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Histone

Chromatin folding

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Chromatin: The formation of chromosomes Chromatin is packed into chromosomes during mitosis. We will look at the steps from interphase to metaphase There are several levels of organisation in terms of chromatin folding? Free DNA 2nm Formation of the nucleosome: The DNA strand wraps around a core of eight histones (H2A, H2B, H3, H4: x2) 1.65 times. Also known as ?beads-on-a-string? and is the basic chromatin structure. 10nm An H1 histone tails binds on the outside of the coil on each nucleosome unit, now chromatosome units. Further condensing occurs: 30nm Interactions between: Interactions between chromatosomes (nucleosomes and H1 histones) leads to more folding of the 30nm fibres, creating a thicker fibre. 30nm

Types of chromatin

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Chromatin: Types of chromatin Chromatin In non-dividing cells, the DNA exists as chromatin and appears uncoiled and randomly dispersed After DNA replication (S phase) the chromatin begins to condense in preparation for mitosis Chromatin consists of 50% DNA, 50% proteins, mainly histones Chromatin is the structure that the eukaryotic genome is packaged into It allows long molecules of DNA to fit into the small volume of the nucleus The basic structural unit of chromatin is the nucleosome Further folding and compaction of chromatin produces visible metaphase chromosomes during cell division Heterochromatin vs Euchromatin Euchromation Active Chromatin The majority of chromatin is this form Less condensed, lightly packed in the nucleus (basic ?beads on a string? form ?check)

AP Bio Campbell 7E Chapter 19 Test Bank

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Ch 19 Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. ____ 1. The condensed chromosomes observed in mitosis include all of the following structures except a. nucleosomes. b. 30-nm fibers. c. 300-nm fibers. d. looped domain. e. ribosomes. ____ 2. Under the electron microscope, unfolded chromatin resembles "beads on a string." What do the "beads" represent? a. nucleosomes b. ribosomes c. beadosomes d. molecules of DNA polymerase e. molecules of RNA polymerase ____ 3. In a nucleosome, what is the DNA wrapped around? a. polymerase molecules b. ribosomes c. mRNA d. histones e. nucleolus protein
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