymes are:

A) DNA polymerases
B) RNA polymerases
C) endonucleases
D) exonucleases
E) none of the above

Question 31

By which of the following means are the nucleosides linked to one another in RNA and DNA molecules?

A) They are linked together by alpha-glycosidic bonds.
B) They are linked together by beta-glycosidic bonds.
C) They are linked together by 5' phosphodiester bridges.
D) They are linked together by 2',5' phosphodiester bridges.
E) None of the other answers is correct.

Question 32

What is the main difference between topoisomerases I and II?

A) Gyrases are a subset of topoisomerases I
B) Topoisomerase I breaks one strand and II both strands
C) Topoisomerase I needs ATP, and II does not
D) Topoisomerase II remains bound to DNA until religation
E) Topoisomerase relaxes only positively supercoiled species

Question 33

One of the following five statements describing the Watson-Crick model for double stranded DNA is incorrect. INDICATE THE INCORRECT STATEMENT

A) The two strands of DNA are intertwined in such a way that they can be separated without unwinding the complementary strand.
B) The paired chains have opposite polarity.
C) The paired bases are located in the interior of the double helical structure.
D) One turn of the double helix involves approximately 10 nucleotides and occurs every angstroms.
E) The double helical structure has two grooves running helically along its length, one of which is considerably narrower than the other.

Question 34

The stem-loop structure of tRNA is associated with which of the following important functional regions?

A) the anti-codon site
B) the amino acid attachment site
C) the 5' cap site
D) the polyadenylation site
E) the intron

Question 35

Which of the following is a ribonucleoside which contains an amino group?

A) Thymine
B) Uridine
C) Thymidine
D) Cytidine
E) Deoxyadenosine

Question 36

Histones:

A) account for 1/4 the mass of the eukaryotic chromosome.
B) complex with RNA to form spliceosomes.
C) are bound to DNA in the transcriptional units of both active and inactive genes.
D) are small Glu+Asp_ rich proteins that facilitate compaction of eukaryotic DNA in the nucleus.
E) are a highly conserved class of proteins with the most conserved being the linker histone Hl.

Question 37

Chemicals that bind to DNA by intercalating between the bases

A) can cause frame shift mutations.
B) can cause deletion mutations.
C) can cause insertion mutations.
D) are generally planar hydrophobic molecules.
E) all of the above

Question 38

The type of nucleic acid that may contain small quantities of a variety of modified ribonucleotides is

A) messenger RNA.
B) ribosomal RNA.
C) nucleolar RNA.
D) transfer RNA.
E) mitochondrial RNA.

Question 39

Each of the following statements concerning DNA structure is true EXCEPT which one?

A) [A] + [T] = [G] + [C] in normal double stranded DNA.
B) [A] + [G] = [T] + [C] in normal double stranded DNA.
C) [Purines] = [pyrimidines] in normal double stranded DNA.
D) the specificity of base pairing is due to the arrangement of H-bonds found between bases and the dimensions of the base pairs.
E) the 5 position on thymine bears a methyl group.

Question 40

The melting temperature of DNA (Tm) can be used to determine the

A) average length of the DNA.
B) complexity of the DNA.
C) percentages of A, T, G, and C in the DNA.
D) number of base pairs in the DNA.

Question 41

What is contained within a nucleoside?

A) a ribose moiety, a nitrogenous base and a phosphate covalently attached to the ribose 5' carbon
B) a ribose moiety, a purine or pyrimidine, and a phosphate covalently linked to the 3' carbon of the ribose.
C) a ribose moiety and a nitrogenous base
D) a deoxyribose, a purine or pyrimidine, and a phosphate linked to the ribose 5' carbon by a hydrogen bond.

Question 42

The nucleotide sequence 5'-ATTGCAG-3' should base pair with

A) 5'-TAACGTC-3'.
B) 5'-CTGCAAT-3'.
C) 3'-ATTGCAG-5'.
D) 3'-CTGCAAT-5'.

