Chapter 10 - Chromatin Flashcards
Mass Composition of Chromatin
DNA: 30%
Protein: Histones: 30%
Protein: Non-Histone: 30%
RNA: 10%
Hierarchy of DNA Organization ensures
That the DNA is packaged in the most compact state.
dsDNA -> Wrapped 6x into nucleosomes -> 10 nm fiber
Nucleosomes
Eight small proteins that organize ~200 bp of DNA into a bead-like structure
Histones
The proteins that constitute the inner core of the nucleosome around which the DNA is wrapped
• Packaging of the DNA into a nucleosome generates
a chromatin fiber that is ______ in diameter.
About 10 nm
Hierarchy of DNA Organization ensures
That the DNA is packaged in the most compact state. dsDNA -> Wrapped 6x into nucleosomes -> Wrapped 40x into 10 nm fiber -> Wrapped 1,000-10,000x into 30 nm fiber
• Packaging of the DNA into a nucleosome generates
a chromatin fiber that is ______ in diameter.
About 10 nm
30 nm fiber is
Coiled into a helical structure that includes about 6 nucleosomes per turn. 30 nm in diameter.
30 nm fiber is
Coiled into a helical structure that includes about 6 nucleosomes per turn. 30 nm in diameter.
DNA can be:
Nucleosome-bound or Linker DNA
MNase
The exposed linker DNA is the cleavage site of the micrococcal nuclease (MNase)
MNase
The exposed linker DNA is the cleavage site of the micrococcal nuclease (MNase).
Demonstrate that >95% of DNA is nucleosome bound.
Typically _______ bp DNA wraps around a nucleosome.
- Typically ~200 bp DNA wraps around a nucleosome.
* Varies from 154-260 bp between species and/or mammal tissue.
Nucleosome
Histones form a cylindrical structure:
Diameter of 11 nm
Height of 6 nm
DNA wraps 1.66 turns around the outside of the nucleosome.
DNA enters and exits within close proximity.
Sites separated by ~80 bp are also in closer proximity due
to “wrapping” of the DNA.
Core DNA
Directly interacts with the histone octamer, is resistant
to MNase digestion, and consistently 146 bp.
Linker DNA
Located between histone octamers, digested by MNase, and includes 8-114 bp.
Nucleosome
Histones form a cylindrical structure:
Diameter of 11 nm
Height of 6 nm
DNA wraps 1.66 turns around the outside of the nucleosome.
DNA enters and exits within close proximity.
Sites separated by ~80 bp are also in closer proximity due
to “wrapping” of the DNA.
Linker DNA
Located between histone octamers, digested by MNase, and includes 8-114 bp.
Each histone includes
3-α helices and 2-interconnecting loops (called the histone
fold)
Histone complex formation
- H3 and H4 form a tetramer (H32-H42)
- H2A and H2B form a dimer (H2A-H2B)
H32-H42 tetramer form
“Horseshoe” and constitutes the 11 nm diameter of the nucleosome.
H2A-H2B dimer
Bind each end of the H32-H42 tetramer “horseshoe.”
H2A-H2B dimer
Bind each end of the H32-H42 tetramer “horseshoe.”
Linker histones:
- H1
- Functions to “seal” DNA in the nucleosome with its location at the site where DNA “enter/exits”
- Functions to promote 30 nm fiber
- Can be extracted from chromatin without affecting nucleosome structure.
Core Histones include:
- Globular core
- N- and/or C- terminal tail
- N-terminal tail: H3, H4, H2A, and H2B
- C-terminal tail: H2A and H2B
The amino acid on the histone tail is subject
To covalent modification or protein post-translational
modification (PTM).
The lysine amino acid is a common site for multiple
modifications.
The amino acid on the histone tail is subject
To covalent modification or protein post-translational
modification (PTM).
The lysine amino acid is a common site for multiple
modifications.
