Explain the structure of protein factories.
GeneralClass 12AllAnswered 27 Mar 2026
Answer
Ribosomes – "Protein Factories"
Structure:
(i) Composition:
- Non-membrane-bound organelles
- rRNA (60%) + ribosomal proteins (40%)
- Chemically: Ribonucleoprotein complex
(ii) Two Subunit Organization:
|
Type |
Large Subunit |
Small Subunit |
Total |
|
Prokaryotic |
50S (23S + 5S rRNA, ~34 proteins) |
30S (16S rRNA, ~21 proteins) |
70S |
|
Eukaryotic |
60S (28S + 5.8S + 5S rRNA, ~49 proteins) |
40S (18S rRNA, ~33 proteins) |
80S |
(iii) Functional Sites:
- A site (Aminoacyl): Accepts incoming aminoacyl-tRNA
- P site (Peptidyl): Holds tRNA with growing peptide chain
- E site (Exit): Release of deacylated tRNA
(iv) Distribution:
- Free in cytoplasm: Synthesize cytoplasmic proteins
- Bound to ER: Synthesize secretory/membrane proteins
- Mitochondria/chloroplasts: 70S type (prokaryotic-like)
Function: Translation (protein synthesis from mRNA template)
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