When PSII receives more light than PSI, plastoquinone becomes predominantly reduced, resulting in activation of the LHCII kinase. The kinase phosphorylates LHCII, resulting in migration of LHCII away from the granal region where it can associate with PSI, thereby adjusting the relative excitation of PSII and PSI.

TLS Online TPP Program

#Id: 4023

#Unit 2. Cellular Organization

In most regions, the fibers are much less densely packed than in the mitotic chromosome. This material is called euchromatin. It has a relatively dispersed appearance in the nucleus and occupies most of the nuclear region.

TLS Online TPP Program

#Id: 4024

#Unit 2. Cellular Organization

Some regions of chromatin are very densely packed with fibers, displaying a condition comparable to that of the chromosome at mitosis. This material is called heterochromatin.

TLS Online TPP Program

#Id: 4033

#Unit 2. Cellular Organization

In some cases, the various heterochromatic regions, especially those associated with centromeres, aggregate into a densely staining chromocenter.

The common form of heterochromatin that always remains heterochromatic is called constitutive heterochromatin. 

It is permanently condensed. 

It replicates late in S phase and has a reduced frequency of genetic recombination relative to euchromatic gene rich areas of the genome.

TLS Online TPP Program

#Id: 4042

#Unit 2. Cellular Organization

In contrast, there is another category of heterochromatin, called facultative heterochromatin, in which regions of euchromatin are converted to a heterochromatic state.

TLS Online TPP Program

#Id: 4043

#Unit 2. Cellular Organization

When mitotic chromosomes are subjected to proteolytic enzyme (trypsin) treatment followed by staining with the chemical dye Giemsa, they generate distinct chromosome-specific patterns called G-bands.

p (short; after the French petit) or q (long; for queue, the French word for tail)

TLS Online TPP Program

#Id: 4044

#Unit 2. Cellular Organization

In G-banding, chromosomes are first gently heated and then exposed to Giemsa stain; this DNA dye preferentially darkens certain regions to produce alternating dark and light G bands. Each G band is a very large segment of DNA from 1 to 10 Mb in length, containing many loops. With high-resolution G-banding techniques, a standard diploid human karyotype of 46 chromosomes is seen to contain hundreds of dark and light G bands. Not used in plants.