Q.1) Group the following as nitrogenous bases and nucleosides:
Adenine, Cytidine, Thymine, Guanosine, Uracil and Cytosine
Ans:
Nitrogenous Bases: Adenine, Cytosine, Thymine, Uracil
Nucleosides: Cytidine, Guanosine
Explanation: A nucleoside is formed when a nitrogenous base is linked to a pentose sugar through an N-glycosidic bond.
Q.2) If a double-stranded DNA has 20% cytosine, calculate the percentage of adenine.
Ans: Percentage of adenine = 30%
Explanation: In DNA, G pairs with C and A pairs with T. If cytosine is 20%, guanine is also 20%. The remaining 60% is shared equally by adenine and thymine.
Q.3) Given the DNA strand:
5’-ATGCATGCATGCATGCATGCATGCATGC-3’
Write the complementary strand in 5’→3’ direction.
Ans:
5’-GCATGCATGCATGCATGCATGCATGCAT-3’
Q.4) If the coding strand of DNA is:
5’-ATGCATGCATGCATGCATGCATGCATGC-3’
Write the mRNA sequence.
Ans:
5’-AUGCAUGCAUGCAUGCAUGCAUGCAUGC-3’
Q.5) Which property of DNA led Watson and Crick to propose semi-conservative replication?
Ans: Complementary base pairing of DNA (A with T and G with C) suggested that each strand can act as a template during replication, resulting in one parental and one newly synthesised strand.
Q.6) How did Hershey and Chase prove that DNA is the genetic material?
Ans: They used radioactive phosphorus (³²P) to label DNA and radioactive sulphur (³⁵S) to label protein in bacteriophages. Only radioactive DNA entered bacterial cells, proving that DNA is the genetic material.
Q.7) Differentiate between:
(a) Repetitive DNA and Satellite DNA
Ans: Repetitive DNA contains sequences repeated many times and may code for proteins, whereas satellite DNA is non-coding, tandemly repeated DNA found near centromeres.
(b) mRNA and tRNA
Ans: mRNA carries genetic information from DNA to ribosomes, while tRNA transports amino acids to ribosomes during protein synthesis.
(c) Template strand and Coding strand
Ans: Template strand has 3’→5’ polarity and is used for transcription, whereas the coding strand has 5’→3’ polarity and matches mRNA sequence except for thymine.
Q.8) List two roles of ribosome during translation.
Ans:
- Provides binding sites for tRNA carrying amino acids.
- Catalyses peptide bond formation between amino acids.
Q.9) Why does lac operon shut down after some time even in presence of lactose?
Ans: Due to catabolite repression. When glucose levels rise, cAMP levels fall, CAP-cAMP complex does not form and transcription of lac operon stops.
Q.10) Why is Human Genome Project called a mega project?
Ans: It involved sequencing 3 billion base pairs, huge cost, massive data storage, advanced computational tools and global collaboration over 13 years.
Q.11) What is DNA fingerprinting? Mention its applications.
Ans: DNA fingerprinting identifies individuals based on variations in repetitive DNA sequences (VNTRs).
- Paternity testing
- Forensic investigations
- Population and evolutionary studies
Q.12) List types of nucleic acid polymerases.
Ans:
- DNA-dependent DNA polymerase (Replication)
- DNA-dependent RNA polymerase (Transcription)
Q.13) Explain the function of:
(a) Promoter: Site for binding of RNA polymerase to initiate transcription.
(b) tRNA: Brings amino acids to ribosomes during translation.
(c) Exons: Coding regions of genes expressed in mature mRNA.
Q.14) Briefly describe:
(a) Transcription: Synthesis of RNA from DNA template.
(b) Polymorphism: Genetic variation at a specific DNA site in a population.
(c) Translation: Synthesis of proteins using mRNA template.
(d) Bioinformatics: Use of computers to store and analyse biological data.