section 1 Flashcards
Chromosomes and chromatin
Histones
Small basic proteins containing high proportion of basic amino acids. (Arginine & Lysine) that package DNA in an ordely way in the cell nucleus. H1, H2A, H2B, H3, H4. C
Chromatin
Eukaryotic DNA complexed with proteins such as histones and others nonhistones involved in DNA replication and gene expression. Has 2x more protein than DNA. 10nm
Arginine and Lysine in histones
Amino acids in Histones that facilitate the binding to the negatively charged DNA molecule
Nucleosome
Basic strucutral unit of chromatin. Repeating 200bp units found by Kornberg with partial digestion of chromatin by Micrococcal nuclease. Gives chormatin beaded appearance. Shortens DNA length 6fold
Micrococcal nuclease
An enzyme that degrades DNA used to digest chromatin and find nucleosomes. Yields fragments of DNA 200bp long. Yields a continuous smear of randomly sized fragments in naked DNA.
Nucleosome core particles
when more extensive digestion of chromatin with Mn is done. Contain 147bp of DNA wrapped 1.67 turns around histone core that has 2 molecules each of H2A,H2B,H3,H4
Core histones
The histones in Nucleosome core particles, w/ 2 of each H2A,H2B,H3,H4.
H1
Has one molecule of it bound to DNA as it enters each nuclesome core particle
Chromatin condensation
Varies during the life cycle of the cell. Plays important role in regulating gene expression. In interphase it is euchromatin
Euchromatin
Decondensed chromatin in the nuclease
Heterochromatin
Chromatin in a highly condensed state. Transcriptionally inactive, contains highly repeated DNA sequences
Interphase
Period in cell cycle were genes are transcribed from Euchromatin and DNA is replicated in preperation for mitosis. 10% of DNA is in heterochromatin stage similar to how it is when it undergoes mitosis. Chromatin organized in loops.
Centromeres
Contains highly repeated DNA sequences
DNA during Metaphase
The chromatin organized loops in interphase fold upon themselves to form compact metaphase chromosomes. DNA no longer suitable template for RNA synthesis Transcription stops.
DNA during metaphase cont.
Chromosomes highly condensed (can be seen w/ light microscopy), Packaging of DNA into metaphase chormosomes, highly ordered and reproducible process.
Centromeres
Holds sister chromatids in chromosome together. plays critical role in correct distribution of replicated chromosomes to daughter cells. Site were spindle fibers of microtubles attach to form kinetichore.
Centromeres
Holds sister chromatids in chromosome together. plays critical role in correct distribution of replicated chromosomes to daughter cells. Site were spindle fibers of microtubles attach to form kinetichore. Contains highly repeated DNA sequences
Kinetochore
formed when specific proteins bind to centromeric DNA Mediates spindle fibers attachment to chromosome.
Centromeric Chromatin
Has unique structure, Specially H3 were it is replaced by CENP-A.
CENP-A
the protein that replaces H3 in centromere chromatin nucleosomes in all organisms and is needed for assembly of kinetochore
Epigenetic inheritance
Transfer of Information from parent to progeny not based in DNA. Information norally carried by histones. Centromeric chromatin and its nucleosomes that contain CENP-A
Telomeres
Simple sequence repeat at ends of chromosomes. Plays critical role in replication and maintenance of linear DNA molecules. Contain residues of G on one strand. Sequence TTAGGG. End w/ 3’ single strand overhang. Makes loop at end. Over expressed in Cancer as size means cell death timem left.
Telomere loop
Telomeres binds w/ shelterin and protects from degradation of chromosome termini. Prevents DNA poly from extending DNA here.
Telomerase
Enzyme that uses reverse transcriptase to replicates telomeric DNA sequences.
