1) A student inspired by Meselson and Stahl experiment want to know what happens to histones during eukaryotic DNA replication. He designed protocol whose steps are below:Step 1 : grow cells for several generations in medium that contains amino acids labeled with a heavy isotopeStep 2 : transfer the cells to a medium that contains amino acids with light isotopeStep 3 : isolate histone octamers before and after replication and subject them to density gradientcentrifugationObservation : octamer prior to replication shown single band lower in test tube while after replication octamer shown broad band but upper in position in comparison to earlier band.The correct conclusion will bea. histone followed semi-conservative model of replication like DNAb. after DNA replication, the new octamers are a random mixture of old and new histonec. new octamer and old octamer are in 1 : 1 after DNA replicationd. nothing happened to old histones, they remained intact.

2) At least 10 percent of human DNA exists as repeated multiples of relatively short sequences of nucleotides. Which of the following statements about this repetitive DNA is correct?a. much of the repetitive DNA is transcribed into messenger RNAb. repetitive DNA is largely responsible for the production of enzymes and other protein moleculesc. most repeated sequences are associated with detectable phenotypesd. highly repeated sequences rapidly reassociate in DNA hybridization studies.

3) The conformation of a nucleotide in DNA is affected by rotation about how many bonds?a. 4 b. 6 c. 7 d. 3

4) What would stop DNA replication in bacteria?P. addition of a DNA polymerase inhibitorQ. addition of dideoxyribonucleotides (ddNTP)R. addition of lamin inhibitorS. addition of actin inhibitora. P and Qb. Q and Rc. R and Sd. P and S

5) Okazaki fragments were prepared from an E.coli strain harboring pBR322 plasmid. These fragments were then hybridized to single stranded DNA molecules prepared by carefully separating the two strands of the E.coli chromosome and the plasmid. The Okazaki fragments would anneal toa. both the strands of the chromosome and the plasmidb. both the strands of the chromosome but only one strand of the plasmidc. one strand of the chromosome but both the strands of the plasmidd. one strand each of the chromosome and the plasmid

6) Which of the following covalent bond types are found in the structure of ATP?a. N-glycosidic, thioester, phosphodiesterb. phosphoanhydride, phosphomonoester, N-glycosidicc. ester, ether, phosphoanhydrided. ether, thioester, phosphomonoester

7) A nucleic acid has following base composition:A: 30 percentG: 40 percentWhat can be inferred from this data?a. the nucleic acid is a RNAb. the nucleic acid is a DNAc. the nucleic acid is two-strandedd. the nucleic acid is single-stranded

8) Which statement about the DnaB helicase are true?P. DnaB helicase is a ring-shaped molecule and the dsDNA goes through the holeQ. DnaB helicase is loaded onto the lagging strand by the clamp loaderR. DnaB is loaded onto ssDNA at oriC by DnaCS. interaction between the tau subunit of the replisome and DnaB causes the helicase to go slowerT. DnaB moves in 5’ to 3’ directiona. P and Rb. R and Tc. Q and Rd. S and T

9) Okazaki fragments are formed during DNA synthesis, becauseP. DNA synthesis extends from 5’ to 3’ directionQ. Their synthesis are opposite to the direction of replication forkR. DNA ahead of replication fork is positively supercoiledS. DNA synthesis is semi-conservativea. Q and Rb. P and Qc. R and Sd. S and P

10) Match the terms in group I with terms in group IIGroup I Group IIP. RNase-P 1. lac operonQ. Leucine zipper 2. rRNA gene transcriptionR. RNA pol-I 3. tRNA gene transcriptionS. Attenuation 4. Transcription factors 5. Ribozymes 6. trp operon 7. mRNA splicinga. P-7, Q-5, R-3, S-1b. P-4, Q-5, R-2, S-1c. P-5, Q-4, R-2, S-6d. P-4, Q-5, R-3, S-6

11) Which of the following statements about DNA polymerases are correct?(a) They add deoxyribonucleotide units to the 3„-hydroxyl of a primer.(b) They use the template strand to help choose which deoxyribonucleotide unit to add to the growing DNA chain.(c) They contain a 3„5„ nuclease that cleaves phosphodiester bonds of misincorporated deoxyribonucleotides.(d) They check the incoming deoxyribonucleotide triphosphate (dNTP) to help insure that the correct, complementary choice is made.(e) They bind one complementary dNTP and add a second complementary dNTP to initiate a new DNA chain. 1. a and b 2. a, b c and d 3. only c and d 4. a, b, c and e

