DNA is a polymer of nucleotides - AQA - GCSE Biology - Question 4 - 2020 - Paper 1

A nucleotide consists of three main components:

1. Phosphate Group: It is attached to the sugar molecule.
2. Sugar: In the case of DNA, this is deoxyribose, a pentose sugar.
3. Nitrogenous Base: There are four possible bases—Adenine (A), Cytosine (C), Guanine (G), and Thymine (T). Each nucleotide has one of these bases attached to the sugar.

To find the total length of the DNA double helix in a human body cell, we need to:

1. Calculate the number of pairs of nucleotides in the body cell:

   ext{Total Number of Nucleotides} = 1.2 imes 10^{10}

   ext{Number of Pairs} = rac{1.2 imes 10^{10}}{2} = 6.0 imes 10^{9}

2. Then, calculate the total length, given that each pair contributes 0.34 nm:

   ext{Total Length} = 6.0 imes 10^{9} ext{ pairs} imes 0.34 ext{ nm/pair} = 2.04 imes 10^{9} ext{ nm}

3. Convert nm to meters:

   ext{Total Length in meters} = 2.04 imes 10^{9} ext{ nm} imes 1 imes 10^{-9} ext{ m/nm} = 2.04 ext{ m}.

Non-coding parts of DNA can influence gene expression by acting as regulatory elements. They can switch genes on or off, which means they can control when and how much of a protein is produced. This regulation is crucial for various cellular functions and responses to environmental changes.