Question
Explain what are ribosomes and how they work.
Answers
GPT-4o mini
Ribosomes are complex molecular machines found within all living cells that play a critical role in the process of protein synthesis, also known as translation. They are composed of ribosomal RNA (rRNA) and proteins, forming two subunits: a large subunit and a small subunit. These subunits come together during the process of translation.
### Structure of Ribosomes
1. **Subunits**:
- In eukaryotic cells, ribosomes are typically 80S ribosomes, comprising a large (60S) subunit and a small (40S) subunit.
- In prokaryotic cells, ribosomes are smaller, generally 70S ribosomes, which consist of a large (50S) subunit and a small (30S) subunit.
2. **Components**: Ribosomes contain rRNA, which plays a crucial role in catalyzing the formation of peptide bonds between amino acids. The ribosomal proteins provide structural support and help stabilize the ribosome's shape.
### Function of Ribosomes
Ribosomes are essential for translating messenger RNA (mRNA) into polypeptides (chains of amino acids), which then fold into functional proteins. The process of translation can be broken down into several key steps:
1. **Initiation**:
- The small ribosomal subunit binds to the mRNA molecule at the start codon (AUG), which signals the beginning of translation.
- An initiator tRNA (transfer RNA) carrying the amino acid methionine recognizes the start codon and binds to it.
- The large ribosomal subunit then joins the small subunit, forming a complete ribosome ready for translation.
2. **Elongation**:
- During this phase, tRNAs bring amino acids to the ribosome based on the sequence of codons in the mRNA. Each tRNA has an anticodon that is complementary to the mRNA codon, ensuring that the correct amino acid is added to the growing polypeptide chain.
- The ribosome has three key sites during this phase:
- **A site (Aminoacyl site)**: Where the incoming tRNA carrying the next amino acid binds.
- **P site (Peptidyl site)**: Where the tRNA carrying the growing polypeptide chain is located.
- **E site (Exit site)**: Where empty tRNA molecules exit the ribosome after delivering their amino acids.
- The ribosome catalyzes the formation of peptide bonds between adjacent amino acids, lengthening the polypeptide chain.
3. **Termination**:
- The process continues until a stop codon (UAA, UAG, or UGA) on the mRNA is reached.
- There are no corresponding tRNA molecules for stop codons, which triggers the release factors to bind to the ribosome.
- This causes the ribosomal subunits to disassemble, and the newly synthesized polypeptide is released, folding into its functional three-dimensional shape.
### Summary
In summary, ribosomes are vital cellular structures responsible for synthesizing proteins by decoding the information carried by mRNA. Their ability to facilitate the interaction between mRNA and tRNA, and to catalyze peptide bond formation, makes them essential for the expression of genes and the functioning of all living cells.
### Structure of Ribosomes
1. **Subunits**:
- In eukaryotic cells, ribosomes are typically 80S ribosomes, comprising a large (60S) subunit and a small (40S) subunit.
- In prokaryotic cells, ribosomes are smaller, generally 70S ribosomes, which consist of a large (50S) subunit and a small (30S) subunit.
2. **Components**: Ribosomes contain rRNA, which plays a crucial role in catalyzing the formation of peptide bonds between amino acids. The ribosomal proteins provide structural support and help stabilize the ribosome's shape.
### Function of Ribosomes
Ribosomes are essential for translating messenger RNA (mRNA) into polypeptides (chains of amino acids), which then fold into functional proteins. The process of translation can be broken down into several key steps:
1. **Initiation**:
- The small ribosomal subunit binds to the mRNA molecule at the start codon (AUG), which signals the beginning of translation.
- An initiator tRNA (transfer RNA) carrying the amino acid methionine recognizes the start codon and binds to it.
- The large ribosomal subunit then joins the small subunit, forming a complete ribosome ready for translation.
2. **Elongation**:
- During this phase, tRNAs bring amino acids to the ribosome based on the sequence of codons in the mRNA. Each tRNA has an anticodon that is complementary to the mRNA codon, ensuring that the correct amino acid is added to the growing polypeptide chain.
- The ribosome has three key sites during this phase:
- **A site (Aminoacyl site)**: Where the incoming tRNA carrying the next amino acid binds.
- **P site (Peptidyl site)**: Where the tRNA carrying the growing polypeptide chain is located.
- **E site (Exit site)**: Where empty tRNA molecules exit the ribosome after delivering their amino acids.
- The ribosome catalyzes the formation of peptide bonds between adjacent amino acids, lengthening the polypeptide chain.
3. **Termination**:
- The process continues until a stop codon (UAA, UAG, or UGA) on the mRNA is reached.
- There are no corresponding tRNA molecules for stop codons, which triggers the release factors to bind to the ribosome.
- This causes the ribosomal subunits to disassemble, and the newly synthesized polypeptide is released, folding into its functional three-dimensional shape.
### Summary
In summary, ribosomes are vital cellular structures responsible for synthesizing proteins by decoding the information carried by mRNA. Their ability to facilitate the interaction between mRNA and tRNA, and to catalyze peptide bond formation, makes them essential for the expression of genes and the functioning of all living cells.