Q: Which of the following is incorrect?<b

Adenylic acid is not a nucleoside, it is a nucleotide.

Q: A in the given structure represents-

A is ester bond formed by condensation reactions, involving elimination of water.

Q: One strand of DNA has sequence of nucleotide 3' ATTCGCTAT 5' then other strand of DNA has

In a double stranded DNA, the sequence of nucleotides is complementary to each other, i.e., A pair with T and G pair with C. So, the sequence of nucleotide for 3 ' ATTCGCTAT 5 ' will be 5 ' TAAGCGATA 3 '.

Q: One turn of DNA has nucleotide pairs

These are five forms of DNA, B-DNA is most common.A-DNA – 11 pairsB-DNA – 10 pairsC-DNA – 9.33 pairsD-DNA – 8 pairsZ-DNA – 12 pairs

Q: If the total amount of adenine and thymine in a double-stranded DNA is 60%, then the amount of guanine in this DNA will be

Purine and pyrimidine nitrogenous base are found in DNA. Among purines, adenine pairs only with the pyrimidine thymine. Similarly, guanine pairs with the cytosine. The fact that total amount of purine will be equal to total amount of pyrimidine was first enunciated by Chargaff in 1950. From this law,Adenine=Thymine=60/2=30%Guanine=Cytosine=40/2=20%

Q: Which of the following radioisotope is not suitable for DNA labeling based studies?

S35 radioisotope is not suitable for DNA labelling based studies as DNA does not contain sulphur. S35 radioisotope is suitable for protein labeling based studies because protein contains sulphur.

Question 1

Nucleotides are formed by

Accepted Answer

The nucleotide is formed by the union of a phosphate group with a nucleoside. A nucleoside contains a sugar molecule along with an organic nitrogenous base. Thus, a nucleotide contains a organic nitrogenous base (purine or pyrimidine) along with a sugar molecule and a phosphate group,                     Nucleoside=Sugar molecule+Organic nitrogenous base.Nucleotide=Nucleoside+Phosphate group

Question 2

Select the correct pair of substituted purines

Accepted Answer

Adenine and guanine are substituted purines, while the rest (uracil, cytosine and thymine) are substituted pyrimidines.

Question 3

For nucleic acids, the building block is a

Accepted Answer

For nucleic acids, the building block is a nucleotide. A nucleotide has three chemically distinct components. One is a heterocyclic compound, second is a monosaccharide and third is phosphoric acid or phosphate.

Question 4

‘G’ in DNA strand base pairs with ‘C’ by 3… bonds

Accepted Answer

A and G of one strand compulsorily base pairs with T and C, respectively, on the other strand. There are two hydrogen bonds between A and T and three H-bonds between G and C.

Question 5

Which of the following is incorrect?<b

Accepted Answer

Adenylic acid is not a nucleoside, it is a nucleotide.

Question 6

A in the given structure represents-

Accepted Answer

A is ester bond formed by condensation reactions, involving elimination of water.

Question 7

One strand of DNA has sequence of nucleotide 3' ATTCGCTAT 5' then other strand of DNA has

Accepted Answer

In a double stranded DNA, the sequence of nucleotides is complementary to each other, i.e., A pair with T and G pair with C. So, the sequence of nucleotide for 3 ' ATTCGCTAT 5 ' will be 5 ' TAAGCGATA 3 '.

Question 8

One turn of DNA has nucleotide pairs

Accepted Answer

These are five forms of DNA, B-DNA is most common.A-DNA – 11 pairsB-DNA – 10 pairsC-DNA – 9.33 pairsD-DNA – 8 pairsZ-DNA – 12 pairs

Question 9

If the total amount of adenine and thymine in a double-stranded DNA is 60%, then the amount of guanine in this DNA will be

Accepted Answer

Purine and pyrimidine nitrogenous base are found in DNA. Among purines, adenine pairs only with the pyrimidine thymine. Similarly, guanine pairs with the cytosine. The fact that total amount of purine will be equal to total amount of pyrimidine was first enunciated by Chargaff in 1950. From this law,Adenine=Thymine=60/2=30%Guanine=Cytosine=40/2=20%

Question 10

Which of the following radioisotope is not suitable for DNA labeling based studies?

