lec 4. chromosome structure Flashcards
chromosome painting
allows individual chromosomes to be distinguished at metaphase due to chromosomes occupying distinct subnuclear territories
chromatin
highly coiled chromosomes resembling ‘beads on a string’ which are nucleosomes
histones
proteins that package and order DNA into nucleosomes
types: H2A, H2B, H3, H4
function of histones
bind to DNA backbone due to being positively charged. Their N-terminals interact with proteins, condensing and opening DNA, which facilitates regulation, structure and function
linker histones
(eg. H1) limit DNA movement on histone octamers which is characteristic of heterochromatin
interphase chromatin
made up of ‘fractal globules’ that reversibly condense and decondense and move in and out of spaces that are transcriptionally active (internal cell region)
CENP-A
H3 variant histone that is associated with alpha-satellite DNA and binds to inner plate of kinetochore
H3-K4me
methylated H3 histone that helps to hold sister chromatids together
unique sequences
made up of protein-coding DNA (1.5%) and non-protein-coding DNA that encodes regulatory info about where and when protein-coding genes are expressed
repeated sequences
made up of simple sequence repeats, segmental duplications, and transposons
transposons
genetic elements that jump around the genome
most copies of these elements are defective
DNA transposons
cut & paste mechanism without self-duplication using transposase
Retroviral retrotransposon
replicate RNA intermediates, produce DNA copies that integrate in new positions with reverse transcriptase
Non retroviral polyA retrotransposon
replicate via RNA intermediates using own retrotransposon encoded reverse transcriptase then cuts & pastes.
can disrupt genes and cause disease like haemophilia which is caused by transposon inserting into clotting factor gene
nucleosome
a length of DNA wrapped around a histone octamer
