Nucleus, Definition, Structure, Function, Diagram

 The nucleus is one of the most important parts of a cell . Often referred to as the "control center" of the cell, it contains genetic material and plays a key role in controlling many cellular activities. The nucleus is absent in bacteria and blue-green algae. As a fundamental topic in biology, the structure and function of the nucleus are essential for students preparing for the NEET Exam  , which it forms a crucial part of the NEET syllabus .

Definition of Nucleus

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Discovery of Nucleus

Structure of Nucleus

• • Nuclear Envelope: The nucleus is surrounded by a double membrane known as the nuclear envelope. This envelope acts like a protective barrier, separating the contents of the nucleus from the rest of the cell. It has two layers:

• Outer membrane

• Inner membrane

• • • These two layers have tiny openings called nuclear pores. The pores are very important because they allow certain materials, like RNA and proteins, to move in and out of the nucleus while keeping the DNA safe inside.
  • Chromatin : The nucleus contains chromosomes, each made up of a single DNA molecule combined with an equal amount of proteins. Together, the DNA and associated proteins form chromatin.
    • The majority of these proteins are histones, which are basic proteins rich in positively charged amino acids like arginine and lysine. These positive charges help them bind tightly to the negatively charged phosphate groups of DNA.
    • Chromatin also includes smaller amounts of non-histone proteins, mostly transcription factors, which temporarily associate with DNA to help regulate gene expression.

• Chromatin is of two types:

• • • Heterochromatin: Highly condensed and inactive, located near the nuclear membrane.
    • Euchromatin: Loosely packed and active in transcription, found abundantly in cells.
• Nucleoplasm: Inside the nuclear envelope is a jelly-like substance called the nucleoplasm (or nuclear sap). It fills the space within the nucleus and helps keep all the components inside the nucleus suspended and functional.
• Nucleolus : The nucleolus is a round structure inside the cell's nucleus that mainly makes and assembles ribosomes. It is also where ribosomal RNA genes are copied. After ribosomes are assembled, they move to the cell’s cytoplasm, where they help produce proteins

Functions of Nucleus

• Managing Genetic Information : The nucleus stores the cell’s DNA, which carries genetic instructions. This information determines the inherited traits of an organism and controls how cells function.
• Protein and Enzyme Production : The nucleus regulates the synthesis of proteins and enzymes by controlling which genes are expressed, guiding the cell to produce necessary molecules for its functions.
• Cell Division and Growth : The nucleus plays a key role in cell division (mitosis and meiosis) by ensuring the correct replication and distribution of DNA, allowing the organism to grow and reproduce.
• Storage of DNA, RNA, and Ribosomes : The nucleus safely stores DNA, houses RNA involved in protein synthesis, and produces ribosomes in the nucleolus, which are essential for building proteins.
• Regulating mRNA Transcription : The nucleus controls the transcription of DNA into mRNA, which carries the genetic code to ribosomes for protein synthesis.
• Ribosome Production : The nucleolus within the nucleus creates ribosomes, which are critical for translating genetic information into proteins that the cell needs for various functions.

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MCQs of Nucleus

Q1. Which of the following is NOT found in the nucleus?

1. DNA
2. RNA
3. Ribosomes
4. Chromosomes

Q2. Which of the following is the function of the nucleus?

1. Energy production.
2. Waste removal.
3. DNA storage and replication.
4. Protein synthesis.

Q3. What is the function of histones in the nucleus?

1. Structural support
2. DNA replication
3. RNA synthesis
4. Protein synthesis

MCQs Answers of Nucleus