Question 43

Restriction enzymes have all of the following characteristics EXCEPT that they cut

A) DNA sequence specifically.
B) each DNA strand separately.
C) palindromic sequences.
D) DNA using an exonuclease activity.

Question 44

Enzymes that catalyze stepwise hydrolysis of mononucleotides from one end of a polynucleotide chain are

A) polymerases.
B) endonucleases.
C) ligases.
D) exonucleases.
E) nickases.

Question 45

In the double helical structure of DNA, adenine is hydrogen bonded to

A) uridine.
B) cytosine.
C) guanine.
D) thymine.

Question 46

The H1 histone

A) is one of the four histones in the nucleosome core.
B) helps form the octamer nucleosome complex.
C) is one of the two arginine-rich histones.
D) is present at 1:1 weight ratio with DNA.
E) helps fold the bead-on-a-string structure into higher order structures.

Question 47

Which best describes the mechanism of OH--mediated denaturation of DNA?

A) OH- disrupts the H-bonding between the nitrogenous bases of opposing DNA strands.
B) OH- hydrolyzes the phosphodiester linkages between nucleotides.
C) The hydroxyl ions attract the unpaired electrons of the amino groups attached to the nitrogenous bases.
D) Alkali tends to increase the melting temperature of DNA.

Question 48

Which of the following determines the specificity of nucleic acid hybridization?

A) base composition
B) A-T and G-C hydrogen bonds
C) sequence complexity
D) stacking interactions
E) wobble rules

Question 49

Each of the following statements concerning the complementary strands of DNA is true EXCEPT which one?

A) The pyrimidine content of each strand is the same.
B) The sum of the G and C content in one strand equals the sum of the G and C content in the other strand.
C) The percent purines in one strand must equal the percent pyrimidines in the other strand.
D) If one strand contains the sequence pGpApApTpTpC, the other strand must contain the same sequence.
E) If one strand contains thymine, the other strand must contain adenine.

Question 50

Which one of the following terms best describes the complete structure of a nitrogenous base with oxygens at positions 2 and 4 and ribose at position 1?

A) Thymine
B) Uracil
C) Thymine ribonucleoside
D) Uridine
E) Cytidine

Question 51

All of the following statements regarding the Watson-Crick B form of DNA are true EXCEPT

A) two chains are coiled around a common axis forming a right-handed helix.
B) there are 10 base pairs per turn.
C) the bases are found on the outside of the helix and the sugar phosphate backbone on the inside.
D) the two chains run in opposite directions.
E) adenine is always paired with thymine, guanine with cytosine.

Question 52

What is the PRINCIPAL force holding the two strands of the double helix together?

A) base pairing
B) covalent bonding
C) hydrophobic interactions
D) stacking forces

Question 53

Hyperchromic shift is caused by

A) high GC content.
B) high AT content.
C) melting of double stranded DNA.
D) cooling of double stranded DNA.
E) none of the above

Question 54

Restriction endonucleases are enzymes that

A) synthesize DNA from a RNA primer.
B) nick single strands of DNA.
C) cleave both strands of DNA at sequence specific sites.
D) add nucleotides to the end of DNA strands.
E) None of the other answers is correct.

Question 55

Histones are

A) basic proteins associated with RNA.
B) basic proteins associated with DNA.
C) acidic proteins which bind chromosomal nucleoprotein.
D) proteins exclusively found in the nucleolus.
E) proteins which are tissue specific.

Question 56

What is the nature of the usual linkage between nucleic acids and proteins in nucleoproteins?

A) Hydrogen bonding.
B) Covalent ester formation between phosphoric acid of nucleic acids and basic amino acids of proteins.
C) Ionic linkages between phosphoric acid of nucleic acids and basic amino acids of proteins.
D) Van der Waals interactions between bases of nucleic acids and side chains of amino acids of protein.
E) A mixture of covalent linkages and hydrogen bonding.

Question 57

In mammalian cells, rRNA

A) accounts for of the total cellular RNA content.
B) is rapidly degraded during protein synthesis.
C) is composed of only two types - 2and 16S.
D) contains the codons for protein synthesis.
E) is composed of at least 4 different size classes of RNA.

