BOTANY WITH THE BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

V. CYTOLOGY. THE CONCEPT OF THE CELL

Structure of the Plant Cell

The Nucleus

The Nucleus measures approximately 2-8 мкм in size. In an active Cell, it consists of a double-membrane envelope, nucleoplasm (nuclear sap, karyolymph, karyoplasm), Chromatin, and one or more nucleoli. The nuclear envelope has two membranes, each 8 nm thick, separated by a perinuclear space about 15 nm wide. The nuclear envelope contains pores 30-100 nm in diameter that facilitate the Transport of substances between the hyaloplasm and the nucleoplasm. The nuclear membrane is connected to the membranes of The Endoplasmic reticulum, forming a continuous system with it.

During mitosis and Cell Division, the nuclear envelope breaks down into cisternae of the Endoplasmic reticulum and is reconstituted from them after division. The nucleoplasm contains the nucleolus and Chromosomes. The latter are clearly visible during nuclear and cell division. During interphase, chromosomes are decondensed and form the so-called chromatin network.

Chromosomes contain the majority of the Genetic information that regulates cellular activity. Each species is characterized by a constant number and Structure of chromosomes, known as the karyotype. Chromosomes consist of a single long DNA molecule and several million histone protein molecules.

At the onset of cell division, each chromosome consists of two longitudinal chromatids, which become single-chromatid structures by the end of division.

The nucleolus is a nuclear structure involved in The formation of ribosomal subunits. It is spherical in shape. Its central part is denser and represented by fibrillar material of chromosomal origin—specifically, chromosomal regions known as the nucleolar organizer. The central core of the nucleolus is surrounded by a less dense region composed of ribosomal subunits.

Three states of the nucleus are distinguished in The Cell, corresponding to its three main Functions.

The interphase nucleus, in which METABOLISM/36.html">DNA Replication takes place, resulting in the formation of a second chromatid and the Transformation of a single-chromatid chromosome into a two-chromatid one.

The dividing nucleus, in which the two-chromatid chromosome splits into single-chromatid ones, which are then distributed between the daughter nuclei. This ensures the transmission of hereditary information.

The active (working) nucleus, in which genes localized in the chromosomes regulate cellular activity.