Problem 151 - Objective Biology for NEET

Question

Assertion: The distance between adjacent base pair in B- DNA is \(3.4 \mathrm{~A}^{\circ}\). Reason: One full turn of helical strand of B-DNA contain 10 bp and the length of this pitch is \(34 \mathrm{~A}^{\circ}\).

Step-by-Step Solution

Answer

The distance between adjacent base pairs in B-DNA is indeed 3.4 Angstrom, as the length of one full turn is 34 Angstrom, and one turn consists of 10 base pairs.

Step 1 - Understanding the Structure of B-DNA

B-DNA is a form of DNA with 10 base pairs per turn and a length of 34 Angstrom. One turn is also referred to as a pitch.

Step 2 - Calculating the Distance Between Adjacent Pairs

To find the distance between adjacent base pairs, it's necessary to divide the length of one full turn, which is 34 Angstrom, by the number of base pairs in one turn, which is 10. The formula is distance = length of full turn / number of base pair in one turn.

Step 3 - Substituting the Values

Replacing the values in the formula we have distance = 34 Angstrom / 10 = 3.4 Angstrom. Therefore, the distance between adjacent base pairs in B-DNA is 3.4 Angstrom.

Key Concepts

B-DNA

B-DNA is one of several distinct forms of DNA structure. The "B" notation signifies its most prevalent form in biological systems. This is the structure often illustrated in textbooks, displaying a right-handed helix with specific and consistent measurements.
B-DNA features:

• A right-handed helix
• 10 base pairs per helical turn
• A helical turn or "pitch" of approximately 34 Angstrom

The structure of B-DNA is stabilized through hydrogen bonds between complementary base pairs. It is important to note that these characteristics help in DNA's biological functions such as storing genetic information and guiding the synthesis of proteins.

Base pairs

Base pairs are the building blocks of the DNA double helix. In B-DNA, a single turn of the helix typically contains 10 base pairs. These pairs form through hydrogen bonding between nucleotide bases.
These nucleotide bases pair as follows:

• Adenine (A) with Thymine (T)
• Cytosine (C) with Guanine (G)

Each pair plays a crucial role in encoding genetic information and ensuring the accuracy of DNA replication. Understanding base pairing is essential for grasping how DNA carries genetic instructions and maintains cellular integrity.

Angstrom

An Angstrom is a unit of length equal to 0.1 nanometers, denoted by the symbol \(\text{Å}\) or \(\mathrm{A}^{\circ}\).This unit is particularly useful in molecular biology and chemistry for measuring atomic and molecular structures.
When discussing B-DNA, the term Angstrom is used to describe the spacing and periodicity of the helix:

• One helical turn measures 34 Angstrom
• The distance between adjacent base pairs is 3.4 Angstrom

Using Angstroms allows scientists to express these distances with precision, given the very small scale of molecular biology.

Helical turn

A helical turn or "pitch" refers to the length a DNA molecule completes one spiral or coil of the double helix. In the context of B-DNA, one full turn of the helix encompasses 10 base pairs and measures approximately 34 Angstrom.
The concept of helical turn is crucial for understanding the DNA structure:

• The helical turn ensures that the double helix maintains its structural integrity and consistency.
• It also affects how the DNA is packaged within cells and regulates access to the genetic code.

Overall, understanding the helical turn aids in comprehending how DNA's 3D structure supports its function in living organisms.