Chap#3|Nucleus|Nuclear envelope|Nucleolus|FSc biology part 1|New Edition Book

Описание: Here’s a clear, exam-oriented and detailed summary of Chapter 3: Nucleus, Nuclear Envelope & Nucleolus for FSc Biology Part I (New Edition Book).
🌟 Chapter 3 – The Nucleus
The nucleus is the most important and largest organelle found in eukaryotic cells. It acts as the control center of the cell.
📌 1. Definition of Nucleus
The nucleus is a spherical or oval organelle bounded by a membrane, containing genetic information (DNA) that regulates all cellular activities including growth, metabolism, and reproduction.
📌 2. History
Discovered by Robert Brown (1831) in plant cells.
Called the “nucleus” because it seemed like the core or center of the cell.
📌 3. Structure of the Nucleus
The nucleus has several main parts:
A) Nuclear Envelope
B) Nucleoplasm
C) Chromatin / Chromosomes
D) Nucleolus
🧱 A. Nuclear Envelope
✅ Definition
A double membrane that surrounds the nucleus and separates it from the cytoplasm.
📌 Structure
Composed of two lipid bilayers:
Outer nuclear membrane
Inner nuclear membrane
Between them is the perinuclear space.
❗ Features
✔ Nuclear pores:
Tiny openings in the envelope.
Allow transport of molecules (like RNA and proteins) between nucleus and cytoplasm.
✔ Outer membrane is continuous with the rough endoplasmic reticulum (RER).
✔ Inner membrane supported by protein network called nuclear lamina.
📌 Functions
Protects the genetic material (DNA).
Controls the movement of substances in and out of the nucleus.
Maintains the shape and structure of nucleus.
🧪 B. Nucleoplasm
The semi-fluid matrix inside the nucleus.
Contains chromatin, nucleolus, and nuclear solutes.
🧬 C. Chromatin and Chromosomes
Chromatin:
Long, thread-like DNA + protein complex.
During cell division, chromatin condenses into chromosomes.
Chromosomes:
Carry hereditary information.
Each species has a specific number (e.g., humans have 46).
🌑 D. Nucleolus (Plural: Nucleoli)
✅ Definition
A dense, spherical structure inside the nucleus where ribosomal RNA (rRNA) is made.
📌 Features
Not surrounded by a membrane.
May be one or more per nucleus.
Visible clearly during interphase.
📌 Functions
✔ Ribosomal RNA (rRNA) synthesis
✔ Assembly of ribosomal subunits
✔ Plays a role in protein synthesis indirectly.
📌 Summary Table
Component
Structure
Function
Nuclear Envelope
Double membrane with pores
Protects DNA & controls transport
Nucleoplasm
Jelly-like fluid inside nucleus
Medium for nuclear activities
Chromatin / Chromosomes
DNA + proteins
Genetic material, inheritance
Nucleolus
Dark region without membrane
rRNA synthesis & ribosome assembly
📌 Key Points for FSc Exams
✔ Nucleus is the control center of the cell.
✔ Nuclear envelope has two membranes and nuclear pores.
✔ Nucleolus makes rRNA and assembles ribosomes.
✔ Chromatin changes to chromosomes during cell division.