12. Mg2+; serves which of the following functions in the reaction catalyzed by DNA polymerases?(a) stabilizes the pentacoordinate transition state of the phosphodiester bond formation(b) precipitates inorganic phosphate (Pi) arising from the reaction(c) interacts with the 3„-hydroxyl of the incoming dNTP(d) forms a bridge between the 3„-hyroxyl of the primer and a phosphate in the dNTP(e) stabilizes the negative charge on the departing pyrophosphate, which is derived from the incoming dNTP1. a and c2. a, c, d and e3. only d4. a, d and e

13. Which of the following statements about DNA molecules that are topoisomers are correct?(a) They are bound to topoisomerases.(b) They differ from one another topologically only in that they have different linking numbers.(c) They may be separated from one another by electrophoresis.

(d) They have identical molecular weights.(e) They are topological or spatial isomers.1. c, d and e2. b, c and d3. b, c, d and e4. a and b

14. Which of the following statements about topoisomerases are correct?(a) They alter the linking numbers of topoisomers.(b) They break and reseal phosphodiester bonds.(c) They require NAD; as a cofactor to supply the energy to drive the conversion of a supercoiled molecule to its relaxed form.(d) They form covalent intermediates with their DNA substrates.(e) They can, in the case of a particular type of topoisomerase, use ATP to form negatively supercoiled DNA from relaxed DNA in E. coli.1. a, b, c and d2. a, b and c3. a and c4. a, b, d and e

15. Which of the following statements about DNA replication in E. coli are correct?(a) It occurs at a replication fork.(b) It starts at a unique locus on the chromosome.(c) It proceeds with one replication fork per replicating molecule.(d) It is bidirectional.(e) It involves discontinuous synthesis on the leading strand.(f) It uses RNA transiently as a template.1. a, b. and d2. b, c and f3. both d and c4. a, b, c and f

16. Which of the following statements about DNA polymerase III holoenzyme from E. coli are correct?(a) It elongates a growing DNA chain hundreds of times faster than does DNA polymerase I.(b) It associates with the parental template, adds a few nucleotides to the growing chain, and then dissociates before initiating another synthesis cycle.

(c) It maintains a high fidelity of replication, in part by acting in conjunction with a subunit containing a 3„D5„ exonuclease activity.(d) When replicating DNA, it is a molecular assembly composed of at least 10 different kinds of subunits.

1. a, b and d2. a, c and d3. only d4. a, b, c and e

17. Which of the following statements about DNA ligase are correct?(a) It forms a phosphodiester bond between a 5„-hydroxyl and a 3„-phosphate in duplex DNA.(b) It requires a cofactor, either NAD; or ATP, depending on the source of the enzyme, to provide the energy to form the phosphodiester bond.(c) It catalyzes its reaction by a mechanism that involves the formation of a covalently linked enzyme adenylate.(d) It catalyzes its reaction by a mechanism that involves the activation of a DNA phosphate through the formation of a phosphoanhydride bond with AMP.(e) It is involved in DNA replication, repair, and recombination.1. both d and e2. only a3. b, c, d and e4. a, b and c

18. In semiconservative replication of DNA,a. the original double helix remains intact and a new doublehelix forms.b. the strands of the double helix separate and act as templatesfor new strands.c. polymerization is catalyzed by RNA polymerase.d. polymerization is catalyzed by a double helical enzyme.e. DNA is synthesized from amino acids.

19. Which of the following does not occur during DNA replication?a. Unwinding of the parent double helixb. Formation of short pieces that are connected by DNA ligasec. Complementary base pairing

d. Use of a primere. Polymerization in the 3′-to-5′ direction

20. One strand of DNA has the sequence 5′−ATTCCG−3′. The complementary strand for this isa. 5′−TAAGGC−3′b. 5′−ATTCCG−3′c. 5′−ACCTTA−3′d. 5′−CGGAAT−3′e. 5′−GCCTTA−3′

21. The role of DNA ligase in DNA replication is toa. add more nucleotides to the growing strand one at a time.b. open up the two DNA strands to expose template strands.c. ligate base to sugar to phosphate in a nucleotide.d. bond Okazaki fragments to one another.e. remove incorrectly paired bases.

