Q.What is true about ribosomes?

Ribosomes are ribonucleoprotein particles made of rRNA and protein, present in all cells (prokaryotic and eukaryotic), and are the site of protein synthesis.

Let's check each statement:

• (a) is incorrect: prokaryotic ribosomes are 70S (made of a 50S and a 30S subunit), not 80S. 80S is the eukaryotic ribosome size (60S + 40S subunits).
• (b) is correct: every ribosome, whether 70S or 80S, is composed of ribosomal RNA (rRNA) combined with a set of ribosomal proteins. …

Prokaryotic ribosomes are 70S, made of a 50S large subunit and a 30S small subunit.

Ribosome size is measured by sedimentation coefficient (Svedberg units, S), which reflects size/density rather than adding arithmetically. Prokaryotes (bacteria) have smaller 70S ribosomes composed of a 50S and a 30S subunit, found free in the cytoplasm. Eukaryotic cytoplasmic ribosomes are larger, 80S (60S + 40S subunits) -- though eukaryotic organelles like mitochondria and chloroplasts retain 70S ribosomes, consiste …

70S ribosomes occur in prokaryotes and in mitochondria/chloroplasts of eukaryotic cells.

Ribosomes are classified by their sedimentation coefficient (S, Svedberg unit). Prokaryotic cells (bacteria, cyanobacteria) have 70S ribosomes, composed of a 50S large subunit and 30S small subunit. Interestingly, the organelles of endosymbiotic origin — mitochondria and chloroplasts — inside eukaryotic cells also contain their own 70S ribosomes (supporting the endo …

A polysome is a single mRNA strand with multiple ribosomes attached along its length, each independently translating it into a protein — an efficient way to mass-produce a protein from one transcript.

During protein synthesis (translation), a ribosome attaches near the 5' end of an mRNA strand and moves along it, reading the codons and adding amino acids to a growing polypeptide chain. Because the mRNA is much longer than the space occupied by a single ribosome, several ribosomes can attach to and move along the SAME mRNA one after another, each at a different stage of translating the same message.

This string of ribosomes strung along one mRNA, viewed under an electron microscope, looks like beads on a string, and is called a polysome or polyribosome.

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