Chromosomes and Chromatin Flashcards
Network of fibres found throughout inside of cell nucleus
Nuclear matrix
DNA attached to the nuclear matrix at __________
Matrix attachment regions (MARS)
Chromosomal banding pattern
G-bands
In g-bands, ______ are lower in GC content than ______
Bands, interbands
DNA of metaphase chromatin is ___________
Negatively supercoiled
During interphase, general mass of chromatin is in the form of _________
Euchromatin
Aggregate of heterochromatin from different chromsosomes
Chromocenter
_____ cleaves linked DNA and releases individual nucleosomes from chromatin
MNase
Nucleosomal DNA divided into _____ and _____ DNA depending on susceptibility to MNase
Core, linker
Nucleosome contains ______ and ________
200 bp of DNA, two copies of each of core histones (H2A, H2B, H3, H4)
Histone octamer structure
H3-H4 tetramer associated with two H2A and H2B dimers
All core histones have the structural motif of ________
Histone fold
Histone code hypothesis
Combinations of specific histone modifications define function of local regions of chromatin
Bromodomain function
Used to recognize acetylated sites on histones
Protein motifs that recognize methyl lysines
Chromodomains, PHD domains, Tudor domains
Primary structure of chromatin
10-nm fiber string of nucleosomes
Secondary structure of chromatin
Interactions between neighboring nucleosomes that promote formation of more condensed fibers, 30-nm fibers folded into higher-order 3D structures
Replication of chromatin requires assembly of ________
Nucleosomes
Common cause of nucleosome positioning
When proteins binding to DNA establish a boundary
Translational positioning
Location of histone octamer at successive turns of double helix, determines sequences in linker regions
Rotational positioning
Location of histone octamer relative to turns of the double helix, determines which face of DNA is exposed on nucleosome surface
Histone octamers disassembled ahead of ________ to remove nucleosomes
Transcription
Where are hypersensitive sites found?
Promoters of expressed genes
Locus control regions (LCR)
Regulate gene clusters
Where are LCR found?
5’ end of a chromosomal domain, consist of multiple DNase hypersensitive sites
LCRs control transcription of target genes by ____________, forming looped structures
Direct interactions
TADs
Topologically associated domains
How are mammalian chromosomes organized?
As strings of TADs about 1 Mb in size
Boundary regions between TADs contain _______
Insulator elements
Specialized chromatin structure that contain hypersensitive sites
Insulators
Insulators are able to ______ passage of effects from enhancers, silencers, and other control elements
Block
Constricted region of chromosome that includes site of attachment to the mitotic or meiotic spindle
Centromere
Fragment of chromosome that lacks centromere and is lost at cell division
Acentric fragment
Microtubule organizing center (MTOC)
Region from which microtubules emanate, in animal cells the centrosome
Eukaryotic chromosome held on the ________ by the attachment of microtubules to the ___________
Mitotic spindle, kinetochore
Centromeres characterized by…
Centromere-specific histone H3 variant and often have heterochromatin rich in in satellite DNA sequences
Function of ever-present repetitive centromeric DNA?
Unknown
Telomere required for ________
Stability of the chromosome end
Telomere consists of __________
Simple repeating structure with a G-T rich strand that extends beyond A-C strand
This enzyme base pairs between RNA template and the protruding single-stranded DNA primer to add tandem repeats to 3’ end at each chromosomal terminus
Telomerase
Telomerase expressed in _________
Actively dividing cells
Loss of telomerase results in _________
Senescence
Prevent crossing over between telomeres
Mismatch-repair system
