Anonymous
Jun 30
Describe the structure of Ribosomes and functions in details?
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Jun 30
Ribosomes are complex structures found in all living cells, responsible for protein synthesis. They are composed of two subunits, a large subunit and a small subunit, each made up of proteins and ribosomal RNA (rRNA). The small subunit is responsible for binding to mRNA (messenger RNA), while the large subunit is responsible for catalyzing the formation of peptide bonds between amino acids.
The ribosome functions by reading the genetic code carried by mRNA and translating it into a specific sequence of amino acids, which are then assembled into a protein. This process involves three main steps: initiation, elongation, and termination.
During initiation, the small ribosomal subunit binds to the mRNA and the initiator tRNA (transfer RNA) carrying the amino acid methionine. The large subunit then joins the complex, forming a functional ribosome.
During elongation, the ribosome moves along the mRNA, reading the codons (three-nucleotide sequences) and matching them with the appropriate tRNA carrying the corresponding amino acid. The ribosome catalyzes the formation of peptide bonds between the amino acids, creating a growing polypeptide chain.
During termination, the ribosome reaches a stop codon on the mRNA, signaling the end of protein synthesis. Release factors bind to the ribosome, causing the release of the completed protein and the disassembly of the ribosome complex.
Overall, ribosomes play a crucial role in the synthesis of proteins, which are essential for the structure, function, and regulation of cells. They are found in both the cytoplasm (free ribosomes) and attached to the endoplasmic reticulum (bound ribosomes), where they synthesize proteins for different cellular compartments or for secretion.
The ribosome functions by reading the genetic code carried by mRNA and translating it into a specific sequence of amino acids, which are then assembled into a protein. This process involves three main steps: initiation, elongation, and termination.
During initiation, the small ribosomal subunit binds to the mRNA and the initiator tRNA (transfer RNA) carrying the amino acid methionine. The large subunit then joins the complex, forming a functional ribosome.
During elongation, the ribosome moves along the mRNA, reading the codons (three-nucleotide sequences) and matching them with the appropriate tRNA carrying the corresponding amino acid. The ribosome catalyzes the formation of peptide bonds between the amino acids, creating a growing polypeptide chain.
During termination, the ribosome reaches a stop codon on the mRNA, signaling the end of protein synthesis. Release factors bind to the ribosome, causing the release of the completed protein and the disassembly of the ribosome complex.
Overall, ribosomes play a crucial role in the synthesis of proteins, which are essential for the structure, function, and regulation of cells. They are found in both the cytoplasm (free ribosomes) and attached to the endoplasmic reticulum (bound ribosomes), where they synthesize proteins for different cellular compartments or for secretion.
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Google Gemini AI
Jun 30
Structure of Ribosomes:
Ribosomes are complex macromolecular machines responsible for protein synthesis in cells. They are composed of two subunits:
- Small Subunit (SSU): Also known as the "30S subunit" in prokaryotes and the "40S subunit" in eukaryotes. It contains the 16S rRNA (prokaryotes) or 18S rRNA (eukaryotes) and a set of ribosomal proteins. The SSU binds to messenger RNA (mRNA) and initiates the translation process.
- Large Subunit (LSU): Also known as the "50S subunit" in prokaryotes and the "60S subunit" in eukaryotes. It contains the 23S rRNA (prokaryotes) or 28S rRNA, 5.8S rRNA, and 5S rRNA (eukaryotes) along with numerous ribosomal proteins. The LSU catalyzes the formation of peptide bonds and the elongation of the polypeptide chain.
In prokaryotes, the two subunits are separated when not engaged in protein synthesis. In eukaryotes, they are typically found associated with the endoplasmic reticulum (ER) or as free ribosomes in the cytoplasm.
Functions of Ribosomes:
Ribosomes play a crucial role in the following cellular processes:
1. Translation of mRNA:
- Ribosomes bind to mRNA at the start codon (AUG).
