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