Question 58

Each of the following statements is true EXCEPT which one?

A) DNA and RNA are both polynucleotides held together by 5' phosphodiester bonds.
B) Three of the bases are the same in both DNA and RNA.
C) Both DNA and RNA usually exist as a Watson-Crick double helix.
D) RNA is found both in the nucleus and the cytoplasm.
E) RNA but not DNA is hydrolyzed by base.

Question 59

All of the following statements concerning the Watson-Crick Model of DNA structure are true EXCEPT

A) the two strands of DNA are complementary.
B) the hydrogen bonding between guanine and cytosine is stronger than between adenine and thymine.
C) the two DNA strands are anti-parallel.
D) the nm periodicity is the distance for one complete turn of the helix.
E) the stacked nitrogenous bases form the backbone of each DNA strand.

Question 60

If in one strand of DNA, reading in the ' to direction, the nucleotide sequence is GCC, the nucleotide sequence in the complementary strand, again in the ' to direction, is

A) GCC.
B) GGC.
C) CGG.
D) ATT.
E) AAT.

Question 61

What is the difference between ribozymes that are considered "true" catalysts and those that are not?

A) "Non-true" catalysts are found only in prokaryotes
B) "Non-true" catalysts do not employ any of the accepted mechanisms of rate enhancement
C) "Non-true" catalysts do not recognize a specific site on the substrate
D) "True" catalysts are the same at the end of the reaction as at the beginning
E) "True" catalysts require a protein component

Question 62

Spontaneous conversion of adenine and cytosine from the amino to the imino forms of these bases within DNA results in

A) cleavage of the glycosidic bond and loss of the base.
B) cleavage of the 3', 5' phosphodiester DNA backbone.
C) alteration of the hydrogen bonding of the bases.
D) formation of guanine and thymine.

Question 63

All of the following statements are true concerning DNA synthesis EXCEPT

A) A major portion of the stability of double helical DNA is due to the hydrophobicity of the bases.
B) The 2' position of a nucleoside of DNA bears a phosphate group.
C) The 5' position of a nucleotide of DNA bears a phosphate group.
D) DNA absorbs UV radiation at 260 nm due to its base content.
E) Anti-parallel in DNA structure results in one strand of DNA having its 5' end opposite the end of the second strand of the double helix.

Question 64

DNA sequencing by the Sanger technique makes use of dideoxynucleotides for which of the following reasons?

A) To ensure that DNA is synthesized from only one of the two DNA strands
B) To terminate DNA synthesis at every nucleotide
C) To promote base-pairing between the newly synthesized strand and the template strand
D) To provide sites at which DNA cleavage will occur

Question 65

All of the following are TRUE regarding restriction endonucleases EXCEPT

A) they recognize specific palindromic sequences.
B) they may produce staggered ends when they cleave DNA into fragments.
C) they may produce flush ends when they cleave DNA into fragments.
D) they are used in gene cloning to cleave the single stranded regions of the cDNA produced by reverse transcriptase.
E) they are used to cleave plasmid DNA in specific places in gene cloning experiments.

Question 66

Which of the following classes of RNA contain the largest relative percentage of unusual modified purine and pyrimidine bases?

A) hnRNA
B) mRNA
C) tRNA
D) rRNA
E) All contain comparable relative percentages of modified bases.

Question 67

Which of the following observations is part of the evidence supporting the Watson-Crick structure of DNA?

A) In the DNAs examined from a wide variety of sources, the adenine and cytosine contents are equal.
B) A non-virulent pneumococcus can be transformed to a virulent strain by the addition of DNA.
C) RNA is susceptible to hydrolysis by alkali, whereas DNA is not.
D) The sum of the purines present in any double-stranded DNA is equal to the sum of the pyrimidines present.

Question 68

Histones are

A) found primarily in prokaryotic cells and not in mammalian cells.
B) believed to bind with rRNA in the formation of ribosomes.
C) acidic proteins containing a high proportion of glutamic and aspartic acid.
D) basic proteins containing a high proportion of lysine and arginine.
E) proteins that control the rate of translation of mRNA into a protein molecule.

