Structure and Function of Nucleus: Biology Notes for Competitive Exam

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The nucleus is a crucial part of a cell that controls nearly all of its activities. Cells are broadly classified into two types based on whether they have a nucleus or not – prokaryotic cells do not have a nucleus, while eukaryotic cells have one. This classification helps us understand different types of cells.

What is a Nucleus?

The most important part of a cell is the nucleus (more than one is called nuclei). The word “nucleus” comes from Latin, meaning the “kernel of a nut.”

A nucleus is a vital part of eukaryotic cells, surrounded by a double membrane, and it holds the genetic material.

Nucleus Diagram
Nucleus Diagram (Photo: ScienceFacts)

A diagram shows the different parts of a nucleus. It’s essential to note that only eukaryotic cells have a nucleus, while prokaryotic cells have a nucleoid.

As mentioned earlier, the nucleus is exclusive to eukaryotic cells, setting them apart. However, some cells, like red blood cells (RBCs), don’t have a nucleus, even though they come from eukaryotic organisms.

Also Read: Cells the Unit of Life Complete Overview for Competitive Exam

Structure Of Nucleus

Usually, the nucleus is the most noticeable part of the cell.

  • The nucleus is entirely surrounded by membranes.
  • It is surrounded by a structure called the nuclear envelope.
  • This membrane separates the cytoplasm from the materials inside the nucleus.
  • The cell’s chromosomes are also enclosed within it.
  • DNA is found in the chromosomes, and they hold the genetic information needed to make various cell parts and to reproduce life.

Nucleus Function

The nucleus has important functions:

  • Hereditary Information and Control: It holds the cell’s genetic information and manages the cell’s growth and reproduction.
  • Membrane-Bound Structure: Described as a structure surrounded by membranes, it contains the cell’s genetic material.
  • Active Cellular Processes: Beyond being a storage for DNA, the nucleus is involved in vital cellular activities.
  • DNA Replication: The nucleus enables the duplication of DNA through a process called DNA Replication, creating an exact copy.
  • Cell Division: This duplication is the initial step in cell division, ensuring each new cell has its set of instructions.
  • Transcription Site: The nucleus serves as the site for transcription, generating various types of RNA from DNA. It’s like making copies of specific pages of the body’s instructions that can be read by the rest of the cell.
  • Biology’s Central Rule: Following the fundamental rule of biology, DNA is copied into RNA, and then proteins are formed.

Frequently Asked Questions about the Nucleus

Q1. What important polymer is located in the nucleus?

Answer: The DNA, which is the genetic material of the cell, is a polymer of nucleotides found within the nucleus.

Q2. Can DNA leave the nucleus?

Answer: Eukaryotic DNA does not leave the nucleus but is copied into RNA molecules, which may then travel out of the nucleus.

Q3. What is the difference between a nucleus and a nucleoid?

Answer: A nucleus is a membrane-bound organelle housing DNA in eukaryotes, while a nucleoid is an irregularly shaped region housing genetic material in prokaryotes.

Q4. What is the difference between a nucleus and a nucleolus?

Answer: The nucleus is a membrane-bound organelle containing DNA, while the nucleolus is a sub-organelle within the nucleus responsible for RNA synthesis and ribosome formation.

Q5. What is the nucleus?

Answer: The nucleus is a vital organelle enclosed by a double membrane. It holds genetic material and instructions crucial for cellular processes. This organelle is exclusively present in eukaryotic cells and ranks among the largest in a cell.

Q6. What is the structure of the Nucleus?

Answer: The nucleus features a double-membraned envelope, known as the nuclear membrane. It houses the nucleolus, occupying 25% of the volume. Thread-like structures called chromatins, containing proteins and DNA, are also present. Mechanical strength is provided by the nuclear matrix, a network of fibers similar to the cytoskeleton.

Q7. What are the functions of the nucleus?

Answer: The nucleus serves two primary functions:

  • DNA Storage: It stores the cell’s hereditary material, DNA.
  • Cellular Coordination: The nucleus coordinates essential cellular activities like protein synthesis, cell division, growth, and various other crucial functions.

Q8. How does the nucleus contribute to cell reproduction?

Answer: The nucleus plays a crucial role in cell reproduction by facilitating DNA replication through a process known as DNA Replication. This ensures the creation of identical genetic material, a fundamental step in cell division.

Q9. Can you explain the significance of the nucleolus within the nucleus?

Answer: Certainly. The nucleolus, located within the nucleus, is responsible for the assembly of ribosomes, essential for protein synthesis. It occupies a quarter of the nucleus’s volume, emphasizing its importance in cellular functions.

Q10. Who discovered the cell nucleus?

Answer: The nucleus was first discovered by Antonie van Leeuwenhoek during his study of microorganisms, and its details were further described by Robert Brown in 1831.

Q11. Do prokaryotes have a nucleus?

Answer: Prokaryotic cells, including bacteria and archaea, lack a true nucleus. Instead, they have a membrane-less nucleoid region that contains their free-floating DNA.

Q12. Do archaebacteria and eubacteria have a nucleus?

Answer: Both archaebacteria and eubacteria, being prokaryotic organisms, lack all membrane-bound organelles, including the nucleus.

Q13: Do viruses have a nucleus?

Answer: Viruses do not possess any cell organelles, including a nucleus.

Q14. Do protists have a nucleus?

Answer: Yes, protists, as eukaryotic cells, have a membrane-bound nucleus that houses their genetic material.

Q15. Do fungi and amoeba have a nucleus?

Answer: Yes, fungi and amoeba, being eukaryotes, have a membrane-bound nucleus within their cells.

Q16. Do white blood cells have a nucleus?

Answer: Yes, white blood cells, or leucocytes, have a distinct nucleus that sets them apart from other blood cells.


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