Question 1

The form of DNA with 34 Å pitch with a rise per base pair of 3.4 Å is called

Accepted Answer

Each strand appears like a helical staircase. Each step of ascent is represented by a pair of bases. At each step of ascent, the strand turns the pitch would be 34 Å. The rise per base pair would be 3.4 Å. This form of DNA with the above mentioned salient features is called B-DNA.

Question 2

According to Watson-Crick model, DNA exists as a …A… . The two strands of polynucleotides are …B… . The backbone is formed by the  …C…, …D… chain. The nitrogen bases are more or less …E… to this backbone.Choose the correct options for the blanks A, B, C, D and E

Accepted Answer

A-double helix, B-antiparallel, C-phosphate, D-sugar, E-perpendicular. In Watson and Crick's model, the two strands of the DNA double helix are held together by hydrogen bonds between nitrogenous bases on opposite strands. Each pair of bases lies flat, forming a "rung" on the ladder of the DNA molecule. Base pairs aren't made up of just any combination of bases.

Question 3

Assertion : Comparative biochemistry provides a strong evidence in favour of common ancestory of living beings.
Reason : Genetic code is universal.

Accepted Answer

Comparative biochemistry provides a strong evidence for common ancestors of living beings (e.g. proteins lymph, enzymes, hormones, blood groups etc.)

Question 4

Which purine base is found in RNA?

Accepted Answer

The bases are of two types-purines and pyrimidines. The purine derivatives adenine (A) and guanine (G) are double ring structures whereas pyrimidine derivatives thymine, cytosine and uracil are single ring structures. Thymine (T) and cytosine (C) are found in DNA and cytosine (C) and uracil (U) is found in RNA.

Question 5

Which of the following nucleotide sequences contains 4 pyrimidine bases?

Accepted Answer

In the given question there are 4 pyrimidines as 2 cytosine and 2 thymine in option ' a '.

Question 6

In RNA, thymine is replaced by

Accepted Answer

In RNA, thymine is replaced by uracil.

Question 7

The basic unit of nucleic acid is

Accepted Answer

The nucleic acids (DNA and RNA) are the molecules having complex structure and very high molecular weights. The nucleic acid is composed of a large number of nucleotide molecules joined into a linear, unbranched chain. 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 8

RNA does not possess

Accepted Answer

RNA does not possess thymine.

Question 9

Which is wrong about nucleic acids?

Accepted Answer

One complete turn of a DNA double helix is 34A˚ long and has 10 base pairs.

Question 10

Assertion : Comparative biochemistry provides a strong evidence in favour of common ancestory of living beings. Reason : Genetic code is universal.

Accepted Answer

Comparative biochemistry provides a strong evidence for common ancestors of living beings (e.g. proteins lymph, enzymes, hormones, blood groups etc.)

Question 11

Assertion : DNA molecules and RNA molecules are found in the nucleus of cell. Reason : On heating, enzymes do not lose their specific activity.

Accepted Answer

We know that DNA molecules are found primarily in the nucleus of the cell but RNA molecules are found outside the nucleus. By heating, its special structural arrangement is changed irreversibly. This results in the conversion of enzyme into a fibrous or insoluble form. Due to this irreversible change, enzymes lose their specific activity when heated.

Question 12

Assertion: The heterocyclic compounds in nucleic acid are the nitrogenous bases. Reason : Adenine and guanine are substituted pyrimidines while uracil, cytosine and thymine are substituted purines.

Accepted Answer

Nucleic acids are polynucleotides. A nucleotide has three chemically distinct components. One is a heterocyclic compound, the second is a monosaccharide and the third a phosphoric acid or phosphate. The heterocyclic compounds in nucleic acids are the nitrogenous bases named adenine, guanine, uracil, cytosine and thymine. Adenine and guanine are substituted purines while the rest are substituted pyrimidines formed from the skeletal heterocyclic rings purine and pyrimidine respectively.

Question 13

Name the heterocyclic compounds, which are known as nitrogenous bases. Choose the most appropriate option.

Accepted Answer

Adenine, guanine, uracil, cytosine and thymine

Question 14

Those nucleic acids, which behave like enzymes are known as

Accepted Answer

Those nucleic acids, which behave like enzymes are known as ribozymes.

Question 15

Purines and pyrimidines polymerise to form

Accepted Answer

Purines and pyrimidines polymerise to form nucleic acid.

Question 16

Nucleic acids exhibit secondary structure, justify with example.

Accepted Answer

Nucleic acids are polymeric macromolecules or large biological molecules, essential for all known forms of life. The secondary structure of a nucleic acid molecule refers to the base pairing interactions within a single molecule or set of interacting molecules. DNA and RNA represent two main nucleic acids, however their secondary structures differ e.g., the secondary structure of DNA comprises of two complementary strands of polydeoxyribonucleotide, spirally coiled on a common axis forming a helical structure.This double helical structure of DNA is stabilised by phosphodiester bonds (between 5' of sugar of one nucleotide and 3 of sugar of another nucleotide), hydrogen bonds (between bases, i.e., hydrogen of one base and nitrogen of oxygen of other base) and ionic interactions.

Question 17

In RNA, thymine is replaced by

Accepted Answer

(d) RNA is a single chain of ribonucleotides. Each ribonucleotide consists of nitrogenous bases (adenine, guanine, cytosine and uracil), ribose sugar and phosphoric acid.

Question 18

Length of one turn of the helix in a B-form DNA is approximately

Accepted Answer

Length of one turn of DNA helix is 34Å.1Å = 10–1  nm

Question 19

Read the following four statements (A to D) and mark the option that has both correct statements A. Blood conc. of glucose in a normal healthy man is 4.5 to 5.0 mM B. In proteins only left handed helices are observed C. The pitch of B- DNA is 3.4 Angstrom D. At each step of ascent the strand of DNA turns 36 degree

Accepted Answer

(d) In proteins, only right handed helices are observed.The pitch of B- DNA is 34 Angstrom

Question 20

According to Watson and Crick model of DNA

Accepted Answer

Both options (a) and (b) are correct with respect to the structure of DNA elucidated by Watson and Crick.Option (c) is incorrect and can be corrected as The backbone of DNA is formed by the sugar phosphate chain.

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