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True or False: Every chromosome has both heterochromatin and euchromatin while in interphase.
Highly condensed throughout cell cycle
Characteristic feature of centromeres, telomeres, seen at some other (often ill-defined) chromosomal locations
Typically composed of highly repetitive DNA sequences (tandem repeats)
Generally contains very few genes – exhibits little transcription
Genes translocated into heterochromatic sequence (through chromosome breakage and rejoining) are typically transcriptionally inactivated
Every female (2X) somatic cell contains one inactive X chromosome (the “Barr body”) that is heterochromatic and highly condensed
Becomes highly condensed only at metaphase
- Intermediate level of condensation
- during interphase
Represents the major portion of chromatin – contains most of the genes
BUT, genes within it can be transcriptionally active or inactive
What is the physical form of euchromatin during interphase?
In chromatin, what is the raito of dna to proteins by weight?
1 dna : 2 proteins
In chromatin, what is the ratio of non-histone proteins to histone proteins by weight?
1 : 1
In chromatin, what is the ratio of DNA to RNA by weight?
1 DNA : 0.06 RNA
Is the H1 histone as conserved as much as the other histones?
No. It has the ability to be changed without losing functionality.
What protein subunits make up the histone octomer?
Describe the structural organization of histone proteins.
3 Alpha Helix structures
Highly conserved N terminus tail ( 20-30 AA with highly positive charge.)
Describe the formation of the histone octomer.
Two H3 & H4 dimers come together. Then H2A & H2B dimers attach to the front and the back.
The process of histone octomer formation is catalyzed by _____, which are called _____.
Chromatin Assembly Factors (CAFs)
How many base pairs are part of a nucleosome?
DNA is wound around the core octamer _____ times in a _____ superhelical turn.
How are nucleosomes pulled together in the 30nm fiber?
The basic residues located on the tails of the histone subunnits attach to the acidic residues of other octomers.
Histone H1 has _____ separate DNA binding sites that allow it to tether the _____ to the _____.
the long _____ allows adjacent H1 Molecules to interact with one another, which allows nucleosomes to pack tightly into the 30nm fiber.
The average spacing of the nucleosome is _____ bp and the average linker length is _____bp.