DNA

Question 1

What is a karyotype?

Answer 1

The organisation of all the chromosomes within a eukaryotic cell during metaphase

Question 2

Tell me about the organisation of chromosomes within the cell

Answer 2

Individual chromosomes occupy a distinct subnuclear territory, even during interphase.
Chromosomes are highly coiled fibres of chromatin where DNA is wrapped around octameric histone cores called nucleosomes.

Question 3

Tell me about interphase chromosomes

Answer 3

Comprise of a set of dynamic fractal globules- globules within globules.
Can reversibly condense and decondense without knotting to open up DNA for transcription.

Nuclear periphery of interphase contains transcriptionally inactive DNA in regions called LADs(Lamina-associated domain)

Question 4

Tell me about kinetochores

Answer 4

Kinetochores bind to 17bp alpha satellite repeats in centromeres.
The inner plate binds to alpha satellite DNA.
The outer plate binds to protein components of the mitotic spindles (microtubules).

Question 5

List some specialised chromosomal sequences

Answer 5

Centromeres
Telomeres

Question 6

What are DNA transposons?

Answer 6

They move via cut & paste mechanism - non-replicative. Requires a self-encoded transposase enzyme. Some examples are P-elements in Drosophila and Ac/Ds transposons in maize

Question 7

What are retroviral transposons?

Answer 7

Replicate via an RNA intermediate. Produce new DNA copies to integrate at new loci using a self-encoded reverse transcriptase enzyme. Some examples are Ty1-copia, Ty3-gypsy and ERV elements.

Question 8

What are non-retroviral PolyA retrotransposons?

Answer 8

They are abundant in vertebrate genomes, replicate via RNA intermediates using a self-encoded reverse transcriptase via a copy and paste mechanism. Some examples are L1 elements, Alu elements, Mouse B1 elements, LINEs and SINEs