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24. Which one of the following DNA polymerase is essential for both the replication and repair of DNA?(a) DNA polymerase I (b) DNA polymerase II(c) DNA polymerase III (d) DNA polymerase d

25. Which of the following processes does not take place in the 5′→3′ direction?1. DNA replication2. Transcription3. Nick translation4. RNA editing

27. A culture of E. coli growing in a medium containing15NH4Cl is switched to a medium containing 14NH4Cl for three generations (an eightfold increase in population). What is the molar ratio of hybrid DNA (15N–14N) to light DNA (14N–14N) at this point?1. 0.332. 0 .603. 0.804. 1.0

26. DNA repair, synthesis and recombination are intimately connected and inter dependent. An apparent commonality between processes of DNA replication and repair in the enzymatically catalyzed synthesis of DNA polynucleotide segments, which can be assembled with preexisting polynucleotides, leading to repair or replication. Synthesis ofthese polynucleotide segments is catalyzed by a group of enzymes DNA-dependant DNA polymerases. In the case of E.coli, DNA polymerase has been isolated in three distinct forms whereas five main types of polymerase have been isolated from mammalian cells. All the polymerases synthesize polynucleotides only in the 5' 3' direction. If polynucleotide chains could be elongated in 3’ 5' direction, the hypothetical growing 5' terminus, rather than the incoming nucleotide, would carry a triposphate that is unsuitable for further elongation. The 3' 5’ exonuclease activity is not associated with all the polymerases and only present in(A) All E. coli DNA polymerases but not all mammalian polymerases.(B) Pol I, Pol II, Pol III, Pol α, Pol β.

(C) Pol I, Pol II, Pol δ, Polε, Pol γ(D) Pol I, Pol II, Polα, Polε .The correct statements are1. (A) and (B).2. (A), (B) and (C).3. (A) and (C).4. (A), (C) and (D).

28. Deletion of the leader sequence of trp operon of E. coli would result ina. decreased transcription of trp operonb. increased transcription of trp operonc. no effect on transcriptiond. decreased transcription of trp operon in the presence of tryptophan

29. Expression in poor amount and inactive form of a eukaryotic protein from eukaryotic gene in Escherichia coli using its expression vector is due toP. the absence of capping mechanism of mRNAQ. codon biasR. absence of polyadenylationS. absence of proper glycosylationa. P, Qb. Q, Rc. Q, Sd. P, S

30. If E. coli bacteria are grown in the absence of both glucose and lactose, which of the following events will occur?P. the lac repressor will bind to the operator sequenceQ. the CAP (catabolite gene activator protein) will activate transcriptionR. RNA polymerase holoenzyme will bind to the lac promoter and form open complexS. the lac operon will be transcriptionally activea. only Pb. only Qc. P and Rd. Q and S

31. Which of the statements are correct? SpliceosomesP. are composed of RNA and proteinQ. recognize RNA sequences that signal for removal of intronsR. can produce different mRNA molecules by splicing at alternate siteS. mediates splicing of group I intronsa. P and Qb. P, R and Sc. P, Q and Rd. P, Q, R and S

32. Which of the following are the mechanism of action of antibiotics?P. interfere with bacterial cell wall synthesisQ. inhibit bacterial transcription of DNAR. inhibit translation of bacterial mRNAS. change the permeability of plasma membranea. P and Qb. R and Sc. P, Q and Rd. P, Q, R and S

33. A mutant of E.coli was found which did not synthesize β-galactosidase in the presence as well as in the absence of the inducer, IPTG. The investigation revealed that the structural genes of the lac operonwere unaltered in the mutant, but one of the controlling genes (I or O) was mutated. The different allelic forms of the regulator gene and the operator gene are as follows:I+-wild type regulator geneIc-Constitutive regulatorIs-Repressor form which is insensitive to inducerO+-Wild type operator geneOc-Constitutive operatorWhich of the following mutation in the controlling genes was responsible for the above mentioned behaviour of the E.coli mutant?a. I+O+b. Ic O+c. Is O+d. I+ Oc

34. Which combination of the following statements with regard to gene expression is true?P. Heteronuclear RNA represents contiguous segment of genomic DNAQ. UTRs are part of heteronuclear RNA but not of mRNAR. UTRs are part of exonsS. Translation start codon must be in the first exona. P - true, Q - false, R - false, S - falseb. P - true, Q - false, R - true, S - falsec. P - true, Q - true, R - false, S - trued. P - false, Q - true, R - true, S – true

