Lecture 5 Reading Flashcards
Mitotic chromosomes
Highly condensed chromosomes in a dividing cell
Karyotype
The display of 46 human chromosomes at mitosis
What three types of specialized nucleotide sequences in DNA contorl replication, separation and partition into daughter cells
DNA replication origin
Centromere
Telomere
Replication origin
Nucleotide sequence
The location at which duplication of DNA begins
Centromere
Nucleotide sequence
Allows one copy of each duplicated and condensed chromosome to be pulled into a daughter cell when a cell divides
Kinetochore
Protein complex forms at centromere and attaches duplicated chromosomes to the mitotic spindle so they can be pulled apart
Telomere
The ends of a chromosome
Contain repeated nucleotide sequences that enable ends of chromosomes to be efficiently replicates
Form structures that protect the end of the chromosome from being mistaken by the cell for a broken DNA molecule that needs repair
Proteins that bind to dna to form eukaryotic chromosomes 2
Histones
Non histone chromosomal proteins
Chromatin
Complex of histone and non histone chromosomal protein with nuclear dna if eukaryotic cells
Nucleosome
Most basic level of chromosome packing
Linker DNA
Exposed dna between nucleosome core particles
Histone octamer
Forms a protein core around which the double stranded DNA is wound
Nucleosomes repeat at intervals of
About 200 nucleotide pairs
Epigeneric inheritance
A form of inheritance that is superimposed on the genetic inheritance based on DNA
Two types of chromatin
Heterochromatin - highly condensed
Euchromatin - not as condensed
Position effect
Chromosome breakage and rejoining that translocate normally euchromatic DNA into the neighborhood of heterochromatin
Position effect variegation
Once a heterochromatin condition is established on a piece of chromatin, it tends to be stably inherited by all of the cell’s progeny
How is DNA packaged
DNA tightly wrapped in a left handed coil of 1.7 turns. All four of the histones that make up core of nucleosome are small proteins. They share a structural motif known as the histone fold, which is formed from three alpha helices connected by two loops.
How large is interface between DNA and histones
142 h bonds formed between DNA and histone core in each nucleosome, half of these bonds form bet. The amino acid backbone of the histones and the sugar phosphate backbone of dna. Hydrophobic interactions and salt linkages also hold dna and protein together in nucleosome. More than one fifth of a, acids in histones is lysine or arginine, positive charges neutralize dna backbone which is negative.
Chromatin remodeling complexes
Include a subunit that Hydrolyzes ATP. Subunit binds to protein core of nucleosome and to double stranded dna that winds around it. ATP hydrolysis releases energy to move Dna and changes structure of nucleosome.
Linker stone
Histone H1 larger than individual core histones. Single h1 binds to each nucleosome contacting dna and protein, and changing path of dna as it exits from the nucleosome.
How are core histones covalently modified
Acetylation of lysines, mono, di and trimethylation of lysines, and phosphorylation of serines. Occur on unstructured n-terminal histone tails that protrude from nucleosome. Are reversible.
Histone acetyl transferase
Adds acetyl groups to lysines
Histone deacetylate complexes
Remove acetyl groups from lysines
Histone methyl Transferases and histone demethylases
Add and remove methyl groups
What does acetylation of lysine cause
Loosens chromatin structure, removes lysine’s positive charge and affinity of tails for adjacent Nucleosomes,
Most profound effect of histone modification
Their ability to recruit specific other proteins to the modified stretch of chromatin. Recruited proteins act with modified histones to determine how and when genes will be expressed, as well as other chromosomal functions.
Histone variants
Histones extra of standard core histones
When are major histones made? Variants?
S phase. Interphase.
Histone code
Combination known to have specific meaning for the cell in the sense that they determine how and when DNA in Nucleosomes is to be accessed
Reader complex
Protein domains linked together as modules in a single large protein or protein complex, which thereby recognizes a specific combo of histone modifications
Lampbrush chromosomes
Stiff and enormously extended chromosomes in growing amphibians. Paired in preparation for meiosis, clearly visible in light microscope.
Polytene cells of flies
Fruit fly drosophila
Multiple cycles of dna synthesis make cell unusually large. Polyploid cells.
Polytene chromosomes
Copies of each chromosome are aligned side by side to create thse giant chromosomes
What happens to a gene when it is highly expresses
It’s position in interior of nucleus changes
Nucleolus
Ribosome unit formation site
Canal bodies and inter chromatin granule clusters
Organelles inside nucleus of plant and animal cells
Nuclear matrix or scaffold
Insoluble material left in nucleus after a series of biochemical extraction steps
Purposes of compaction during mitosis
When condensation complete, sister chromatids have been disentangled
Compaction of chromosomes protects the relatively fragile dna molecules from being broken as they are pulled apart
When does condensation of interphase chromosomes into mitotic chromosomes begin
In early M phase. Connected with progression of cell cycle. Gene expression shuts during M phase.
Cohesive and condensins
Aid compaction of chromosomes
