Chapter 11 Flashcards
(25 cards)
What two proteins help sufficient compaction of DNA?
- histone protein
2. non-histone chromosomal protein
Chromatin
generic term for any complex of DNA and protein found in a cell’s nucleus
What is the makeup of chromatin?
- 1/3 DNA
- 1/3 histone
- 1/3 non-histone proteins
- significant amount of RNA
histones
relatively small protein with a preponderance of the basic, positively charged amino acids lysine and arginine
What are the five types of core histone that makeup the nucelosome?
H1, H2A, H2B, H3, and H4
Nucelosome
rudimentary DNA packaging unit; composed of DNA wrapped around a histone protein core
What roles do nonhistone chromosomal proteins have?
- structural roles
- helps package DNA into more complex structures
- form the structural backbone of the chromosome
- DNA polymerase
- motor proteins that aid in chromosome segregation
- foster or regulate transcription and RNA processing during gene expression
linker DNA
an addition of 40 or so base pairs that connects one nucleosome with the next
What is the function of the H1 protein?
It lies outside the core associating with DNA entering and leaving the nucelosome
What are the several models proposed to explain levels of compaction?
- nucleosome supercoiling
- radial loop-scaffold model
Nucleosome supercoiling model
proposes that the 100A nucleosomal chromatin supercoils into a 300 A superhelic, achieving a further six-fold chromatin condensation
Radial loop-scaffold model
proposes that several nonhistone proteins bind to chromatin every 60-100kb and tether the supercoiled, nucleosome into structural loops forming loops into daisy-like rosettes and then compressing the rosette centers into a compact bundle
condensins
a multisubunit complex of proteins in eukaryotic cells that compacts during mitosis
G-band
alternating dark and light segments (1-10Mb) of a chromosome after staining with Giesma dye
idiograms
diagrams of the banding pattern
heterochromatin
darker regions
euchromatin
lighter regions
constitutive heterochromatin
chromosomal regions that remain condensed in heterochromatin at most times in cells
position-effect variegation (PEV)
variable expression of a gene in a population of cells, caused by the gene’s location near highly compacted heterochromatin
barrier insulators
block the spread of heterochromatin
noncoding RNA (ncRNA)
never leaves the nucleus and is never translated into a protein
replicon
also called replication unit
-the DNA running both ways from one origin of replication to the endpoints where it merges with DNA from adjoining replication forks
telomeres
protective caps of chromsomes
What kinds of somatic cells in our bodies can make telomerase and have the potential to reproduce for many generations?
- Stem cells
- Tumor cells
