Ribosomes: Structure, Types & Functions

Introduction

Ribosomes are small, non-membrane-bound organelles found in all living cells. They are the sites of protein synthesis, making them essential for cell growth, repair, and metabolism.

Discovery

Ribosomes were discovered by George Emil Palade and are also known as Palade particles.

Structure of Ribosomes

• Ribosomes are composed of ribosomal RNA (rRNA) and proteins • They have two subunits – large and small • Not surrounded by a membrane • Found either free in cytoplasm or attached to rough endoplasmic reticulum

Types of Ribosomes

1. 70S Ribosomes

• Found in prokaryotes • Also present in mitochondria and chloroplasts of eukaryotes • Made of 50S (large) + 30S (small) subunits

2. 80S Ribosomes

• Found in eukaryotic cytoplasm • Made of 60S (large) + 40S (small) subunits

Location of Ribosomes

• Free ribosomes – synthesize proteins used inside the cell • Bound ribosomes – synthesize proteins for secretion or membranes

Functions of Ribosomes

1. Protein synthesis

2. Help in enzyme formation

3. Essential for growth and repair

4. Support metabolic activities

Ribosomes vs Lysosomes (Quick Comparison)

• Ribosomes: Protein synthesis • Lysosomes: Digestion and waste removal

Diagram (To be added)

Labeled diagram of ribosome structure

Key Points for Exams

• Ribosomes are non-membranous • Present in both prokaryotic and eukaryotic cells • Called protein factories of the cell • rRNA plays a catalytic role

5 MCQs

1. Ribosomes are the site of: A) Respiration
B) Protein synthesis
C) Digestion
D) Transport

Answer: B

2. Ribosomes are composed of: A) DNA & proteins
B) rRNA & proteins
C) Lipids & proteins
D) Enzymes only

Answer: B

3. 80S ribosomes are found in: A) Prokaryotes
B) Mitochondria
C) Eukaryotic cytoplasm
D) Chloroplast

Answer: C

4. Who discovered ribosomes? A) Robert Hooke
B) Watson
C) Palade
D) Golgi

Answer: C

5. Ribosomes attached to RER synthesize: A) Cytoplasmic proteins
B) Secretory proteins
C) Lipids
D) ATP

Answer: B