Lecture 15 - Chromosome structure and genome organization - part 1 Flashcards
Each base pair of B-DNA contributes about _______Angstroms to its length
3.4
The 23 chromosomes of the 3 billion bp human genome have a length of about
1 meter
Each chromosome is a complex of
linear duplex DNA and protein
Chromosomes assume their most condensed forms only during
metaphase, the stage of the cell cycle when the chromosomes align on the mitotic spindle
Chromatin
A cells DNA with all associated proteins
Eukaryotic DNA is tightly bound to
histones
What constitutes half the mass of a eukaryotic chromosome?
histones
Chromatin serves to
compact and organize eukaryotic DNA
Chromatin greatly influences
gene regulation
Chromatin is made up of repeating units called
nucleosomes
What four histone proteins are associated with DNA
H2A, H2B, H3, and H4
H1 is associated with
the nucleosome
Histones have strong _______ properties
basic
In histones, 25% of the amino acids are either
arginine or lysine
Histones have positively charged amino acids that can
interact strongly with negatively charged DNA which stabilizes the core nucleosome
Histone (H1) further stabilizes the complex by binding to the
linker DNA
Histones bind exclusively to
the inner face of DNA
Micrococcal nuclease degrades
chromatin to single nucleosomes
The DNA superhelix has a radius of
42 Angstroms
The DNA superhelix has a pitch (rises per turn) of
26 Angstroms
Does DNA follow a uniform superhelical path?
No
The left-handed wrapping of DNA around the histone octamer stores
negative supercoils
If the DNA in a nucleosome is straightened out, the DNA will be
underwound
Underwinding is what is needed to
separate the two DNA strands during replication and transcription
30 nm Chromatin fiber has how many nucelosomes?
12
In 30 nm Chromatin, the nucleosomes follow a zigzag path such that
all odd-numbered nucleosomes form a stack as do all even-numbered nucleosomes
1 Angstrom is about ______ nm?
10
30 nm Chromatin fiber has two stacks of nucleosomes winding around each other in
two left-handed helices
30 nm Chromatin fiber has how many nucleosomes per turn?
28
DNA in assembly with chromatin fiber is compacted by approximately _____ fold
36
Naturally occurring chromatin has more
irregularly spaced nucleosomes
The 30 nm fiber in chromatin is stabilized by interactions involving
H2A-H2B dimers and histone H4
H4’s positively charged N-terminal tail can bind to a negatively charged region on an exposed face of the
H2A-H2B dimer in a neighboring nucleosome
Acetylation of H4’s N-terminal tail reduces its
positive charge
Each histone has a ______ tail that extends out from the core structure
amino-terminal
Histone tails contain a number of _________ residues
lysine and arginine
Covalent modifications of the histone tails play an important role in
regulating gene expression via chromatin modeling
HAT stands for
Histone acetyltransferase
HAD stands for
Histone deacetylase
Chromatin structure plays a major role in controlling
eukaryotic gene expression
In eukaryotic gene expression, highly compact chromatin contains genes that are
turned off
In eukaryotic gene expression, less compact chromatin contains genes that are
turned on
Euchromatin
Loosely packed chromatin
Heterochromatin
Densely packed chromatin
In chromatin loops, loops of DNA are attached to a
protein scaffold
In chromatin loops, the loops enter and exit the scaffold at
nearly the same point
Matrix-attachment regions (MARs), also known as Scaffold-attachment regions (SARs) are
DNA sequences interspersed in the genome
MARs anchor to the nuclear matrix, forming
radial loops
In chromatin loops, each loop forms a closed circle by the attachment of its base to
the protein scaffold and thereby maintains its negative supercoiling
Nonhistone proteins constitute about ______ % of chromosomal proteins
10
Nonhistone proteins participate in
organizing the DNA in higher-order structure
