Mammals contain a diploid genome consisting of at least 10⁹ bp. If this amount of DNA is present as chromatin fibers, where each group of 200 bp of DNA is combined with 9 histones into a nucleosome and each group of 6 nucleosomes is combined into a solenoid, achieving a final packing ratio of 50, determine (a) the total number of nucleosomes in all fibers, (b) the total number of histone molecules combined with DNA in the diploid genome, and (c) the combined length of all fibers.

Key Concepts

Diploid Genome

A diploid genome contains two complete sets of chromosomes, one inherited from each parent, totaling approximately 10⁹ base pairs (bp) in mammals. This genetic material is organized into structures called chromatin, which condense to form chromosomes during cell division. Understanding the diploid nature is crucial for calculating the total number of nucleosomes and histones, as it affects the overall DNA content.

Nucleosome Structure

Nucleosomes are the fundamental units of chromatin, consisting of a segment of DNA wrapped around a core of histone proteins. Each nucleosome typically contains about 200 bp of DNA and is formed by the association of DNA with nine histone proteins. This structure plays a key role in DNA packaging and regulation, making it essential for determining the total number of nucleosomes in the genome.

Chromatin Packaging

Chromatin packaging refers to the hierarchical organization of DNA into higher-order structures, such as solenoids, which further compact the DNA for efficient storage within the nucleus. In this context, six nucleosomes combine to form a solenoid, achieving a significant packing ratio. Understanding this process is vital for calculating the combined length of all chromatin fibers and the overall organization of the genome.