NUCLEUS
Each cell has got certain specific components called as cell organelles. They make new material and clear out waste from the cell.
Cells can make visible by staining it with safranin, Methylene Blue or Iodine solution.
Upon staining the cytoplasm takes less stain but nucleus stain darker.
Cell comprises of cell wall and protoplasm.
The protoplasm is the fluid living part of cell that includes cytoplasm and nucleus.
Cytoplasm comprises of Cell organelle and cytoskeleton (NO NUCLEUS)
NUCLEUS:
Nucleus can be well defined or not.
Well defined nucleus consists of: Nuclear membrane, Nucleoplasm, Nucleolus, Chromatin.
Nucleus is covered by a double membrane structure called as Nuclear membrane. It can be absent or present.
Organisms with cells having a nuclear membrane are called eukaryotes.
Nuclear membrane comprises of some pores for exchange of material across nucleus.
Chromosomes:
It contains Rod shaped structure called as Chromosomes; they are important for Inheritance of characters from parents to offspring.
Chromosomes are made up of DNA and Proteins.
Nucleic Acid DNA contains all the necessary information.
Functional unit of the DNA is called as Genes.
DNA is present in form of chromatin.
Upon division chromatin turned to chromosome.
The nucleus plays a central role when single cell divides and forms two new cells.
In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane. They are called as Prokaryotes.
Prokaryotes also lack cell organelles.
Undefined nuclear region containing only nucleic acids is called a nucleoid.
The chlorophyll in photosynthetic prokaryotic bacteria is associated with membranous vesicles (bag like structures) but not with plastids as in eukaryotic cells
Difference between Prokaryote cell and Eukaryote cell:
Why membrane is significant?
The significance of membranes can be illustrated with the example of viruses. Viruses lack any membranes and hence do not show characteristics of life until they enter a living body and use its cell machinery to multiply.
Nucleus comprises of several distinct subdomains means nucleus has several different parts inside it, each with its own role. These subdomains are:
Nucleoplasm: Contains Chromatin: Heterochromatin (Highly condensed/less active) and Euchromatin (less condensed/active)
Nucleolus: Site for r-RNA formation.
Nuclear speckles and Cajal bodies
Small nuclear structures are present inside nucleus that helps in assemble of several RNAs that may together forms Spliceosome, they are nucleases that removes introns by slicing, these regions are nuclear speckles region.
Similar large nuclear structures the Cajal bodies are present inside the nucleus. They are involved in transport and maturation of small RNA involved in RNA splicing and formation of r-RNA.
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