11.2 Chromosome structure and compaction Flashcards
How is DNA in a cell if it is stretched out?
about 6 feet/ 2 meters long
What are the three levels of chromosome compaction?
- Nucleosome
- Supercoiling
- Radial loop- scaffold
give the function of nucleosomes
function: Condense naked DNA 7-fold to a 100A fiber.
The basic unit of DNA packaging in eukaryotes, where DNA wraps around histone proteins. This compact structure helps organize DNA and regulate gene expression.
Give the function of supercoiling
causes an additional 6-fold compaction, achieving a 40- to 50-fold condensation relative to naked DNA.
Further twists the DNA, creating a more compact form that reduces its size, which is essential for fitting DNA into the cell and managing twisting stress during replication and transcription.
What is the function of radial loop-scaffolding ?
Through progressive compaction of 300A fiber, condenses DNA to rodlike miotic chromosomes that are 10 000 times more compact than naked DNA.
A higher-order structure where loops of DNA are anchored to a protein scaffold. This arrangement compacts the DNA further and is critical for organizing chromosomes, especially during cell division.
What structure is the fundamental unit of chromosomal packaging?
Nucleosome
What is the structure of nucleosomes?
they resemble beads on a string ( histones forming the core and DNA wound around them)
In what two ways do spacing and structure of nucleosomes affect genetic function?
- Accessibility for proteins that initiate transcription, replication and further compaction
- Arrangement along chromatin is highly defined and varies in different cell types and under different conditions.
The nucleosome core is an ___________ of two each of the histones; H2B, H2B, H3, and H4
octamer
explain the wrapping process of DNA around histones:
160bp of DNA wraps twice around a nucleosome core. 40 bp of linker DNA connects adjacent nucleosomes. Histone H1 associated with linker DNA as it enters and leaves the nucleosome core. DNA bends sharply at several places as it wraps around the core histone octamer. Base sequence dictates preferred nucleosome positions along the DNA.
100A nucleosomal chromatin i compacted into 300A fiber by ___________
supercoiling
Explain the radial loop-scaffold model for higher level of compacting
Several nonhistone proteins(NHPs) bind to chromatin every 60-100 kb and tether the 300A fiber into structural loops. Other NHPs gather several loops together into daisy-like rosettes. Condensins may further condense chromosomes into a compact bundle for mitosis.
The karyotype of a human female is examined by ?
high-resolution G-banding
explain high-resolution G-banding
Metaphase chromosomes that are stained with Giemsa. The chromosomes have alternating bands of light and dark staining. Each band contains many DNA loops and ranges from 1 to 10 Mb in length. Banding patterns on each chromosome are highly reproducible.
The location of genes on a chromosome is related to?
chromosomal bands