Question 69

Which one of the following best describes the products from the base hydrolysis of RNA?

A) 2' and 3' nucleoside monophosphates
B) 5'-nucleoside monophosphates
C) Purine bases, pyrimidine nucleosides, ribose and phosphate
D) Pyrimidine bases, purine nucleosides, ribose and phosphate
E) 3' and 5' nucleoside monophosphates

Question 70

Which is not true of the structure of DNA

A) The B form of DNA is anti_parallel
B) The Z form of DNA is parallel
C) Stacking forces stabilize the Z form of DNA
D) DNA RNA hybrids are in the A form
E) Hydrophobic interactions provide the negative free energy in base pairing

Question 71

Which of the following is MOST responsible for determining the structural stability of double-stranded DNA?

A) The attractive interaction between positively charged purines and negatively charged pyrimidines.
B) H-bonding between the OH of deoxyribose and purine and pyrimidine ring nitrogens.
C) Hydrophobic interaction between contiguous base pairs and hydrogen bonding between complementary bases on opposite strands.
D) Interaction between the phosphate groups in separate chains.
E) Hydrophilic interaction between the pentoses in separate chains.

Question 72

Histones are

A) basic proteins associated with RNA.
B) basic proteins associated with DNA.
C) acidic proteins which bind chromosomal nucleoprotein.
D) proteins exclusively found in the nucleolus.
E) proteins which are tissue specific.

Question 73

Which one of the following statements is true? In chromatin folding, the structure called a solenoid

A) is the most compact form of DNA.
B) requires the presence of histone H1.
C) is a good template for transcription.
D) consists of eight histone molecules around which DNA is wrapped.
E) is the most extended form of DNA.

Question 74

All of the following statements regarding ribosomes are CORRECT EXCEPT

A) prokaryotic ribosomes are LESS complex than eukaryotic ribosomes.
B) the prokaryotic small ribosomal subunit contains a single rRNA molecule.
C) prokaryotic ribosomes resemble mitochondrial ribosomes.
D) prokaryotic and eukaryotic LARGE ribosomal subunits each contain different rRNA species.
E) prokaryotic small ribosomal subunits contain a nucleotide sequence in rRNA which is complementary to a sequence in mRNA.

Question 75

Which of the following statements uniquely applies to eukaryotic mRNA when compared to eukaryotic rRNA and tRNA?

A) It is synthesized in the nucleus.
B) It is modified after its transcription.
C) It contains methylated bases.
D) It usually contains a polyadenylic acid sequence at its terminus.
E) It is always larger than any other RNA species.

Question 76

Restriction endonucleases

A) cleave single stranded DNA preferentially.
B) cleave DNA at specific sequences only when those sequences are unmethylated.
C) remove bases one at a time from the 5' end of the DNA only when the bases are incorrectly matched with the template strand.
D) initiate the repair process by making a single endonucleolytic incision at the 5' end of the damaged DNA region.
E) are required for the correct processing of tRNA in the cell.

Question 77

Which of the following is a nucleoside found exclusively in tRNA?

A) pseudouridine
B) uridine
C) thymine
D) ribose
E) adenosine

Question 78

Which one of the following statements is true? In chromatin folding, the structure called a solenoid:

A) is the most compact form of DNA.
B) requires the presence of histone H1.
C) is a good template for transcription.
D) consists of eight histone molecules around which DNA is wrapped.
E) is the most extended form of DNA.

Question 79

Which one of the following classes of histones is not a component of the core particle?

A) H1
B) H2A
C) H2B
D) H. H4

Question 80

The histones are

A) ribosomal proteins which regulate the function of ribosomes.
B) proteins which bind to tRNAs and activate them.
C) small basic proteins associated with the DNA molecules in the chromatin of eukaryotic cells.
D) small acidic proteins which may be involved in gene regulation.
E) proteins required for binding of the mRNA to the ribosome.