Which of the following terms describes the DNA-protein complexes that look like beads on a string?
B. 30-nanometer fiber
The correct answer is option D.
The DNA in a human body is folded, wound and compacted into chromosomes so that it can fit in the nucleus. It is organized in a manner that its segments can be reached when needed by specific cell type.
The first stage of organization is the winding of DNA strands around histone proteins. DNA is ordered into structural units which are called nucleosome complexes. These nucleosome complexes control the access of proteins to the regions of DNA.
When we look at this winding of DNA around histone protein through an electron microscope, it resembles small beads on a string. These histone proteins in the form of beads can move along the DNA strand and can change the whole structure of the molecule.
If DNA has to transcribe into RNA, the nucleosomes can slide down the DNA to open the specific chromosomal region. Through this way, it allows RNA polymerase for the transcriptional machinery to initiate the process of transcription.
Nucleosomes can expose DNA segments to open chromosome structure in a controlled manner.
A section of DNA which is wrapped around proteins is called chromosomes. It forms a complex structure with proteins in the nucleus, which is called chromatin. The chromatin allows the DNA to be condensed into a smaller volume.
When this chromatin is viewed under a microscope, the structure resembles beads on a string. Each of these small beads is called a nucleosome which has a diameter of approximately 11 nm. The nucleosome is the fundamental subunit of chromatin.