How is the coiling of long DNA fiber achieved?

DNA packaging is a crucial process that enables long DNA molecules to fit inside the small space of the cell nucleus. This process is essential for the successful transmission of genetic information from one cell to another during cell division.

The coiling of DNA fibers is achieved through a process called chromatin organization. The primary level of DNA packaging is achieved by wrapping DNA around proteins called histones, which results in the formation of nucleosomes. Nucleosomes are considered the basic building blocks of chromatin.

Each nucleosome comprises a core of eight histone proteins, including two copies of H2A, H2B, H3, and H4, around which the DNA is wrapped. The DNA between nucleosomes is referred to as linker DNA.

Further coiling and folding of nucleosomes result in the formation of higher-order chromatin structures, which ultimately lead to the formation of chromosomes. Although the precise mechanisms that underlie the coiling and folding of DNA into chromosomes are not fully understood, scientists believe that the process involves a combination of histone modifications, chromatin remodeling complexes, and various other proteins that interact with DNA.

 

Nucleosomes

DNA is associated with basic protein molecules called histones. DNA and histone become organized into nucleoprotein fibers. When stretched out a nucleoprotein looks like a beaded chain under the electron microscope. Each “bead” in a chain is a nucleosome. It is 10 nm in diameter. Each nucleosome is an aggregate of eight histone molecules (octamere), of two types (as seen in the figure). The nucleosome is repeated after every 200 nucleotides of the DNA.

Spacer or linker DNA

The nucleosome “beads” in a chromatin appear to be held together by segments of DNA called linker DNA or spacer DNA, which stretch from one nucleosome to the next.

 

Super Coils

Further coiling of the DNA occurs, when the string of nucleosome wraps into higher order coils called super coil, (200 nm diameters).

DNA packing in a Eukaryotic Chromosome 

Chromatin

The super coil network is called chromatin. Chromatin forms super coils within the chromosomes. Highly condensed portion of chromatin is called heterochromatin. Some of these portions remain permanently condensed. The part of the chromosome which is condensed only during cell division is called euchromatin.

Nucleosome

The genome is defined as a set of genes in a cell or living things. The human genome comprises 3.2 billion DNA letter or base pairs, as announced by Human Genome Consortium in April, 2003. Human genome is thought to carry between 50000 and 100000 genes which codes for various proteins.

#Nucleosomes #DNAPackaging #Histones #NucleoproteinFibers #ChromatinStructure #ElectronMicroscopeImaging #LinkerDNA #SpacerDNA #SuperCoils #DNACoiling #Chromosomes #Heterochromatin #Euchromatin #HumanGenome #DNABasePairs #GeneticInformation #OctamereHistoneMolecules #DNAOrganization #ChromatinCondensation #GenomeSequencing #DNAStructure #ProteinCodingGenes #DNAReplication #CellDivision #ChromatinPackaging #ChromosomeStructure #HumanGenomeConsortium #DNASequencing #GeneticComplexity #ChromatinDynamics