Accepted Answer

S35 radioisotope is not suitable for DNA labelling based studies as DNA does not contain sulphur. S35 radioisotope is suitable for protein labeling based studies because protein contains sulphur.

Question 11

Which statement is true?

Accepted Answer

Nucleotides contain carbon, hydrogen, oxygen, nitrogen and phosphorous. Nucleotides are either purines or pyrimidines. Adenine and guanine are the two purines which are the 9 -membered double ringed compound where each ring possesses four nitrogen atoms. Thymine, uracil, and cytosine are the pyrimidines which are single ringed nitrogenous compounds.

Question 12

Which of the following is formed by deamination of Adenine

Accepted Answer

Hypoxanthine is formed by Deamination of Adenine. In deamination, amine group is removed from the molecule. Deamination of adenine by HNO2​ and UV rays produces hypoxanthine. It makes hydrogen bonds with cytosine rather than with thymine.

Question 13

5 -bromouracil base is analogous to

Accepted Answer

Base pairing is followed up by the bonding through a common hydrogen bond. Base analogs have an almost similar structure to one of the four nitrogenous bases of DNA named as adenine, thymine, cytosine, or guanine).

Question 14

Assertion: The bonds attaching second and third phosphate in higher nucleotide are high energy bonds.
Reason: The bonds are attached against force of repulsion.

Accepted Answer

Nucleotides which possess more than one phosphate group are called higher nucleotides. The second and third phosphates of higher nucleotides are attached against forces of repulsion between similarly charged phosphate radicals. Hence, the bonds attaching second and third phosphates are higher energy bonds.

Question 15

The given diagrammatic representation shows one of the categories of small molecular weight organic compounds in the living tissues. Identify the category shown and the one blank component "X " in it.Category               Component

Accepted Answer

The given structure corresponds with the structure of ribose sugar. As it lacks a phosphoric acid hence it can be a nucleoside not a nucleotide.

Question 16

Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by

Accepted Answer

Each nucleotide consists of three distinct units - a phosphate group derived from phosphoric acid, a pentose sugar and a ring shaped nitrogenous base. Nucleoside + Phosphoric acid → Nucleotide +H2​O

Question 17

A nucleotide is formed of

Accepted Answer

(c) : Nucleotide is an organic compound consisting of a nitrogen-containing purine or pyrimidine base linked to a sugar (ribose or deoxyribose) and a phosphate group.

Question 18

DNA is composed of repeating units of

Accepted Answer

DNA is the largest macromolecule in the organisms. It is a long, double chain of deoxyribonucleotide or deoxyribotide units. The two deoxyribonucleotide chains are twisted around a common axis to form a right-handed double helix (spiral) that encloses a cylindrical space in it. Each deoxyribonucleotide unit, in turn, consists of three different molecules : phosphate, (PO43​−), a 5-carbon deoxyribose sugar (C5​H10​O4​) and a nitrogenous base.

Question 19

A segment of DNA has 120 adenine and 120 cytosine bases. The total number of nucleotides present in the segment is

Accepted Answer

(d): According to Chargaff's rules, the amount of adenine is always equal to that of thymine and the amount of guanine is always equal to that of cytosine i.e., A=T(120) and G=C(120), therefore, the total number of nucleotides would be 120×4=480.

Question 20

Which is not consistent with double helical structure of DNA?

Accepted Answer

The density of DNA decreases on heating as hydrogen bonds breakdown. According to Chargaff's rules, the amount of adenine is always equal to that of thymine and the amount of guanine is always equal to that of cytosine i.e A=T and G=C. The base ratio A+T/G+C may vary form species to species, but is constant for a given species.

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