Elite Batch 2012

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Elite Dental Team

Genetics 1st

exam

<Q> Which of the following oligonucleotides forms the most stable duplex with the DNA fragment 5’GTTGACTGCA3’

<C> 5’CAACTGACGT 3 <C+> 5’TGCAGTCAAC 3’ <C> 5’CAACGGGCGT 3’ <C> 5’TGCGGGCAAC 3’ <C> 5’ACGTCAGTTG 3’

<Q> Most of the DNA in the eukaryotic nucleus is packaged in nucleosomes with

<C+> histones <C> ribonuclear proteins <C> ribosomal proteins <C> topoisomerases <C> DNA a,b proteins

<Q> To cut a double –stranded DNA molecule at the sequence- specific site AGGCCT, which enzyme should you use?

<C+> Restriction end nuclease <C> Exonuclease <C> DNase <C> phosphodiesterase <C> RNase

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<Q> A double –stranded DNA fragment contains 0.2 mole-fraction of A (adenine) . The mole-fractions of other bases G (guanine), and T (thymine) are

<C+> T=0.2, G=0.3, and C=0.3 <C> T=0.3, G=0.2, and C=0.3 <C> T=0.3, G=0.3, and C=0.2 <C> T=0.2, G=0.4, and C=0.2 <C> not possible to calculate with the information given. <Q> DNA replication originates at the indicated origin of replication. Which segment(s) serve as templates(s) for leading strand synthesis?

Origin

5’ A B 3’

3’ D

C 5’

<C> B and D

<C+> A and C

<C> A and B

<C> D

<C> B

<Q> An E.coli strain with a mutation that eliminates the AP (apurinic or apyrimidinic) endonuclease is expected to show :

<C> no change in DNA repair activity. <C> no direct repair of alkylated bases. <C> no repair of pyrimidine dimmers. <C> decreased mismatch repair activity. <C+> decreased excision repair.

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Elite Dental Team

<Q> Place the following components of the chromosome in hierarchal order starting

with the smallest component and ending with the largest.

1- solenoid

2- base pair

3- nucleosome.

4- nucleotide

5- metaphase chromosome.

6- Condensed scaffold form.

<C+> 2 < 4 < 3 < 1 < 6 < 5.

<C> 4 < 2 < 3 < 1 < 6 < 5.

<C> 2 < 4 < 3 < 6 < 1 < 5.

<C> 4 < 2 < 3 < 1 < 5 < 6.

<C> 4 < 2 < 3 < 6 < 1 < 5.

<Q> why some bases could be missed from our DNA? Because of

<C+> Acid and heat depurination.

<C> Spontaneous deaminations.

<C> Intercalating reagents

<C> UV irradiation

<C> alkylating agents.

<Q> what is the mechanism of repair in this DNA lesion?

CH3 CH3

AGGACCACCGTTGGCT

TCCTAGTGGCAACCGA

<C> Proofreading. <C+> Mismatch repair.

<C> Excision repair. <C> recombination.

<C> glycosylation.

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<Q> Which mutation in the sequence GGATCA represents a transversion?

<C+> GGATCC

<C> AGATCA

<C> GGGTCA

<C> GGACCA

<C> GGATCG

<Q> Adjacent nucleotides are joint by a :

<C> 5’-3’ phosphodiester bond <C+> 3’-5’ phosphodiester bond <C> glycosidic bond <C> deoxyribose <C> hydrogen bonds

<Q> A strain of E.coil has a mutation eliminating the 3’ to 5’ exonuclease activity of DNA Pol III. This strain is expected to show

<C+> an increased mutation frequency. <C> a decreased mutation frequency. <C> an inability to join Okazaki fragments together. <C> Continuous strand synthesis. <C> an inability to remove RNA primer.

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<Q> The DNA in a bacterium is uniformly labeled by growth for several generations on

a medium containing N15

as the sole nitrogen source. DNA isolated from these cells

bands with a higher density than DNA from cells grown on N14

(see controls above). If

the cells grown in N15

are switched to N14

- containing medium for one generations and the DNA is banded on a density gradient, what is the pattern of DNA bands expected by the mechanism responsible for DNA replication?

N15 N14 a b c d e

Controls

<C> A

<C> B I think Dr.Nabeel; finally consider C as a right answer NOT D …

<C> C

<C+> D

<C> E

<Q> The strain defective in DNA Pol I is expected to synthesize DNA

<C> Which is indistinguishable from that of the wild-type strain. <C> only in the continuous manner characteristic of the leading strand. <C+> Which retains the RNA primers in the discontinuous (lagging) strand. <C> only in the discontinuous manner characteristic of the lagging strand. <C> with a higher intrinsic error frequency.

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Elite Dental Team

<Q> Which of the following repair systems can repair the lesion shown?

T T

A A <C> mismatch repair. <C> base excision repair. <C+> nucleotide excision repair. <C> direct repair by photolyase <C> uridine glycosidase.

<Q> Which one of the following double-slandered DNA molecules has the lowest melting** temperature (Tm)?

