Molecular Basis of Inheritance – DNA Replication, Genetic Code, Gene Expression Quiz - ICSE Class 12 Biology

Free practice quiz: Molecular Basis of Inheritance – DNA Replication, Genetic Code, Gene Expression (ICSE Class 12 Biology). 39 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. During DNA replication, the enzyme that catalyzes the formation of phosphodiester bonds between nucleotides is:

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

   DNA polymerase is the primary enzyme responsible for synthesizing new DNA strands by adding nucleotides and forming phosphodiester bonds. Helicase unwinds the DNA, ligase seals nicks, and topoisomerase relieves supercoiling.

2. The term 'antiparallel' in the context of DNA structure refers to:

   1. The complementary base pairing between strands
   2. The sugar-phosphate backbone running in opposite directions
   3. The double helical structure
   4. The presence of two strands
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   Answer: B. The sugar-phosphate backbone running in opposite directions

   Antiparallel means that the two strands of the DNA double helix are oriented in opposite directions with respect to their 5' and 3' ends. One strand runs 5' to 3', while the complementary strand runs 3' to 5'.

3. Which of the following DNA sequences would be recognized by a restriction enzyme that recognizes the palindromic sequence 5'-GAATTC-3'?

   1. 5'-CTTAAG-3'
   2. 5'-TTAAGC-3'
   3. 5'-AGCTAG-3'
   4. 5'-CATGCATG-3'
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   Answer: A. 5'-CTTAAG-3'

   A palindromic sequence reads the same forwards on one strand as it does backwards on the complementary strand. The complementary strand to 5'-GAATTC-3' is 3'-CTTAAG-5'. When read in the 5' to 3' direction, the complementary strand is 5'-CTTAAG-3'. Therefore, the sequence 5'-CTTAAG-3' is the reverse complement of 5'-GAATTC-3', and a restriction enzyme recognizing GAATTC would also recognize CTTAAG on the opposite strand.

4. The promoter region in a gene:

   1. Is the site where transcription terminates.
   2. Is the site where the repressor protein binds.
   3. Is the site where RNA polymerase binds to initiate transcription.
   4. Codes for a structural protein.
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   Answer: C. Is the site where RNA polymerase binds to initiate transcription.

   The promoter is a regulatory DNA sequence located upstream of the coding sequence of a gene. It serves as the binding site for RNA polymerase and other transcription factors, initiating the process of transcription.

5. The genetic code is redundant. This means:

   1. Most amino acids are specified by only one codon.
   2. All codons specify amino acids.
   3. Some amino acids are specified by more than one codon.
   4. The code is not universal.
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   Answer: C. Some amino acids are specified by more than one codon.

   Redundancy or degeneracy of the genetic code signifies that a single amino acid can be encoded by multiple different codons. This is a key feature that helps to buffer against mutations.

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