18 - Chromosome structure Flashcards
At what phase of mitosis can chromosomes be easily distinguished?
During Metaphase
What is the organised representation of all the chromosomes in metaphase known as?
The Karyotype.
What is a chromosome?
A highly coiled fibre of chromatin, with nucleotides along the surface.
What does the biochemical analysis of nucleosomes reveal?
A protein core in which the DNA is wrapped around, the protein subunits of the nucleotide are known as core histones.
What do the N-terminal tails of the 8 core histones do?
They project out of the nucleosome and are free to interact with other proteins, they facilitate the regulation of chromatin structure and function.
What is the function of Linker Histones?
- They strap the DNA onto histones octamers and limit movement of DNA relative to the histone octamer.
- They also stabilise the formation of the 30nm fibre and facilitates the establishment of transcriptionally silent heterochromatin.
How is the DNA packaged?
By histone octamers into compact 30nm chromatin scaffolds.
What is chromatin engineered to do?
To permit flexible responses to altered transcription factor activity caused by changes in cell differentiation status and signalling pathway activities.
What does interphase chromatin do?
It comprises a set of dynamic fractal globules (globules within globules) that can reversibly condensed and decondense without becoming knotted.
What is the nuclear periphery in interphase cells composed of?
Transcriptionally inactive DNA, The RNA transcripts are usually in the centre and excluded from the periphery.
What do chromosomes contain?
Specialised DNA sequences that facilitate reliable and complete DNA replication and segregation of duplicated chromosomes during cell division.
What are centromeres?
They are structures connected to the mitotic spindle in mitosis, they are the areas in which the 2 sister chromatids join. They are also connected to the kinetochore.
What are telomeres?
- They are specialised repetitive DNA sequences at the end of the chromosome.
- They exist as single stranded TTAGGG repeats synthesised by the telomerase enzyme
What is the importance of telomeres?
They define chromosome ends and maintain chromosome integrity.
What does chromosome segregation during cell division require?
The attachment of chromosomes to the mitotic or meiotic spindle
What does the alpha-satellite DNA in centromeres do?
They readily form condensed chromatin with histone octamers containing unusual subunits
What is the purpose of the kinetochore inner plate?
It binds to chromatin containing the alpha satellite DNA.
What is the purpose of the kinetochore outer plate?
It binds to the protein components of the mitotic spindle, eg microtubules.
What is the kinetochore in yeast?
A basket that links a single nucleosome of centromeric chromatin to a single microtubule.
What is increased biological complexity of organisms accompanied by?
More genes including an increasing amount of non-protein coding DNA for regulating transcription and organising access to protein coding genes.
What are the 3 different types of repeated DNA that makes up almost half of the human genome?
DNA transposons, Retroviral transposons, Non-retroviral polyA transposons.
What are transposons?
Mobile genetic elements that jump around the genome also called transposable elements.
What do transposons do?
They encode transposase which allow them to move around by a cut and paste mechanism
How do retroviral transposons function?
- They act like retroviruses and use reverse transcriptase to integrate at new genomic locations.
- they use self encoded reverse transcriptase
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