LSCI 204 Lecture Notes - Lecture 13: Cytosine, Chromatin, Chromosome
8 Feb 2018
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Chapter 8: dna: the chemical nature of the gene. Chromatin has a highly complex structure with several levels of organization. The simplest level is the double-stranded helical structure of dna. At a more-complex level, the dna molecule is associated with proteins and is highly folded to produce a chromosome. The nucleosome is the fundamental repeating unit of chromatin. The space-filling model shows that the nucleosome core particle consists of two copies each of h2a, h2b, h3, and h4, around which dna coils. Chromosomal puffs are regions of relaxed chromatin where active transcription is taking place. In eukaryotic dna, cytosine bases are often methylated to form 5-methylcytosine. For example, the agouti locus helps determine coat color in mice. Parents that have identical dna sequences at this locus but have different degrees of methylation on their dna may give rise to offspring that have different coat colors. Centromeres consist of particular sequences repeated many times.
