NEET : Multiple Choice questions: Structure of DNA

1. Consider the following statement and select the correct code:

1.Francis Crick and James Watson proposed the double helix model of DNA.
2.They gave  double helix model of DNA on the basis of X ray diffraction data given by Wilkins and Franklin.
A. Only 1 

B. Only 2

C. Both 1 and 2

D. Neither 1 nor 2

Answer: C Explanation 

2. Which of the following statement is not correct.

A. DNA is made up of two Polynucleotide chain.

B.Both strands of DNA are coiled in a right handed fashion.

C. One turn of DNA helix has 10 base pairs.

D. Above features are related to Z DNA.

Answer:D Explanation

3. The Backbone of DNA is made up of 

A. Nitrogenous base & Sugar

B. Phosphate and Sugar

C.Nitrogenous base & phosphate

D. Nitrogenous base, Sugar and Phosphate

Answer:B Explanation

4. Which of the following statement is not correct about the nitrogenous base in DNA.

A. Adenine always joins with guanine whereas Cytosine joins with thymine.

B. Adenine and Guanine are purine whereas Thymine and Cytosine are pyrimidine.

C. There are two hydrogen bond between adenine and thymine.

D. There are three hydrogen bond between Cytosine and Guanine.

Answer: A  Explanation

5. The pitch of DNA helix is
A. 3.4nm        B. 2.4 nm

C. 4.5 nm.      D. 4.3 nm

Answer:A Explanation

6. The Distance between two base pairs of DNA helix is

A. 0.34 nm      B. 3.4nm

C. 0.24 nm      D. 2.4nm

Answer: A Explanation

7. Which of the following statement is not correct.

A. DNA Is made up of two linear strands that run opposite to each Other or anti-parallel.

B. Each DNA strand is made up of smaller units called nucleotides

C. Both strands of DNA have opposite polarity. One strand has polarity from 5' to 3' and the other strand has polarity from 3' to 5'

D. Back bone of DNA is made up of Nitrogenous base and Phosphate.

Answer:D Explanation

8. Which of the following chemical bond is present between the nitrogenous base in DNA.

A. Hydrogen bond

B. Glycosidic bond

C. Peptide bond 

D. Sulphide bonds

Answer:D Explanation

9. Who of the following stated that In double strand DNA the ratio between adenine and thymine , and cytosine and guanine is always equal to one or constant.

A. Erwin chargaff

B. Francis crick

C. James Watson 

D. None of the above 

Answer: A Explanation

10. According to Erwin chargaff :

A. A/T =G/C =1

B. A/T x G/C =1

C. A/T + G/C =1

D. A/T ÷ G/C =1

11. If A double strand DNA has 1800 nucleotides. Out of these 700 are adenine. Calculate the numbers of guanine in DNA.

A. 300           B. 700

C. 1800.         D. 2500

Answer: A Explanation