35. Match the subunit of the RNA polymerase of E. coli in the left column with its putative function during catalysis from the right column.(a) α (1) binds the DNA template(b) β (2) binds regulatory proteins and sequences(c) β′ (3) binds NTPs and catalyzes bond formation(d) σ70 (4) recognizes the promoter and initiates synthesis1.a-2, b-3, c-1, d-42. a-2, b-3, c-4, d-13. a-4, b-3, c-1, d-54. a-2, b-4, c-3, d-1

36) Which of the following statements about E. coli promoters are correct?(a) They may exhibit different transcription efficiencies.(b) For most genes they include variants of consensus sequences.(c) They specify the start sites for transcription on the DNA template.(d) They have identical and defining sequences.(e) They are activated when C or G residues are substituted into their −10 regions by mutation.(f) Those that have sequences that correspond closely to the consensus sequences and are separated by 17 base pairs are very efficient.1. a, b, d, and, f2. a, b, c and f3. only a and b4. a, b, c, d

37. The sequence of a duplex DNA segment in a DNA molecule is5′-ATCGCTTGTTCGGA-3′3′-TAGCGAACAAGCCT-5′When this segment serves as a template for E. coli RNA polymerase, it gives rise to a segment of RNA with the sequence 5′-UCCGAACAAGCGAU-3′Which of the following statements about the DNA segment are correct?(a) The top strand is the coding strand.(b) The bottom strand is the sense strand.(c) The top strand is the template strand.(d) The bottom strand is the antisense strand.1. only A2. both b and c3. a, b, c and d4. only d

38. Which of the following statements about the σ subunit of RNA polymerase are not correct?(a) It enables the enzyme to transcribe asymmetrically.(b) It confers on the core enzyme the ability to initiate transcription at promoters.(c) It decreases the affinity of RNA polymerase for regions of DNA that lack promoter sequences.(d) It facilitates the termination of transcription by recognizing hairpins in the transcript.1. a and b2. a, b, and c3 both c and d4 only d

39. Which of the following statements about the ρ protein of E. coli are correct?(a) It is an ATPase that is activated by binding to single-stranded DNA.(b) It recognizes specific sequences in single-stranded RNA.(c) It recognizes sequences in the DNA template strand.(d) It causes RNA polymerase to terminate transcription at template sites that are different from those that lead to r-independent termination.(e) It acts as a RNA–DNA helicase.1. a, b and c2. both d and e3. c, d and e

4. both a and e

40. Which of the following statements about eukaryotic mRNAs are correct?(a) They are derived from larger RNA precursors.(b) They result from extensive processing of their primary transcripts before serving as translation components.(c) They usually have poly(A) tails at their 5′ ends.(d) They have a cap at their 3′ ends.(e) They are often encoded by noncontiguous segments of template DNA.1.a, b, and e2. only a3. both d and e4. both c and d

41. Which of the following statements about enhancers are correct?(a) They function as promoters.(b) They function when in either orientation in the DNA.(c) They function when on either side of the activated promoter.(d) They function even when located many base pairs away from the promoter.(e) They function only in specific types of cells.1. only b2. a, b. c, d and e3. b, c d, and e4. bith c and d

42. Which of the following are important sequence elements in the splicing reactions that produce eukaryotic mRNAs?(a) exon sequences located between 20 and 50 nucleotides from the 5′ splice site(b) exon sequences located between 20 and 50 nucleotides from the 3′ splice site(c) intron sequences located between 20 and 50 nucleotides from the 5′ splice site(d) intron sequences located between 20 and 50 nucleotides from the 3′ splice site(e) intron sequences at the 5′ splice site(f) intron sequences at the 3′ splice site1. d. e and f2. only b

3. a,d and e4.both a and e

43. Eukaryotic mRNA splicing involves which of the following?(a) the formation of 2′ 5′ phosphodiester bonds(b) a sequence-specific endoribonuclease that hydrolyzes the phosphodiester bond at the junctions of the intron with the exon(c) the spliceosome(d) the coupling of phosphodiester bond formation to ATP hydrolysis(e) the formation of lariat intermediates1.both a and b2. a, b and e3. only c4. a, c and e

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59. In zinc finger proteins, the amino acid residues that coordinate zinc are(A) Cys and His (B) Asp and Glu (C) Arg and Lys (D) Asp and Arg

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