Molecular Basis Of Inheritance

Step 1: Understanding the given DNA sequence The given sequence of one strand of DNA is: ###

Step 2: Writing the complementary bases Now, we need to find the complementary bases for each nucleotide in the sequence. Applying the base pairing rules, we get: ###

Step 3: Complementary sequence in the 3' to 5' direction Starting from the left end (5') of the given strand, the complementary sequence will be formed as follows: - 5'-A \underline{T}-3'
- 5'-T \underline{A}-3'
- 5'-G \underline{C}-3'
- 5'-C \underline{G}-3'
- 5'-A \underline{T}-3'
- 5'-T \underline{A}-3'
- 5'-G \underline{C}-3'
- 5'-C \underline{G}-3'
- 5'-A \underline{T}-3'
- 5'-T \underline{A}-3'
- 5'-G \underline{C}-3'
- 5'-C \underline{G}-3'
Thus, the complementary sequence in the 3' 5' direction will be: ###

Step 4: Final answer The sequence of nitrogenous bases in the complementary strand in the 3' 5' direction is:

Step 1: Enzyme action. The enzymes responsible for breaking or cutting DNA are called **restriction endonucleases**.

Step 2: Mechanism. - Restriction endonucleases recognize specific sequences of DNA and cut at those sites. - Another enzyme, **DNase (deoxyribonuclease)**, can also non-specifically break down DNA into fragments.

Step 3: Correct enzyme. When asked generally, the correct answer is DNase.

Final Answer:

Step 1: Definition.
The semiconservative method of DNA replication was proposed by Watson and Crick and experimentally proved by Meselson and Stahl (1958). According to this model, during replication each DNA molecule produces two daughter DNA molecules, each having: Thus, half (semi) of the parental DNA is conserved in each daughter molecule.

Step 2: Process of replication. \begin{enumerate} \item Initiation: The double helix unwinds at the origin with the help of helicase enzyme. Hydrogen bonds between bases break, forming replication forks. \item Elongation: Each parental strand acts as a template. DNA polymerase adds complementary nucleotides (A with T, G with C). \item Termination: Okazaki fragments are joined by DNA ligase, resulting in two identical DNA molecules. \end{enumerate}

Step 4: Proof by Meselson and Stahl.
They used \textsuperscript{15}N heavy isotope in E. coli DNA and showed that after one generation, the DNA molecules had one parental (old) strand and one new strand, confirming the semiconservative nature.

Step 1: Understanding the Process of Protein Synthesis.
The process of protein synthesis involves two key stages: transcription and translation. Transcription is the process where mRNA is synthesized from DNA, while translation is the process where the mRNA is used to synthesize proteins.

Step 2: Analysis of options.
- (A) Translation: Translation is the process by which proteins are synthesized with the help of m-RNA. This is the correct process.
- (B) Transcription: Transcription is the process of creating m-RNA from a DNA template, not protein synthesis.
- (C) Reverse transcription: This refers to the process where RNA is reverse-transcribed into DNA, which occurs in some viruses, not in regular protein synthesis.
- (D) Replication: Replication is the process of copying DNA, not related to protein synthesis.

Step 3: Conclusion.
The process of protein synthesis with the help of m-RNA is called Translation, making option (A) the correct answer.

Step 1: Background.
The lac operon in E. coli regulates lactose metabolism. It has structural genes (Z, Y, A) controlled by a promoter, operator, and regulator gene.

Step 2: Role of Z and Y genes. \item Y gene: Codes for Permease enzyme. \end{itemize}

Step 3: Conclusion.
Thus, in the lac operon, Z and Y genes play key roles in lactose utilization: Z (breakdown) and Y (transport).

Step 1: Understanding sickle cell anemia.
Sickle cell anemia is a genetic disorder caused by a mutation in the gene coding for the beta chain of hemoglobin. This leads to defective hemoglobin known as HbS.

Step 2: Mutation involved.
In sickle cell anemia, at the sixth position of the beta-globin chain, the amino acid Glutamic Acid (hydrophilic) is replaced by Valine (hydrophobic). This substitution changes the structure of hemoglobin molecules.

Step 3: Effect of substitution.
Due to this substitution, hemoglobin molecules polymerize under low oxygen conditions, causing red blood cells to assume a sickle shape. This leads to anemia and other complications.

Step 4: Conclusion.
The correct answer is (C) Valine, as Glutamic Acid is replaced by Valine in sickle cell anemia.

Step 1: Definition.
The genetic code is the set of rules by which the sequence of nucleotides in DNA or mRNA is translated into the sequence of amino acids in proteins. Codons (triplets of nucleotides) specify particular amino acids.

Step 2: Properties of the genetic code.
\begin{enumerate} \item Triplet code: Each codon has 3 nucleotides. \item Unambiguous: One codon codes for only one amino acid. \item Degenerate: A single amino acid may be coded by more than one codon (e.g., leucine). \item Universal: Same code is used by nearly all organisms (exceptions in mitochondria). \item Comma-less: Codons are read continuously without gaps. \item Start codon: AUG (codes for methionine) initiates translation. \item Stop codons: UAA, UAG, UGA terminate translation. \end{enumerate}

Step 3: Importance.

Step 4: Conclusion.
The genetic code is a precise, universal language of life that ensures transfer of information from DNA to proteins, sustaining all forms of life.

Step 1: Sugar in RNA.
In RNA (Ribonucleic Acid), the sugar is called ribose. Ribose is a pentose sugar with the following structural feature: This hydroxyl group makes RNA chemically more reactive and less stable under alkaline conditions. As a result, RNA molecules are usually single-stranded and perform temporary roles in cells such as protein synthesis (mRNA, tRNA, rRNA).

Step 2: Sugar in DNA.
In DNA (Deoxyribonucleic Acid), the sugar is called deoxyribose. The difference is: This small change makes DNA chemically more stable, less reactive, and well-suited for long-term storage of genetic information.

Step 3: Functional Implications.

Step 4: Summary of Difference.