Ch35 - DNA Organization, Replication, And Repair Flashcards
Most abundant chromatin proteins
Histones
Consists of very long double stranded (dsDNA) molecules, histones, nonhistone proteins, and RNA
Chromatin
Characteristic of the 2/3 of histone molecules
Hydrophobic
Composed of DNA wound around an octameric complex of histone molecules
Nucleosome
4 major types of histones
H2A, H2B, H3, and H4
They form a tertamer containing 2 molecules of each
H3 and H4
145 bp of DNA and 1.75 superhelical turns
Octamer
Rhe core histones are subject to 6 types of covalentmodification or posttranslational modifications
Acetylation, methylation, phosphorylaton, ADP-ribosylaton, monoubiquitylation, and sumoylation
Acetylation of histones H3 and H4
Activation or inactivation of gene transcription
Acetylation of core histones
Chromosomal assembly during DNA replication
Involved in DNA replication and repair, and the proteins involved in RNA synthesis, processing, and transport to the cytoplasm
Nonhistone proteins
Phosphorylation of histone H1
Condensation of chromosomes
Sumoylation
Transcription repression
Amino terminal thirds of histones
Amino acids
Can confer nucleosome-like properties on DNA and thus has a central in the formation of the nucleosome
H3-H4 tetramer
ADP-ribosylation of histones
DNA repair
Condenses DNA
Histones
Stabilizes the primary particle and binds firmly two additional half-turns of DNA
H2A - H2B dimers
Group of proteins that exhibit high affinity fot binding histones
Histone chaperones
Methylation of histones
Activation and repression of gene transcription
Physical flexibility of particular nucleotide sequences to accommodate the regions of kinking within the supercoil
Phasing
2 higher order structures that provide compaction of chromatins
10nm fivtil and 30nm chromatin fiber
Consists of nucleosome arranged with their edges separated by a small distance with their flat faces parallel to the fibril axis
10nm fibril
This is formed when 10nm fibril is supercoiled with six or seven nucleosomes per turn
30nm fibril
Stabilizes the 30nm fiber
H1 histones
DNA in active chromatin contains large regions that are more sensitive to digestion by a nuclease such as…
DNase I
Shirter stretsches if 100-300 nucleotides that exhibit an even greater sensitivity to DNase I
Hypersensitive sites
Often located immediately upstream from the active gene and are the location of uninterrupted nucleosome structure caused by binding of nonhistone proteins
Hypersensitive sites
Densely packed during interphase
Inactive chromatin
Inactive chromatin
Heterochromatin
Active chromatin
Euchromatin
Type of heterochromatin that is always condensed and thus inactive
Constitutive heterochromatin
Type of heterochromatin that is at times dense, and other times actively transcribed
Facultative heterochromatin
In insects, chromosomes that have been replicated for multiple cycles wothout separation of daughter chromatids
Polytene chromosomes
Adenine-thymine-rich region containing repeated DNA sequences that range in size
Centromere