2018 DNA MCQ QP+MS

2018 DNA Structure and Replication MCQ2018 / H2 / AJC PRELIM / P1 Q71A simplified representation of a replication bubble is shown in the figure below. Parental strands 1 and 2 and the growing daughter strands X and Y are indicated. Which of the following statements about the synthesis of daughter strands X and Y is correct?ADaughter strands X and Y are synthesised away from their respective replication forks.BDaughter strand X is synthesised continuously while daughter strand Y is synthesised in the form of Okazaki fragments.CDaughter strand X is synthesised in the 5’ → 3’ direction while daughter strand Y is synthesised in the 3’ → 5’ direction.DTo synthesise daughter strands X and Y, both parental strands 1 and 2 are read in the 3’ to 5’ direction. 2018 / H2 / ACJC PRELIM / P1 Q82In an investigation to study the mode of DNA replication, Escherichia coli (E. coli) cells were grown in a nutrient medium containing heavy isotope of nitrogen (15N) for an extended period of time until all the DNA was labelled. These E. coli cells were then transferred to a nutrient medium containing only light isotope of nitrogen (14N) and were allowed to multiply over three generations. The DNA of the E. coli cells was then harvested at nine different time intervals. Subsequently, density gradient centrifugation of these E. coli DNA using caesium chloride was performed.

The diagram shows the results obtained. Which statements are consistent with the results observed?1The generation time for E.coli is about 20 minutes. 2In the 1st generation, only hybrid 14N/15N DNA was produced.3In the 3rd generation, 75% hybrid 14N/15N DNA and 25% light 14N/14N DNA were produced.4In the subsequent 4th generation, only light 14N/14N DNA would be produced.A1 and 2B2 and 3C1 and 4D1, 3 and 4

2018 / H2 / DHS PRELIM / P1 Q133The figure below shows a DNA molecule. Which statement(s) correctly describe the polynucleotide?1The structure labelled A corresponds to that of a purine, while the structure labelled B corresponds to that of a pyrimidine. 2The antiparallel nature of DNA double helix allows phosphodiester bonds to form between the nitrogenous bases of opposite strands.3Width of DNA double helix is 2µm.4The wound DNA double helix consists of alternating major grooves and minor grooves along its axis.A1 onlyB1 and 4 onlyC2 and 3 onlyD1, 3 and 4 only

2018 / H2 / DHS PRELIM / P1 Q154DNA replication is illustrated in the following figure. Which of the following correctly describes the addition of the next nucleotide(s) in the DNA strands undergoing replication?ANucleotide X will be added to the leading strand, which is strand 1.BNucleotide Y will be added to the leading strand, which is strand 1.CNucleotide X will be added to the lagging strand, which is strand 1.DNucleotide Y will be added to the leading strand, which is strand 2.2018 / H2 / MJC PRELIM / P1 Q6QUESTION 5 Two polynucleotide strands make up a DNA molecule.What is a correct description?AThe percentage of cytosine is 50% of that of guanine in the whole molecule.BThe percentage of cytosine is the same as that of guanine in each strand.CThe percentage of cytosine is the same as that of guanine in the whole molecule.DThe percentage of cytosine is the same in each strand of the molecule.

2018 / H2 / MJC PRELIM / P1 Q12QUESTION 6Which of the following statements explain the difference in the direction in which the two strands of a DNA molecule are synthesised?1The replication of DNA is semi-conservative.2DNA polymerase can only add deoxyribonucleotides to the 3’OH group.3Each DNA molecule consists of two anti-parallel polynucleotides.4The synthesis of the lagging strand requires many more RNA primers.A 1 and 2 onlyB 2 and 3 onlyC 1, 2 and 4 only D 2, 3 and 4 only2018 / H2 / NJC PRELIM / P1 Q67Which row best describes the functions of the enzymes involved in DNA replication?unwinding of the DNA moleculesassembly of the leading strandfilling in of gaps between new DNA fragmentsfusing together of new DNA fragmentsApolymeraseligasepolymerasehelicaseBhelicasepolymerasepolymeraseligaseCligasepolymerasehelicasepolymeraseDhelicasepolymeraseligasepolymerase2018 / H2 / NYJC PRELIM / P1 Q88Francis Crick and James Watson, who published the first acceptable structure for DNA, added this statement to their account.“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”What is the specific pairing they mention for the copying mechanism now known to take place?AEach purine with either pyrimidine and each pyrimidine with either purineBEach purine with itself or the other purine and each pyrimidine with itself or the other pyrimidineCEach pyrimidine with a particular purine and each purine with a particular pyrimidineDEach pyrimidine with itself and each purine with itself

