Chapter 8 - Genome structure, Chromosome, and the Nucleosome Flashcards
Describe bacterial chromosomes.
Found in the cytosol, often circular and called nucleoid.
What is the difference between heterochromatin and euchromatin.
Heterochromatin: the condensed form of chromatin. Abundant heterochromatin is seen in resting cells. About 10 % of the genome. Mostly inactive, centromere and telomere. Large tandem arrays of short repeated sequence that do not code for proteins.
Euchromatin: is threadlike and delicate. It is most abundant in active, transcribing cells. 80-90 % of the genome. Ususallt 30-nm fibre and looped domains. Less dynamic.
What is the task of centromers?
it attaches the daughters DNAs to the mitotic spindle via kinetochore and allow proper segregation int eh M-phase.
What is a lamp brush chromosome?
Special form of chromosome found in oocytes that organise in large chromatin loops.
How are chromosome distinguished from each other?
By banding patterns, obtained by staining chromosomes by Giemsa stain.
Dark stained bands –> G-bands contain DNA with low GC-content, lower density of genes.
Lightly stained bands –> R-bands contain DNA with high-GC content, contain housekeeping genes as well as involved in gene-expression.
How is DNA organised into chromosomes?
DNA is wrapped around 8 histones to form a 10 nm filament. these 8 histones are separated by spacer regions of 4 nm DNA filament and H1. These units are called nucleosomes. They form the 10 nm nucleoprotein fibrils. These nucleosome are separated by the DNA spacer. The next level of coiling produces the 30 nm nucleoprotein fibres. Further looping of these fibres around a protein scaffold form the individual me phase chromosomes.
What is the function of condensins?
They are a group of proteins, which utilise energy from ATP hydrolysis and packages long DNA into chromosomes. SMC is a part of condensing, forms a tweezer like dimer that binds directly on chromatin.
Name the 5 histones.
H1, H2A, H2B, H3, H4.
What is the histone-fold domain? How is the histone core build up?
Mediates the assembly of histone-only intermediates. It is composed of 3 alpha helical regions separated by two short unstructured loops. This domain mediates the formation of head-to-tail heterodimers of specific pairs of histones. H3 and H4 form dimer and then together form a tetradimer. H2A and H2B only form heterodimers.
