Eukaryotic Genomes and Chromosomes: Structure and Packaging Flashcards
Structure of Eukaryotic Chromosome
- Each chromosome is a
linear double-stranded
DNA molecule - Packaged as a complex of DNA and protein called CHROMATIN
- Telomeres play a role in chromosome integrity, ageing and disease
Euchromatin
Loosely packed chromatin, transcriptionally active
- Towards the end of chromosome
Heterochromatin
Tightly packed chromatin, transcriptionally inert
- In the middle of chromosome
Telomeres
- Play a role in chromosome integrity, aging, and disease
- Prevents the chromosome from shortening
Packaging a Eukaryotic Chromosome
- DNA duplex (2nmwraps around histone fiber - 11nm in diameter
- Wraps around to form chromatin fiber - 30 nm
- Then coiled to a 300nm coiled chromatin fiber
- Coiled coil - 700nm diameter
- Metaphase chromatids - 1400 nm
Scaffold proteins
- Coils into condensed structure usually during metaphase
Why is DNA so tightly packed?
- Easier to separate when transcribing certain sequences of DNA
Cytogenetics
The study of the structure and function of chromosomes
- Chromosomes can be visualised at specific points in the cell
cycle - Many organisms are diploid - we see two copies of each
chromosome (maternal, paternal).
DNA content changes during cell cycle
The amount of DNA in a cell is
dependent on the cell cycle
phase.
* DNA is most abundant in the
interphase before the onset of
cell division (mitosis and
meiosis)
=> Post gap2 DNA has doubled and condensed
- Less abundant as gametes
Fluorescence in situ hybridisation
Tags specific molecule with a dye that emits fluorescence
Karyotyping
Number, size, and morphology
of all the chromosomes in the genome
Metacentric
when centromere is towards middle of chromosome
Submetacentric
Centromere towards the end of chromosome
Acrocentric
Centromere is right at the end of chromosome
