MECHANISM OF EUKARYOTIC CHROMOSOME PACKAGING

an intricate structure that allows the extensive length of DNA to be efficiently organized within the nucleus of a cell.

Eukaryotic Chromosome Packaging

__________ is composed of two strands that form a double helix. Each strand consists of ____________

DNA, nucleotides

Each nucleotide contains a _____________, _____________, __________

phosphate group, deoxyribose (sugar), and Nitrogenous base

1. nitrogenous bases of DNA

2. For RNA

1. Adenine, Thymine, Cytosine, or Guanine

2. Uracil

The total length of DNA in a single human cell is approximately ___________ Hence, it must be compacted to fit within a nucleus that is only about ______ micrometers in diameter.

2 meters

6

DNA is made of nucleotide sequences that act as instructions. These instructions are organized into __________ that codes for proteins or functional RNAs

genes

Packaging level arangement

DNA → Nucleosomes (histones + DNA) → 30-nm fiber→ Chromatin → chromatin loop → Rosettes of chromatin Loops → chromosomes

The fundamental unit of chromatin

Nucleosome

Nucleosomes consist of a core of _____ proteins around which DNA is wrapped.

histone

Approximately ________ of DNA are wrapped around this histone octamer leading to the creation of a structure that resembles "beads-on-a-string".

146 bp

The core histones include __, ___, ___, ____ all forming an octamer.

H2A, H2B, H3, H4

________ a strand of DNA that connects adjacent nucleosomes, typically consists of about ___________

Linker DNA, 20-80 bp

in total, nucleosome folding shortens the DNA by ____ folds

7-fold

packaging controls DNA _______ that is important for ________, ________, and __________

accessibility that is important for transcription, replication, and repair

___________ binds at nucleosome entry/exit points and promotes their fiber formation.

Linker histones

Structural models of 30-nm fiber

1. Nucleosomes are arranged in a helical pattern, tightly wound coil

2. Alternate across the fiber, forming a more linear, two-start helix with linker DNA crossing the fiber exterior

1. solenoid

2. zigzag

__________ form chromatin loops anchored to _________

30 nm fibers; protein scaffholds

Type of scaffold proteins

1. The SMC complex

2. Resolves super coils and DNA entanglements

3. Drives the mitotic chromosome condensation

4. Mediates sister chromatid cohesion and loop extrusion

1. Cohesin;condensin

2. Topoisomerases

3. Condesin

4. Cohesin

Linker Histones is also noted as ________ it binds to the DNA at the entry and exit points of the nucleosome.

H1