Cell biology - NUCLEOLUS, NUCLEOPLASM, CHROMATIN.pptx

About nucleoplasm, nucoleolus and chromatin

1. NUCLEOLUS, NUCLEOPLASM, CHROMATIN -DHARSHAN K

2. NUCLEOLUS The nucleolus is the distinct structure present in the nucleus of eukaryotic cells. Primarily, it participates in assembling the ribosomes, alteration of transfer RNA and sensing cellular stress. The nucleolus is composed of RNA and proteins, which form around specific chromosomal regions.

3. Structure of the Nucleolus In eukaryotic cells, nucleolus has a well-ordered structure with four main ultrastructural components. The components can be further identified as: Fibrillar Centers: It is the place where the ribosomal proteins are formed. Granular Components: Before ribosomes are formed, these components have rRNA that binds to ribosomal proteins. Dense Fibrillar Components: It has new transcribed RNA, which connects to the ribosomal proteins. Nucleolar vacuoles: It is present only in plant cells. The ultrastructure of the nucleolus can be easily visualized through an electron microscope.  The arrangement of the nucleolus within the cell can be clearly studied by the techniques –  fluorescent recovery after photobleaching and fluorescent protein tagging. The nucleolus of several plant species has very high concentrations of iron in contrast to the human and  animal cell  nucleolus. Nucleolus Function The nucleolus is considered as the brain of the nucleus, covering nearly 25% volume of the nucleus. Primarily, it takes part in the production of subunits that unites to form ribosomes. Hence, nucleolus plays an important role in the synthesis of proteins and in the production of ribosomes in eukaryotic cells.

4. NUCLEOPLASM Nucleoplasm is a type of protoplasm that is composed of thick fluid and constitutes chromatin fibres made up of DNA and usually found in the nucleus of the eukaryotic cells. This fluid contains primarily water, dissolved ions, and a complex mixture of molecules. Its primary function is to act as a suspension medium for the organelles of the nucleus.

5. The nucleoplasm includes the  chromosomes  and nucleoli. Many substances such as nucleotides and enzymes, which direct activities that take place in the nucleus are dissolved in the nucleoplasm. The soluble, liquid portion of the nucleoplasm is called the nucleosol or nuclear hyaloplasm. Nucleoplasm also called nuclear sap or karyoplasm. Other functions of nucleoplasm include the maintenance of nuclear shape and structure, and the transportation of ions, molecules, and other substances important to cell metabolism and function. It is a highly gelatinous, sticky liquid that supports the chromosomes and nucleoli. A soluble, fluid component of the nucleoplasm is called the nuclear hyaloplasm. Nucleoplasm is found inside the nucleus and resembles cytoplasm is some aspects. It is composed mostly of water, nucleoplasm also has an array of complex components. However, the difference between cytoplasm and nucleoplasm is that nucleoplasm consists of such materials including nucleotide making them useful in the preparation of RNA and DNA and also the enzymes that influence the building reactions of DNA and RNA. All these substances and components present inside the cell membrane together are considered as nucleoplasm and hence it comprises of the nucleus, cell fluids, and the organelles. The principal function of the nucleoplasm is to program as a suspension substance for the organelles inside the nucleus. It also helps to maintain the shape and structure of the nucleus and plays an important role in the transportation of materials that are vital to cell metabolism and function .

6. CHROMATIN Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. Nuclear DNA does not appear in free linear strands; it is highly condensed and wrapped around nuclear proteins in order to fit inside the nucleus.Chromatin exists in two forms. One form, called euchromatin, is less condensed and can be transcribed. The second form, called heterochromatin, is highly condensed and is typically not transcribed.

7. Under the microscope in its extended form, chromatin looks like beads on a string. The beads are called nucleosomes. Each nucleosome is composed of DNA wrapped around eight proteins called histones. The nucleosomes are then wrapped into a 30 nm spiral called a solenoid, where additional histone proteins support the chromatin structure. During cell division, the structure of the chromatin and chromosomes are visible under a light microscope, and they change in shape as the DNA is duplicated and separated into two cells. The primary protein components of chromatin are  histones , which bind to DNA and function as "anchors" around which the strands are wound. In general, there are three levels of chromatin organization: DNA wraps around histone proteins, forming  nucleosomes  and the so-called  beads on a string  structure ( euchromatin ). Multiple histones wrap into a 30- nanometer  fiber consisting of nucleosome arrays in their most compact form ( heterochromatin ). Higher-level  DNA supercoiling  of the 30-nm fiber produces the  metaphase  chromosome (during mitosis and meiosis).