<C> GCGCGCGC CGCGCGCG

<C> GCCATGGC CGGTACCG

<C> GGAATTCC CCTTAAGG

<C> GAAATTTC

CTTTAAAG

<C+> ATATATAT

TATATATA

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<Q> Pick the type of mutation illustrated by the following nucleotide change

Wild type ACU AGU UUA GAU UGA

Mutant* ACU AGC UUA GAU UGA

<C+> transition mutation.

<C> insertion mutation

<C> deletion mutation

<C> transversion mutation

<C> missense mutation

<Q> the order of bases from left to right

<C> U A G C T

<C> T G A C U

<C> A T C G U

<C+> T A G U C

<C> T A G C U

<Q> Concerning replication in E.coli :

<C> DNA polymerase I synthesize Okazaki fragments.

<C> polymerization of the leading strand DNA occurs 5’ 3’, but occurs

3’ 5’ on the lagging strand.

<C> DNA synthesis occurs at only one end of the replication bubble.

<C+> synthesis of the leading strand occurs continuously, while synthesis of the

lagging strand occurs discontinuously.

<C> Okazaki fragment synthesis is primed by E.coli RNA polymerase.

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Elite Dental Team

Q) The RNA associated with a fungal telomerase has the sequence 5'-CUGCUGCUGCUG-3'.

What is the repeated sequence at the telomeres in the fungus?

a. 5'(GACGAC) b. 5'(CAGCAG) c. 5'(CTGCTG) d. 5'(GTCGTC) e. 5'(GUCGUC)

Answer: b

Q) Cultured cells from three patients with Xeroderma pigmentosum (XP) were fused in

pairs and analyzed for defects in DNA repair, the cells from patient one are

designated P1, from patient two P2, and from patient three P3, the results from

these tests are shown in the table below, A “ – “ symbol indicates failure of the

fused cell pair to repair U.V - induced DNA damage and a “ + “ symbol indicates that

the fusion restores DNA repair.

Which patients apparently have defects in the same gene that in codes DNA repair Protein?

P1 P2 P3

P1 - + -

P2 + - +

P3 - + -

a. Non of the patients b. P1, P2, and P3 c. P1 and P2 d. P1 and P3 e. P2 and P3

Answer = d

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Q) 8-oxyG causes:

a. G to T transversion. b. C to G transition. c. A to G transition. d. T to G transversion.

e. A to C transversion. Answer = a

Q) Match the type of DNA damage to the mutagen effect of nitrous acid:

a. Depurination of Guanine. b. G-C to A-T transition. c. A-T to C-G transversion. d. Base insertion. e. double strands breaks.

Answer= b.

Q) What is the molecular base of Xeroderma Pigmentosum :

a. Mutations in genes involved in nucleotide excision repair b. Mutations in genes that defect DNA damage. c. Mutations in a.a DNA helicase gene. d. Mutations in mut S gene. e. Mutations in mut H gene.

Answer = a

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<Q> The base that deaminates to form thymine is:

a. Uracil. b. Inosine. c. Cytosine.

d. 5-methylCytosine. e. 5-methylGuanine.

Answer : d

Q) What is the importance of Cde-6 and Cdt-1 ?

a. They are essential for coating the DNA with MCM proteins to initiate DNA replication. b. They are essential to remove positive supercoilling during replication. c. They are essential to unwind DNA during replication. d. They are essential components for the mismatch repair system. e. They are essential catalytic proteins associated with telomerase.

Answer = a.

Q) Concerning replication in E.coli:

a. DNA polymerase I synthesizes Okazaki fragments.

b. Polymerization of the leading strand DNA occurs 3'

5' on the lagging strand. c. DNA synthesis occurs at only one end of the replication bubble.

d. Synthesis of the leading strand occurs continuously, while synthesis of the lagging strand occurs discontinuously. e. Okazaki fragments synthesis is primed by E.coli RNA polymerase.

Answer = d.

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Elite Dental Team

<Q> Concerning the catalytic properties of DNA polymerase I of E.coli:

a. 3'

5' exonuclease activity is used to proofread its own base incorporation.

b. 5'

3' exonuclease activity is used to proofread its own base incorporation. c. synthesis of DNA by “nick translation” requires an RNA primer. d. the enzyme displays unlimited processivity. e. the enzyme displays sequence specific endonuclease activity.

Answer = a.

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Q) Match the positions of the lettered arrows in the gene to the following statements locations of the 3'- flanking region:

Answer = e

Q) Identify a physiological substrate for DNA polymerase:

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Answer = a

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Q ) choose the correct answer in regard to the figure shown ?

a. The ends of both chromosomes A and B are completed by telomerase. b. The ends of both chromosomes A and B are completed by 5' - 3' polymerase activity. c.

The end of chromosome A is completed by telomerase while that of B by 5' - 3'

polymerase.

d. The end of chromosome B is completed by telomerase while that of A by 5' - 3'

polymerase.

Answer = d