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Questions and Answers
How are prokaryotic ribosomes structured?
Prokaryotic ribosomes are constructed from proteins and ribosomal RNA (rRNA), with a size of 70S.
What is the function of ribosomes in prokaryotic cells?
Ribosomes function as a workbench for protein synthesis (translation).
How do ribosomes contribute to protein synthesis in prokaryotic cells?
Ribosomes join amino acids to form a polypeptide chain during protein synthesis.
What is the purpose of inclusions in prokaryotic cells?
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What distinguishes prokaryotic ribosomes from eukaryotic cytoplasmic ribosomes?
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Study Notes
Prokaryotic Ribosome Structure
- Prokaryotic ribosomes are composed of two subunits: a small 30S subunit and a large 50S subunit.
- The 30S subunit is made up of a 16S rRNA molecule and 21 proteins.
- The 50S subunit is comprised of a 5S rRNA, a 23S rRNA, and 34 proteins.
Prokaryotic Ribosome Function
- Ribosomes are essential for protein synthesis in prokaryotic cells.
- They act as the site of translation, where mRNA is decoded into a polypeptide chain.
Protein Synthesis Process
- The mRNA binds to the 30S subunit, positioning the start codon at the P-site.
- The initiation complex, consisting of the 30S subunit, mRNA, and initiator tRNA, then joins with the 50S subunit to form a complete ribosome.
- The tRNA molecules carrying specific amino acids enter the A-site, and peptide bonds are formed between the amino acids.
- The ribosome moves along the mRNA, reading codons and adding amino acids to the growing polypeptide chain.
Prokaryotic Inclusions
- Prokaryotic cells can store various substances within inclusions, which are non-membrane-bound compartments.
- These inclusions can store nutrients like glycogen or polyhydroxybutyrate, provide buoyancy with gas vesicles, or store inorganic compounds like sulfur granules.
Distinguishing Prokaryotic and Eukaryotic Ribosomes
- Prokaryotic ribosomes are smaller than eukaryotic cytoplasmic ribosomes (70S vs 80S).
- Prokaryotic ribosomes have a distinct sedimentation coefficient (Svedberg unit) compared to eukaryotic ribosomes.
- This difference in size and sedimentation coefficient arises from the rRNA and proteins present in each type of ribosome.
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Test your knowledge about cellular inclusions like volutin granules and storage forms of carbon, as well as the structure and characteristics of chromosomes in cell biology.