DNA Structure Quiz - CBSE Class 12 Biology

Free practice quiz: DNA Structure (CBSE Class 12 Biology). 19 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. What is the basic building block of DNA?

   1. Amino acid
   2. Nucleotide
   3. Fatty acid
   4. Simple sugar
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   Answer: B. Nucleotide

   The basic building block of DNA is the nucleotide, which consists of a sugar, a phosphate group, and a nitrogenous base.

2. Which nitrogenous base pairs with adenine in DNA?

   1. Thymine
   2. Cytosine
   3. Guanine
   4. Uracil
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   Answer: A. Thymine

   In DNA, adenine pairs with thymine via two hydrogen bonds, forming base pairs.

3. Which enzyme is responsible for unwinding DNA during replication?

   1. DNA polymerase
   2. Helicase
   3. Ligase
   4. Primase
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   Answer: B. Helicase

   Helicase is the enzyme responsible for unwinding the DNA double helix during replication.

4. How many base pairs are in a complete turn of the DNA double helix?

   1. 10
   2. 12
   3. 15
   4. 20
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   Answer: A. 10

   In a complete turn of the DNA double helix, there are approximately 10 base pairs.

5. What is the function of telomeres in DNA?

   1. To replicate DNA
   2. To protect chromosome ends
   3. To produce RNA
   4. To join nucleotide strands
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   Answer: B. To protect chromosome ends

   Telomeres are repetitive sequences at the ends of chromosomes that protect them from degradation.

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