Unit 10: Chromatin and Gene Regulation Flashcards
Nucleosome
the basic structural subunit of chromatin, containing about ~200 bp of DNA and an octamer of positively charged histone proteins
Histone tails
flexible amino- or carboxy- terminal regions of the core histones that extend beyond the surface of the nucleosome
-histone tails are sites of extensive post-translational modification
Fill in the blanks: The eukaryotic DNA is organized into ________, where the genetic material is organized in a hierarchical manner.
The eukaryotic DNA is organized into CHROMATIN, where the genetic material is organized in a hierarchical manner.
The basic structure unit of chromatin is called a ?
nucleosome
Fill in the blanks: Histones form the core of the _________, with the DNA wrapped around it lying on the surface.
Histones form the core of the NUCLEOSOME with the DNA wrapped around it lying on the surface.
10nm fiber
a linear array of nucleosomes generated by unfolding from the natural condition of chromatin
What are linker histones?
a family of histones (such as histone H1) that are not components of the nucleosome core but stabilize histone tails
-linker histones bind nucleosomes and/or linker DNA and promote 30nm fiber formation.
What is the organizational level of a nucleosome in order
1) The nucleosome
2) 10nm fiber coil to for a fiber w/30 nanometer diameter, which is a coil of chromosomes
3) this results further 40 fold compaction of the DNA - the structure of this fiber requires the histone tails and is stabilized by linker histones
4) the 30nm fiber is further compacted into interphase chromatin or miotic chromosomes
30nm fiber
a coil of nucleosomes
-it is the basic level of organization of nucleosomes in chromatin
what is a nonhistone?
are any structural proteins found in a chromosomes other than the histones.
Their functions include:
- gene expression
- gene control
- higher order structure
TRUE OR FALSE: DNA has twice as much protein as chromatin
FALSE:
the chromatin contains almost twice as much protein as DN
What is the role micrococcal nuclease (MNase)?
MNase clips/cleaves the region between nucleosomes called linker DNA.
What happens when linker DNA is cleaved?
-it releases individual nucleosomes
What do we see when chromatin is treated w/MNase and the produces are run on a gel?
-we see integral multiples of a unit length of about 200 base pairs. So fragment sizes would be 200 bp or multiples of 200.
Fill in the blank: More than ____% of DNA is recovered in nucleosomes or multimers following cleavage by MNase.
95%
what is the typical size of the DNA in a nucleosome?
about 200 basepairs but can vary between 154 and 260 basepairs. The average value may be different in different tissues in an organism or even between different parts of the genome w/in a single cell
Fill in the blanK: nucleosomal DNA is divided into two regions: the _____ DNA and the ________ DNA, depending on its susceptibility to MNase
nucleosomal DNA is divided into the CORE DNA and the LINKER DNA, depending on its susceptibility to MNase
What is the core DNA?
- part of the nucleosomal DNA that has a fixed length of 146 bp aand is found on the core particles produced by prolonged digestion w/MNase
- The core DNA reflects the minimum length of DNA needed to form a stable nucleosome and is resistant to digestion by nucleases
What is the linker DNA?
-part of the nucleosomal DNA. It is a region of 8 to 114 base pairs and is susceptible to early cleavage by nucleases.
What is the structure of a nucleosome and what are the core histone subunits of a nucleosome?
SUBUNITS (core histones): H2A H2B H3 H4
a nucleosome contains ~200 bp of DNA and two copies of each core histone forming an octamer,
What is the histone octamer structure?
the histone structure has a H3(ii) - H4(ii) tetramer associated w/two H2A-H2B dimers
TRUE OR FALSE: The nucleosome consists of approximately equal masses of DNA and histones.
TRUE
Why are histones positively charged? What does this charge help them bind to?
b/c they are rich in arginine and lysine. b/c of this they bind to DNA w/high affinity and are responsible for DNA packaging in eukaryotes.
Which histones are the most conserved proteins known?
H3 and H4