Lecture 20 - Chromosome Structure Flashcards
What is the karyotype of the parent organism ?
Where the organised representation of all the chromosomes in a eukaryotic cell at metaphase, the chromosomes are lined in in their pair from 1-22 to XY at the end.
How many copies of a chromosome does a diploid eukaryotic cell contain ?
2 copies
What do individual chromosomes occupy ?
Distinct subnuclear territories even in interphase nuclei.
What is a chromosome?
A higly coiled fibre iof chromatin.
What does interphase chromatin look like in an electron microscope?
Resembles ‘beads on a string’, The beads are nucleosomes
What is the structure of 30nm chromatin fibre ?
A supercoiled array of nucleosomes
What is the core of nucleosomes ?
a protein core around which DNA is wound, like cotton on a bobbin
The protein subunits of the nucleosome are core histones
What is the protein core of a nucleosome’s structure like?
How does it help the regulation of chromatin structure and function ?
The N-terminal tails of the 8 core histone subunits project out from
the nucleosome core and are free to interact with other proteins,
facilitating regulation of chromatin structure and function
What do linker histones do ?
Linker histones such as H1 strap DNA onto histone octamers
and limit movement of DNA relative to the histone octamer
- this facilitates the establishment of transcriptionally silent heterochromatin
How is DNA packaged by histone octamers ?
into a compact, flexible 30nm chromatin scaffold that can be remodelled to accommodate protein complexes involved in gene transcription and DNA replication
What is chromatin engineered to do ?
Chromatin is engineered to permit flexible responses to altered
transcription factor activity caused by changes in cell
differentiation status and changes in signalling pathway activities
What does interphase chromatin comprise of?
comprises a set of dynamic, “fractal globules”
(globules within globules) that can reversibly condense and decondense without becoming knotted
How are globules organised in order to benefit chromatin?
It is like a russian doll sorta thing.
At the nucleus level there are distinct patterns of chromatin
At a higher resolution we can see areas of open and closed regions forming these patterns
within those closed regions there are distinct patterns of chromatin and those are the fractal globules.
How does the globule organisation benefit chromatin?
It is fundamental to stabilisng the regions of inactive chromatin but also allows flexibility so that cells can react to certain cues such as progenitor cells differentiating into specialised cells.
What is found inside the nuclear periphery in interphase cells ?
Composed of transcriptionally inactive DNA (red)
RNA transcripts (green) are excluded from the periphery