- The small subunit recruits the corresponding transfer RNA (tRNA) molecule carrying the complementary anticodon.
- The large subunit catalyzes the formation of a peptide bond between the amino acid carried by the tRNA and the growing polypeptide chain.
- The tRNA and mRNA move one codon forward, and the process repeats until a stop codon is encountered.
2. Polypeptide Elongation:
- Elongation factors bind to the ribosome and deliver tRNA molecules carrying amino acids that match the codons on the mRNA.
- The large subunit catalyzes the formation of peptide bonds, extending the polypeptide chain.
- The used tRNA molecule is released, and the ribosome advances to the next codon.
3. Peptide Bond Formation:
- The large subunit contains the peptidyl transferase center, which is responsible for catalyzing the formation of peptide bonds between adjacent amino acids.
- The growing polypeptide chain is transferred from one tRNA molecule to the next, creating a linear chain of amino acids.
4. Release of Polypeptide Chain:
- When the stop codon is reached on the mRNA, release factors bind to the ribosome and promote the release of the completed polypeptide chain.
- The ribosome dissociates into its two subunits, and the mRNA and tRNA molecules are recycled for further translation.
5. Regulation of Gene Expression:
- Ribosomes play a role in regulating gene expression by controlling the rate of protein synthesis.
- Factors that bind to ribosomes, such as antibiotics and certain proteins, can inhibit translation and affect gene expression.
Ribosomes are complex macromolecular machines responsible for protein synthesis in cells. They are composed of two subunits:
- Small Subunit (SSU): Also known as the "30S subunit" in prokaryotes and the "40S subunit" in eukaryotes. It contains the 16S rRNA (prokaryotes) or 18S rRNA (eukaryotes) and a set of ribosomal proteins. The SSU binds to messenger RNA (mRNA) and initiates the translation process.
- Large Subunit (LSU): Also known as the "50S subunit" in prokaryotes and the "60S subunit" in eukaryotes. It contains the 23S rRNA (prokaryotes) or 28S rRNA, 5.8S rRNA, and 5S rRNA (eukaryotes) along with numerous ribosomal proteins. The LSU catalyzes the formation of peptide bonds and the elongation of the polypeptide chain.
In prokaryotes, the two subunits are separated when not engaged in protein synthesis. In eukaryotes, they are typically found associated with the endoplasmic reticulum (ER) or as free ribosomes in the cytoplasm.
Functions of Ribosomes:
Ribosomes play a crucial role in the following cellular processes:
1. Translation of mRNA:
- Ribosomes bind to mRNA at the start codon (AUG).
- The small subunit recruits the corresponding transfer RNA (tRNA) molecule carrying the complementary anticodon.
- The large subunit catalyzes the formation of a peptide bond between the amino acid carried by the tRNA and the growing polypeptide chain.
- The tRNA and mRNA move one codon forward, and the process repeats until a stop codon is encountered.
2. Polypeptide Elongation:
- Elongation factors bind to the ribosome and deliver tRNA molecules carrying amino acids that match the codons on the mRNA.
- The large subunit catalyzes the formation of peptide bonds, extending the polypeptide chain.
- The used tRNA molecule is released, and the ribosome advances to the next codon.
3. Peptide Bond Formation:
- The large subunit contains the peptidyl transferase center, which is responsible for catalyzing the formation of peptide bonds between adjacent amino acids.
- The growing polypeptide chain is transferred from one tRNA molecule to the next, creating a linear chain of amino acids.
4. Release of Polypeptide Chain:
- When the stop codon is reached on the mRNA, release factors bind to the ribosome and promote the release of the completed polypeptide chain.
- The ribosome dissociates into its two subunits, and the mRNA and tRNA molecules are recycled for further translation.
5. Regulation of Gene Expression:
- Ribosomes play a role in regulating gene expression by controlling the rate of protein synthesis.
- Factors that bind to ribosomes, such as antibiotics and certain proteins, can inhibit translation and affect gene expression.
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