Eukaryotic Cell Structure I Function

Eukaryotic Cell: Structure and Function

Introduction

Eukaryotic cells are more complex and organized than prokaryotic cells. They possess a true nucleus enclosed by a nuclear membrane and contain membrane-bound organelles, each specialized for different cellular functions. Eukaryotic cells make up all multicellular organisms (plants, animals, fungi) and some unicellular organisms (protozoa, algae).

Structure of Eukaryotic Cells

A eukaryotic cell consists of three major components:

1. Plasma Membrane – Outer boundary controlling the exchange of substances.
2. Cytoplasm – Fluid medium containing organelles and facilitating biochemical reactions.
3. Nucleus – Houses genetic material (DNA) and controls cellular activities.

Each eukaryotic organelle has a specific function, contributing to the cell’s complexity and efficiency.

Components and Functions of a Eukaryotic Cell:

[1] Plasma Membrane (Cell Membrane)

• Structure: A phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.
• Functions:
  • Selective permeability – regulates the entry/exit of substances.
  • Cell communication – via receptor proteins.
  • Cell recognition – glycoproteins and glycolipids act as markers.

 

[2] Cytoplasm

• Structure: Semi-fluid substance (cytosol) containing organelles, enzymes, and nutrients.
• Functions:
  • Provides a medium for biochemical reactions.
  • Supports and protects organelles.

 

[3] Nucleus (Control Center of the Cell)

• Structure:
  • Enclosed by a nuclear envelope (double membrane).
  • Contains nucleoplasm with DNA, RNA, and proteins.
  • Has nucleolus, where ribosomes are synthesized.
  • Nuclear pores allow exchange of materials between the nucleus and cytoplasm.
• Functions:
  • Houses DNA (chromosomes), which carries genetic information.
  • Controls cell growth, metabolism, and reproduction.

 

[4] Endoplasmic Reticulum (ER) (Transport System)

ER is a network of tubules and sacs involved in protein and lipid synthesis.

(a) Rough Endoplasmic Reticulum (RER)

• Structure: Studded with ribosomes.
• Functions:
  • Synthesizes proteins for export or use in the cell membrane.

(b) Smooth Endoplasmic Reticulum (SER)

• Structure: Lacks ribosomes, smooth in appearance.
• Functions:
  • Synthesizes lipids and steroids.
  • Detoxifies harmful substances (in liver cells).
  • Stores calcium ions (in muscle cells).

 

[5] Ribosomes (Protein Factories)

• Structure: Small, non-membranous organelles composed of rRNA and proteins.
• Location: Found freely in the cytoplasm or attached to the RER.
• Functions:
  • Protein synthesis for cellular functions and export.

 

[6] Golgi Apparatus (Packaging and Transport)

• Structure: A stack of flattened sacs (cisternae).
• Functions:
  • Modifies, sorts, and packages proteins and lipids.
  • Forms lysosomes and secretory vesicles.

 

[7] Lysosomes (Cellular Digestion)

• Structure: Membrane-bound vesicles containing digestive enzymes.
• Functions:
  • Breaks down waste materials and cellular debris.
  • Helps in autophagy (self-digestion of damaged organelles).
  • Aids in immune defense by digesting harmful bacteria.

 

[8] Peroxisomes (Oxidative Enzymes)

• Structure: Small membrane-bound vesicles containing oxidative enzymes like catalase.
• Functions:
  • Break down fatty acids and detoxify hydrogen peroxide (H₂O₂).

 

[9] Mitochondria (Powerhouse of the Cell)

• Structure: Double-membrane organelle with inner folds (cristae) and a matrix containing enzymes.
• Functions:
  • Generates ATP (Adenosine Triphosphate) through cellular respiration.
  • Contains its own DNA and can self-replicate.

 

[10] Cytoskeleton (Cell Shape and Movement)

• Structure: A network of protein filaments (microtubules, microfilaments, and intermediate filaments).
• Functions:
  • Maintains cell shape.
  • Assists in cell division (mitosis).
  • Facilitates intracellular transport.

 

[11] Centrosomes and Centrioles (Cell Division)

• Structure: A pair of centrioles surrounded by a matrix.
• Functions:
  • Organizes spindle fibers during cell division.

 

[12] Cilia and Flagella (Cell Motility)

• Structure:
  • Cilia: Short, hair-like structures.
  • Flagella: Long, whip-like tail (e.g., sperm cells).
• Functions:
  • Cilia: Moves substances over cell surfaces (e.g., in respiratory tract).
  • Flagella: Provides movement.

 

Special Organelles in Plant Cells:

[13] Cell Wall (Rigid Support)

• Structure: Composed of cellulose in plants, chitin in fungi.
• Functions:
  • Provides structural support and prevents osmotic lysis.

 

[14] Vacuoles (Storage & Osmoregulation)

• Structure: Large, membrane-bound sac filled with water, nutrients, and waste products.
• Functions:
  • Maintains turgor pressure in plant cells.
  • Stores nutrients and waste.

[15] Chloroplasts (Photosynthesis in Plants & Algae)

• Structure:
  • Double-membrane organelle containing chlorophyll.
  • Has thylakoids stacked into grana.
• Functions:
  • Captures sunlight to produce glucose via photosynthesis.