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# Nucleus The nucleus is the most important cell component in living organisms. It is essential for life; cell survival depends on exchanges between the nucleus and cytoplasm. The cell without a nucleus lives for a short time and then degenerates like adult red blood cells. Cell nuclei show varianc...

# Nucleus The nucleus is the most important cell component in living organisms. It is essential for life; cell survival depends on exchanges between the nucleus and cytoplasm. The cell without a nucleus lives for a short time and then degenerates like adult red blood cells. Cell nuclei show variance in shape; this variance has to do with cell shape. It might be spherical, oval, lobed, or irregular, like white blood cells. The nucleus is the largest distinctive organelle inside the cell, and its size differs according to the cell's type. Most cells are mono-nuclear. In some cases, the cell can be di-nuclear, like cartilage cells, liver cells, and muscle cells. The nucleus is central in stem cells. It has a peripheral location in some secretory cells like fatty cells and mucous cells. The nucleus consists of the following components: ## 1. Nuclear Membrane or Envelope - A thin, double-layer membrane. - Surrounds the nucleus and has its own physical and chemical properties. - Regulates the exchange of materials between the nucleus and cytoplasm through micro pores that allow the passage of particles. - This membrane has selective permeability. - It surrounds the nucleus in all cells except for bacteria and blue-green algae (prokaryotic organisms), which have no nucleus but contain nuclear matter. ## 2. Nucleoplasm - A colorless gelatinous liquid that fills the nucleus where the nuclear contents are distributed. - These contents include nucleolus and chromatin network. ## 3. Nucleolus - The nucleus has one or more nucleolus. For example, onion cell nucleus has four nucleoli. - The nucleolus is a relatively large spherical structure inside the nucleus. - It consists of protein and RNA. Nucleolus has a vital role in formation of ribosomes, which are responsible for protein formation. ## 4. Chromatin Network - An interconnected and irregular filamentous structure. - Filaments of the chromatin network appear during cell division, forming a specific number of rod-like structures known as **chromosomes**; they carry genes, which transport genetic features from one generation to another. - Therefore, chromosomes are very important due to their vital role in genetics, reproduction, development, and mutation. - Chromosomes can be seen only during cell division; the number of chromosomes differs in living things. ### Examples - Living beings have a fixed number of chromosomes in their somatic cells. - In **Ascaris lumbricoides**, there are 2 chromosomes only; it is the least number among organisms. - The number of chromosomes in the Spanish butterfly is 380, 12 chromosomes in housefly, 26 chromosomes in frog, 80 chromosomes in pigeon, and 64 chromosomes in horse. For humans, they have 46 chromosomes.