AP BIOLOGY

Detailed explanation-1: -Chromosomal DNA is packaged inside microscopic nuclei with the help of histones. These are positively-charged proteins that strongly adhere to negatively-charged DNA and form complexes called nucleosomes. Each nuclesome is composed of DNA wound 1.65 times around eight histone proteins.

Detailed explanation-2: -Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4. The chain of nucleosomes is then wrapped into a 30 nm spiral called a solenoid, where additional H1 histone proteins are associated with each nucleosome to maintain the chromosome structure.

Detailed explanation-3: -Chromosomes have proteins called histones that bind to DNA. DNA has two strands that twist into the shape of a spiral ladder called a helix.

Detailed explanation-4: -Electrostatic interactions and hydrogen bonds between histones and DNA are vital for the stable organization of nucleosome core particles, and for the folding of chromatin into more compact structures, which regulate gene expression via controlled access to DNA.

Detailed explanation-5: -The nucleosome is the fundamental unit of chromatin in eukaryotes (1). It contains two copies each of histone proteins H2A, H2B, H3, and H4, and 146/147 basepairs (bp) of DNA (1, 2). The DNA stably contacts the surface of the histone protein octamer core in a left-handed superhelix of almost two turns.