Ribosomes
ரைபோசோம்கள்
Ribosomes are not organelles in the traditional sense; they are molecular machines. They lack a lipid bilayer, yet they are present in every living cell. If you think they are only in the cytoplasm, you are failing the basics of organelle compartmentalization.
The idea
Ribosomes are non-membrane bound organelles composed of RNA and proteins. In eukaryotes, they are 80S, while in prokaryotes, they are 70S. They serve as the exclusive site for protein synthesis. They are found in the cytoplasm, on the Rough Endoplasmic Reticulum, and within mitochondria and chloroplasts.
Why it matters
Protein synthesis is essential for all life processes; ribosomes translate mRNA into functional proteins.
NEET lens
NEET focuses on the Svedberg unit (S) and the specific subunits. Remember: 80S is 60S+40S; 70S is 50S+30S. Do not add the S values. Expect questions on their presence in organelles like mitochondria, which proves the Endosymbiotic Theory.
Clinical significance
Ribosomes are the primary targets for many antibiotics. Drugs like tetracyclines and aminoglycosides bind to bacterial 70S ribosomes to inhibit protein synthesis. This selectivity ensures the pathogen dies while the human 80S ribosomes remain unaffected.
Introduction
Ribosomes are non-membrane bound organelles made of rRNA and proteins, found in both prokaryotes and eukaryotes. They are the site of protein synthesis (translation).
Core concept
Structure: two subunits (large + small). Prokaryote: 70S (50S + 30S subunits). Eukaryote: 80S (60S + 40S subunits). Mitochondria/chloroplast: 70S (like prokaryotes). Location: free in cytoplasm (soluble proteins), on RER (secretory/membrane proteins). Polyribosomes (polysomes): multiple ribosomes on one mRNA simultaneously.
Go deeper
70S vs. 80S distinction is medically important — antibiotics (streptomycin, erythromycin, chloramphenicol) target 70S ribosomes (bacterial) without affecting human 80S ribosomes. This selective toxicity is the basis of antibiotic therapy.
From Class 10
Proteins are made in cells. Ribosomes are the tiny structures where protein synthesis happens.