Structure of Eukaryotic Chromosomes Flashcards
approx how much dna is in a single human cell
1.8m
how much compaction if needed to fit the dna into the nucleus
approx 180,000 times
why is dna compacted
to prevent it from damage and to regulate DNA metabolism
DNA in non dividing cells forms
chromatin
DNA during mitosis forms
chromosomes
the repeating unit of chromatin is the
nucleosome
each nucleosome comprises two molecules of each of the
four core histones
each core histone dimer has how many DNA binding surfaces
6
each core histone dimer has 6 DNA binding surfaces that organises how many DNA turns
3
the histone octamer organises how many base pairs of DNA in how many turns
145 base pairs of DNA in 1 and 3/4 helical turn of DNA
Individual nucleosomes can be prepared by limited digestion of chromatin with
micrococcal nuclease
once chromatin has been digested with micococcal nuclease how is it separated
on sucrose gradients
histones are readily solubilised from chromatin by
dilute acids, e.g. 1M (10%) HCl
Which amino acids are histones rich in
positively charged arginine and lysine
how many species of histones exist
five species, designated h1 to h4. H5 is a type of h1
which histones form various aggregates
H2a, H2b, H3 and H4
histone h1 (H5) is not present in the
nucleosome
nucleosomes are ____ conserved
highly
nucleosomes are ____ proteins
basic due to lysine and arginine
histones h3 and h4 preferentially aggregate to form
tetramers
tetramers contain how many molecules of each histone
two
histone h2a and h2b also aggregate but in
stages
how many types of interaction do histones make with dna
five
what are the two types of chromatin
heterochromatin and euchromatin
heterochromatin can be described as
highly condensed, inactive genes
euchromatin can be described as
extended structure, active genes
what is the first level of organisation
the 11nm fibril
the 11nm fibril has the appearance of a necklace and each bead is known as a
nucleosome
the short length of DNA joining any two nucleosomes is termed
linker dna
how many base pairs of DNA makes up linker DNA
50bp
the first level of organisation of DNA is how many nm thick?
11nm, it is called the 11nm fibril
what is the second level of structural organisation
the 30nm solenoid fibre
how many nucleosomes per turn are in the solenoid helix
six
which histone is required for the condensation to solenoid 30nm fibre
histone h1
the 30nm fibre is inactive in
rna synthesis (transcription)
what is the third level of structural organisation
loops, rosettes and coils
what is the fourth level of structural organisation
chromatids
chromatin is maximally condensed in
mitosis
how many micrometers long are chromatids
5 micrometers
what is the nuclear scaffold
a network of proteins that cross tie DNA loops
topoisomerase 2 and protein SC2 are major components in the
nuclear scaffold
topoisomerase 2 and protein SC2 bind to which region in the chromosomal DNA
SAR - Scaffold attachment regions
SARs are highly rich in which bases
AT rich
what do SARs participate in overall
chromosome assembly and maintenance
