Chromosome Structure PART 2 Flashcards
What are the 2 areas that have specific structural importance in chromosomes?
The centromere and the telomere
What is the centromere?
Where 2 sister chromatids are held together
Sites at which the spindle attaches during cell division
Normally consists of highly repeated satellite DNA
What is the telomere?
-Located at the ends of chromosomes
-Contain multiple repeats of simple short DNA sequences
-Believed to be responsible for maintaining chromosomal integrity by protecting against DNA degradation or rearrangement
-Cellular age can be found out by length of telomere - shortens with age
How are telomeres added to the ends of chromosmes?
By an RNA-containing enzyme - telomerase
DNA must be condensed by a factor of more than…………
10*5
What are the protein stools that DNA are wrapped around called?
Nucleosomes
What are the 2 classes of chromatin proteins
-Histones (abundant)
-Nonhistone proteins
What are histones?
Small positivel charged arginine or lysine rich proteins that interact via ionic bonds with the neagtively charged phosphate groups on the polynucleotide backbone
What are the 5 distinct histones?
H1, H2A, H2B, H3, H4
What is the nucleosome?
Made up of pairs of histones (H2A, H2B, H3, H4) that aggregate to form the octameric core which is the nucleosome.
DNA helix is wound around the nucleosome.
What is the function of histone 1?
It seals the ends of the DNA turns to the nucleosome core and organises the additional 40-60bp of DNA that link consecutive nucleosomes. (like beads on a string)
How many base pairs make how many turns around the histone before the DNA moves to the next histone?
146 bp of B-DNA in a flat left-handed superhelical conformation makes 1.65 turns around the histone
What are the nucleosomes wound into?
A solenoid - having 6 nucleosomes per turn
The 30nm filament has about 1200 bp in each solenoid turn
H1 histones stabilise it
What do the solenoids then form?
Long DNA loops of variable length, each conmtaining 60,000 to 150,000 bps
What is the nucleoid?
Region in a prokaryotic cell where the DNA is
