Molecular Basis of Inheritance

Key Topics

• DNA Structure: DNA is the genetic material in most organisms.
• RNA Functions: RNA serves as a messenger and has roles as an adapter, structural, and catalytic molecule.
• Central Dogma: Genetic information flows from DNA to RNA to Protein.

Exercises Summary

• Nitrogenous Bases and Nucleosides: Group adenine, cytidine, thymine, guanosine, uracil, and cytosine.
• DNA Composition: Calculate adenine percentage if cytosine is 20%.
• Complementary DNA Strand: Write the complementary strand for a given DNA sequence.
• mRNA Sequence: Derive mRNA from a coding DNA strand.
• DNA Replication Hypothesis: Discuss the property of DNA that led to the semi-conservative replication hypothesis.
• Nucleic Acid Polymerases: List types based on template nature.
• Hershey-Chase Experiment: Explain how DNA was differentiated from protein.
• DNA Types: Differentiate between repetitive DNA and satellite DNA, mRNA and tRNA, template strand and coding strand.
• Ribosome Roles: List essential roles during translation.
• Lac Operon Regulation: Explain why the lac operon shuts down after lactose addition.
• Function Descriptions: Briefly describe the functions of promoter, tRNA, and exons.
• Human Genome Project: Discuss its significance as a mega project.
• DNA Fingerprinting: Define and mention its applications.
• Processes: Briefly describe transcription, polymorphism, translation, and bioinformatics.

Molecular Basis of Inheritance

Exercises

1. Group the following as nitrogenous bases and nucleosides:
   • Nitrogenous Bases: Adenine, Thymine, Guanine, Cytosine, Uracil
   • Nucleosides: Cytidine, Guanosine
2. If a double stranded DNA has 20 percent of cytosine, calculate the percent of adenine in the DNA.
3. If the sequence of one strand of DNA is written as follows:
   • 5'-ATGCATGCATGCATGCATGCATGCATGC-3'
   • Write down the sequence of complementary strand in 5'-3' direction.
4. If the sequence of the coding strand in a transcription unit is written as follows:
   • 5'-ATGCATGCATGCATGCATGCATGCATGC-3'
   • Write down the sequence of mRNA.
5. Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.
6. Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesised from it (DNA or RNA), list the types of nucleic acid polymerases.
7. How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?
8. Differentiate between the following:
   • (a) Repetitive DNA and Satellite DNA
   • (b) mRNA and tRNA
   • (c) Template strand and Coding strand
9. List two essential roles of ribosome during translation.
10. In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?
11. Explain (in one or two lines) the function of the following:
    • (a) Promoter
    • (b) tRNA
    • (c) Exons
12. Why is the Human Genome project called a mega project?
13. What is DNA fingerprinting? Mention its application.
14. Briefly describe the following:
    • (a) Transcription
    • (b) Polymorphism
    • (c) Translation
    • (d) Bioinformatics

Common Mistakes and Exam Tips

Common Pitfalls

• Misunderstanding DNA and RNA Functions: Students often confuse the roles of DNA and RNA. Remember, DNA is primarily the genetic material, while RNA serves various roles including messenger functions.
• Confusing Nucleotides and Nucleosides: Be clear on the difference; nucleotides are the building blocks of nucleic acids, while nucleosides consist of a nitrogenous base and a sugar.
• Errors in Base Pairing: Ensure you remember the correct base pairing rules (A-T and G-C for DNA).
• Neglecting the Importance of Mutations: Many overlook how mutations can affect protein synthesis and lead to diseases like sickle cell anemia.

Exam Tips

• Practice Complementary Strand Writing: Regularly practice writing complementary DNA strands to avoid mistakes in directionality (5'-3' vs 3'-5').
• Understand the Central Dogma: Be clear on the flow of genetic information: DNA -> RNA -> Protein. This is fundamental and often tested.
• Familiarize with Genetic Code: Know how to translate mRNA sequences into amino acids, as this is a common question type.
• Review DNA Fingerprinting Techniques: Understand the significance of repetitive DNA and how it is used in forensic science.
• Clarify the Role of Ribosomes: Remember the essential functions of ribosomes during translation to avoid vague answers.