Question 1

Q1: Group the following as nitrogenous bases and nucleosides: Adenine, Cytidine, Thymine, Guanosine, Uracil and Cytosine.

Accepted Answer

Based on their chemical structure, the given molecules are grouped as follows: Nitrogenous Bases: These are the fundamental purine or pyrimidine structures. - Adenine - Thymine - Uracil - Cytosine Nucleosides: These are formed when a nitrogenous base is linked to a pentose sugar. - Cytidine (Cytosin...

Question 2

Q10: 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...

Accepted Answer

The lac operon shuts down after some time because the inducer, lactose, is consumed by the enzymes produced by the operon itself. Explanation: 1.  Induction: When lactose is added to the medium, it enters the E. coli cells and acts as an inducer. It binds to the lac repressor protein, inactivating i...

Question 3

Q11: Explain (in one or two lines) the function of the followings: (a) Promoter (b) tRNA (c) Exons

Accepted Answer

(a) Promoter: A specific DNA sequence located at the 5'-end (upstream) of a structural gene that serves as the binding site for RNA polymerase, thereby initiating the process of transcription. (b) tRNA (transfer RNA): An adapter molecule that reads the genetic code on mRNA via its anticodon and carr...

Question 4

Q12: Why is the Human Genome project called a mega project?

Accepted Answer

The Human Genome Project (HGP) is called a mega project due to its immense scale, complexity, cost, and ambitious goals. Key reasons include: 1.  Massive Genome Size: The project aimed to sequence the entire human genome, which consists of approximately 3.3 billion ($3.3 	imes 10^9$) base pairs. 2....

Question 5

Q13: What is DNA fingerprinting? Mention its application.

Accepted Answer

DNA Fingerprinting: DNA fingerprinting (also known as DNA profiling) is a laboratory technique used to identify and compare individuals based on their unique DNA sequences. It involves analyzing specific, highly variable regions of DNA called repetitive DNA (such as Variable Number of Tandem Repeats...

Question 6

Q14: Briefly describe the following: (a) Transcription (b) Polymorphism (c) Translation (d) Bioinformatics

Accepted Answer

(a) Transcription: Transcription is the process of synthesising a complementary RNA molecule from a DNA template. It is the first step in gene expression. The enzyme DNA-dependent RNA polymerase binds to a promoter region on the DNA, unwinds the helix, and uses one of the DNA strands (the template s...

Question 7

Q2: If a double stranded DNA has 20 per cent of cytosine, calculate the per cent of adenine in the DNA.

Accepted Answer

The calculation is based on Erwin Chargaff's rules for double-stranded DNA. Given: - Percentage of Cytosine (C) = 20% To Find: - Percentage of Adenine (A) Principle (Chargaff's Rule): 1. The amount of Adenine (A) is equal to the amount of Thymine (T). So, A = T. 2. The amount of Guanine (G) is equal...

Question 8

Q3: If the sequence of one strand of DNA is written as follows: 5'-ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of complementary strand in 5'->...

Accepted Answer

To find the sequence of the complementary strand, we apply the base-pairing rule (A with T, and G with C) and consider the anti-parallel nature of the DNA strands. Given Strand: $$5'	ext{-ATGCATGCATGCATGCATGCATGCATGC-3'}$$  Step 1: Write the complementary sequence in the 3' to 5' direction. We pair...

Question 9

Q4: If the sequence of the coding strand in a transcription unit is written as follows: 5'-ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of mRNA...

Accepted Answer

During transcription, the RNA polymerase synthesises an mRNA strand that is complementary to the template strand. The coding strand of the DNA has the same sequence as the mRNA, except that Thymine (T) in the DNA is replaced by Uracil (U) in the mRNA. Given Coding Strand (5'→3'): $$5'	ext{-ATGCATGC...

Question 10

Q5: Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.

Accepted Answer

The property of the DNA double helix that led Watson and Crick to hypothesise the semi-conservative mode of DNA replication was complementary base pairing. Explanation: Watson and Crick observed that the two polynucleotide chains of a DNA molecule are not identical but are complementary to each othe...

Question 11

Q6: 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 nu...

Accepted Answer

Nucleic acid polymerases are enzymes that synthesise nucleic acid polymers (DNA or RNA) using an existing template. They can be classified based on the type of template they use and the type of nucleic acid they synthesise. The main types are: 1.  DNA-dependent DNA polymerase: This type of enzyme us...

Question 12

Q7: How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?

Accepted Answer

Alfred Hershey and Martha Chase differentiated between DNA and protein by using radioactive isotopes to specifically label each molecule. Their experiment exploited the unique chemical composition of DNA and proteins. Basis of Differentiation: 1.  DNA contains phosphorus (P) in its sugar-phosphate b...

Question 13

Q8: Differentiate between the followings: (a) Repetitive DNA and Satellite DNA (b) mRNA and tRNA (c) Template strand and Coding strand

Accepted Answer

Question 14

Q9: List two essential roles of ribosome during translation.

Accepted Answer

The ribosome is the cellular machinery responsible for protein synthesis (translation). Its two essential roles are: 1.  Providing a Platform for Translation: The ribosome provides a structural framework and binding sites for both mRNA and the charged tRNA molecules. It holds the mRNA template in th...

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