Which property of DNA double helix led Watson and Crick to hypothesise semiconservative mode of DNA replication? Explain.
Solution and Explanation
Watson and Crick observed that the two strands of DNA are anti-parallel and complementary to each other with respect to their base sequences. This type of arrangement in DNA molecule led to the hypothesis that DNA replication is semiconservative. It means that the double stranded DNA molecule separates and then, each of the separated strand acts as a template for the synthesis of a new complementary strand. As a result, each DNA molecule would have one parental strand and a newly synthesized daughter strand.
Since only one parental strand is conserved in each daughter molecule, it is known as semi-conservative mode of replication.
Top Questions on Molecular Basis of Inheritance
Study the given below single strand of deoxyribonucleic acid depicted in the form of a “stick” diagram with 5′ – 3′ end directionality, sugars as vertical lines and bases as single letter abbreviations and answer the questions that follow.
Name the covalent bonds depicted as (a) and (b) in the form of slanting lines in the diagram.
How many purines are present in the given “stick” diagram?
Draw the chemical structure of the given polynucleotide chain of DNA.- CBSE CLASS XII - 2025
- Biology
- Molecular Basis of Inheritance
Study the given molecular structure of double-stranded polynucleotide chain of DNA and answer the questions that follow.
(a) How many phosphodiester bonds are present in the given double-stranded polynucleotide chain?
(b) How many base pairs are there in each helical turn of double helix structure of DNA? Also write the distance between a base pair in a helix.
(c) In addition to H-bonds, what confers additional stability to the helical structure of DNA?- CBSE CLASS XII - 2025
- Biology
- Molecular Basis of Inheritance
Use the given information to select the amino acid attached to the 3′ end of tRNA during the process of translation, if the coding strand of the structural gene being transcribed has the nucleotide sequence TAC.
- CBSE CLASS XII - 2025
- Biology
- Molecular Basis of Inheritance
Student to attempt either option-(A) or (B):
(A) Write the features a molecule should have to act as a genetic material. In the light of the above features, evaluate and justify the suitability of the molecule that is preferred as an ideal genetic material.
OR
(B) Differentiate between the following:- [(i)] Polygenic Inheritance and Pleiotropy
- [(ii)] Dominance, Codominance and Incomplete dominance
- CBSE CLASS XII - 2025
- Biology
- Molecular Basis of Inheritance
- Distance between two consecutive base pairs of DNA is \rule{2cm}{0.1mm}
- CBSE Compartment XII - 2025
- Biology
- Molecular Basis of Inheritance
Questions Asked in CBSE CLASS XII exam
- Briefly explain how energy is produced in stars, giving two examples of the nuclear reactions involved.
- CBSE CLASS XII - 2025
- Nuclear physics
- If \( \mathbf{a} \) and \( \mathbf{b} \) are position vectors of two points \( P \) and \( Q \) respectively, then find the position vector of a point \( R \) in \( QP \) produced such that \[ QR = \frac{3}{2} QP. \]
- From the following information, calculate ‘Return on Investment’ :
Shareholders Funds ₹ 16,00,000
10% Debentures ₹ 8,00,000
Current Liabilities ₹ 2,00,000
Current Assets ₹ 5,00,000
Non-Current Assets ₹ 21,00,000
Net profit after tax was ₹ 3,00,000 and the tax amounted to ₹ 1,00,000.- CBSE CLASS XII - 2025
- Accounting Ratios
- Give reasons:
(a) Cooking is faster in a pressure cooker than in an open pan.
(b) On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult's law is shown by the resulting solution? What change in temperature would you observe after mixing liquids X and Y?- CBSE CLASS XII - 2025
- Solutions
- The electric field at a point in a region is given by \( \vec{E} = \alpha \frac{\hat{r}}{r^3} \), where \( \alpha \) is a constant and \( r \) is the distance of the point from the origin. The magnitude of potential of the point is:
- CBSE CLASS XII - 2025
- Electrostatics
Concepts Used:
Structure of DNA and RNA
DNA Structure:
Human DNA is unique and is made up of 3 billion base pairs. However, 99% of them are the same in all humans. The sequence of these bases determines what information needs to be coded that is necessary for the organism's growth and development. During the process of transcription (when DNA is replicated), a product is formed known as RNA (Ribonucleic Acid). This RNA is responsible for translating genetic information from DNA to protein followed by reading through ribosomes.
Read More: Structure of DNA
RNA Structure:
The ribonucleic acid has all the components same to that of the DNA with only 2 main differences within it. RNA has the same nitrogen bases called the adenine, Guanine, Cytosine as that of the DNA except for the Thymine which is replaced by the uracil. Adenine and uracil are considered as the major building blocks of RNA and both of them form base-pair with the help of 2 hydrogen bonds.
RNA resembles a hairpin structure and like the nucleotides in DNA, nucleotides are formed in this ribonucleic material(RNA). Nucleosides are nothing but the phosphate groups which sometimes also helps in the production of nucleotides in the DNA.
Read More: Structure of RNA