2018 / H2 / PJC PRELIM / P1 Q129During semi-conservative replication of DNA in eukaryotic cells, the following processes occur.1Free nucleotides are hydrogen bonded to those on the exposed strand.2Hydrogen bonds are broken between the complementary base pairs.3The cell receives the signal to begin to divide.4Covalent bonds form between adjacent nucleotides on the same strand.5The DNA double helix is unwound.Which shows the correct order of some of the processes?A3 → 1 → 2 → 4B3 → 2 → 4 → 5 C5 → 2 → 1 → 4D5 → 2 → 3 → 12018 / H2 / RI PRELIM / P1 Q710.The structures of purine and pyrimidine are shown below. Which of the following correctly shows the number of carbon atoms in the corresponding nucleic acid?MoleculeNumber of carbons in the moleculeADNA strand with the sequence ATCGAAA33BmRNA molecule with the sequence AUCGAAA on 1 strand30CDNA molecule with the sequence ATCGAAA on 1 strand33DDNA strand with the sequence ATCGAAA68

2018 / H2 / RVHS PRELIM / P1 Q811An unknown organism has a linear double-stranded DNA genome like that in a eukaryote. When its DNA replication was examined, it was revealed that although the process is semi-conservative, no Okazaki fragments were observed in the multiple replication forks. In addition, the end-replication problem of shortened daughter strands was not observed.Which statement correctly explains this phenomenon?AThe organism’s DNA is antiparallel.BDNA replication only starts at the 3’ end of each template strand.CDNA polymerases synthesise DNA in both 5’ to 3’ and 3’ to 5’ direction.DDNA ligases are not involved in the DNA replication process.2018 / H2 / RVHS PRELIM / P1 Q912The diagram shows the synthesis of a polynucleotide. W is a nucleoside triphosphate and the arrows indicate the location where W form bonds with the polynucleotide. Which statements are correct?1The base in W could be the purine, adenine.2The base in Y is the purine guanine.3The base in X is the pyrimidine, cytosine4The base in X could be the pyrimidine, uracil A1 and 3B2 and 3C2 and 4DAll of the above

2018 / H2 / SAJC PRELIM / P1 Q7133 different polynucleotide molecules (X, Y and Z) were isolated from a eukaryotic cell. One of them is a double-stranded DNA gene, while the other two are the pre-mRNA and mature mRNA that the DNA gene codes for.The adenine nucleotide content of all 3 molecules was examined and shown in the table below:MoleculePercentage of adenine nucleotides in the molecule / %X49Y52Z53Based on the information given, which of the following conclusions is/are valid and true?1X is definitely the DNA gene.2Z is definitely the mature mRNA.3The pre-mRNA molecule has more uracil than guanine in it.4Y has more purine nucleotides than pyrimidine nucleotides in it.A1 and 2B1, 2 and 4C1, 3 and 4D2, 3 and 4

2018 / H2 / VJC PRELIM / P1 Q614The sets of diagrams show four possible outcomes when an unlabelled molecule of DNA is allowed to replicate twice in the presence of 15N-labelled nucleotides.Labelled sections of DNA are represented by dotted lines.Which set of diagrams correctly shows the result of DNA replication?

2018 DNA Structure and