Unit 3: Structure of Nucleic Acids; DNA Packaging and Replication - Practice Quiz

1 Which form of DNA is the most common and biologically predominant right-handed double helix under physiological conditions?

2 In the DNA double helix, adenine (A) pairs with thymine (T) through how many hydrogen bonds?

3 Which unusual form of DNA has a left-handed helical structure with a zig-zag sugar-phosphate backbone?

4 According to Chargaff's rule, in double-stranded DNA the amount of adenine equals the amount of which base?

5 The temperature at which half of the DNA molecules become single-stranded during denaturation is called the:

6 DNA with a higher G–C content will have a melting temperature () that is:

7 The process by which separated complementary DNA strands come back together to reform a double helix is called:

8 Which enzyme is responsible for relieving supercoiling tension in DNA?

9 When DNA is coiled in the direction opposite to that of the right-handed helix, it is said to be:

10 Which type of RNA carries amino acids to the ribosome during protein synthesis?

11 In RNA, which nitrogenous base replaces thymine found in DNA?

12 Which type of RNA is the most abundant in the cell and forms a structural part of ribosomes?

13 Histone proteins are rich in which type of amino acids, giving them a positive charge?

14 Which histone protein acts as a linker histone rather than a core histone?

15 The core of a nucleosome is composed of a histone octamer containing how many histone molecules?

16 Which enzyme unwinds the DNA double helix at the replication fork?

17 Which enzyme joins Okazaki fragments together by forming phosphodiester bonds?

18 Which DNA polymerase is the main enzyme responsible for synthesizing new DNA strands in prokaryotes like E. coli?

19 In eukaryotic DNA replication, the ends of linear chromosomes are maintained by which enzyme?

20 The proofreading ability of DNA polymerase that removes incorrectly added nucleotides is due to its:

21 A DNA sample is found to be a left-handed double helix with a zig-zag sugar-phosphate backbone and about 12 base pairs per turn. Which conformation does this sample most likely represent?

22 In a segment of double-stranded DNA, adenine constitutes 30% of the total bases. Applying Chargaff's rules, what is the percentage of guanine?

23 Two DNA samples of equal length are heated. Sample X has a higher melting temperature () than sample Y. What can be concluded about sample X?

24 During DNA renaturation experiments, the rate of reassociation is often expressed using the value. A DNA with highly repetitive sequences will show which behaviour?

25 A circular DNA molecule has a linking number lower than that of its relaxed form. This molecule is best described as:

26 Which enzyme relieves positive supercoils that build up ahead of a replication fork by introducing negative supercoils in bacteria?

27 A researcher isolates an RNA molecule containing an anticodon loop, a T\u03a8C loop, and a D-loop arranged in a cloverleaf secondary structure. Which type of RNA is this?

28 In eukaryotic cells, which RNA type is the most abundant by mass and forms the catalytic core of the ribosome?

29 Which property of histone proteins allows them to bind tightly to DNA?

30 Which histone is NOT part of the nucleosome core octamer but instead binds to linker DNA?

31 Approximately how many base pairs of DNA are wrapped around a single histone octamer core to form the nucleosome core particle?

32 The 'beads-on-a-string' appearance of chromatin under the electron microscope corresponds to which level of packaging?

33 Why is a primer required for DNA polymerase to begin synthesizing a new strand?

34 What is the primary role of single-strand binding (SSB) proteins during replication?

35 In E. coli, which enzyme removes the RNA primers and replaces them with DNA during replication?

36 During replication of the leading and lagging strands, the lagging strand is synthesized discontinuously because:

37 Which feature distinguishes eukaryotic chromosomal replication from prokaryotic replication?

38 The enzyme telomerase is required in eukaryotes to solve which specific problem of linear chromosome replication?

39 Which activity of DNA polymerase III immediately corrects a mismatched nucleotide during synthesis?

40 In rolling circle replication, what is the initial event that starts the process on the circular template?

41 A DNA sample is analyzed and found to have a helical repeat of 12 base pairs per turn, a left-handed helix, and a zig-zag sugar-phosphate backbone. Under high salt conditions, alternating purine-pyrimidine sequences favor this form. Which conformation and driving factor combination is correct?

42 Two DNA samples have identical length but sample X melts at and sample Y at under identical buffer conditions. What can be reliably concluded about sample Y relative to X?

43 In a (renaturation kinetics) experiment on a eukaryotic genome, three distinct components reassociate at different values. The fraction reassociating at the lowest most likely represents:

44 A relaxed circular DNA has . After the action of an enzyme, becomes 490 while the molecule is kept under conditions favoring -form. Assuming no change in twist (), what is the writhe and the type of supercoiling?

45 Which statement correctly distinguishes the ATP requirements and topological outcomes of bacterial topoisomerase I and DNA gyrase (topoisomerase II)?

46 A tRNA molecule loses its ability to be recognized by its cognate aminoacyl-tRNA synthetase after a point mutation, yet its cloverleaf secondary structure and anticodon are unchanged. The most likely explanation is a mutation affecting:

47 Ribosomal RNA is often described as the catalytic component of the ribosome. Which observation most directly supports rRNA (not ribosomal protein) as the peptidyl transferase catalyst?

48 Histone H1 differs functionally from core histones in chromatin organization. Which statement best captures its distinct structural role?

49 During replication-coupled nucleosome assembly, histones are deposited in a defined order onto newly synthesized DNA. What is the correct sequence and its functional rationale?

50 In E. coli, a temperature-sensitive mutation inactivates the (tau) subunit of the DNA polymerase III holoenzyme at the restrictive temperature. What is the most direct consequence?

51 A researcher observes that in the absence of a particular protein, Okazaki fragments accumulate as short primed segments that are never joined, and RNA primers persist. Which combined defect best explains this?

52 In the E. coli origin oriC, replication initiation is tightly regulated. Which mechanism prevents immediate re-initiation at newly replicated origins?

53 Bidirectional replication from a single origin on a circular bacterial chromosome terminates in a specific region. What is the role of the Tus-Ter system?

54 Eukaryotic origins fire only once per cell cycle. Which regulatory logic involving the pre-replication complex (pre-RC) enforces this?

55 The end-replication problem in linear eukaryotic chromosomes arises specifically because:

56 Overall replication fidelity in E. coli approaches 1 error per – bp. If base selection gives , proofreading adds , what approximate contribution must mismatch repair provide to reach an overall error rate of ?

57 In E. coli methyl-directed mismatch repair, how does the system correctly identify and excise the newly synthesized (error-containing) strand rather than the template?

58 During rolling circle replication (e.g., of X174 or F plasmid transfer), what event initiates the process and generates the free 3'-OH used for leading-strand extension?

59 A rolling circle intermediate produces a single-stranded linear tail that is many genome-lengths long (a concatemer). What downstream processing is required to yield unit-length genomes, as seen in some bacteriophages?

60 Chargaff's rules state and for double-stranded DNA. In a single strand of a given DNA, and . What are the percentages of T and C in the complementary strand?