Chapter 4 - Section 4.2 - Study Guide - Assess Your Learning Outcomes - Page 137: 7

**Genetic Translation:** Genetic translation is the process by which the information encoded in the mRNA (messenger RNA) molecule is used to synthesize a protein. It occurs in the ribosomes, cellular structures responsible for protein synthesis. Translation involves multiple steps and requires the participation of several key molecules, including mRNA, tRNA, and ribosomes. Here's an overview of the process and the roles of these molecules: **Process of Genetic Translation:** 1. **Initiation:** - Translation begins with the binding of the small ribosomal subunit to the mRNA molecule at a specific site known as the start codon. In humans, the start codon is typically AUG, which codes for the amino acid methionine. - An initiator tRNA molecule, carrying methionine, binds to the start codon through complementary base pairing between the tRNA's anticodon and the mRNA codon. 2. **Elongation:** - During the elongation phase, the ribosome moves along the mRNA in a 5' to 3' direction. As the ribosome advances, it reads each mRNA codon and facilitates the binding of the corresponding aminoacyl-tRNA (tRNA carrying the correct amino acid). - The ribosome forms peptide bonds between adjacent amino acids carried by tRNA molecules, creating a growing polypeptide chain. 3. **Translocation:** - After each peptide bond formation, the ribosome advances to the next mRNA codon, and the tRNA from the previous codon is released. This process is called translocation. - The tRNA that carried the growing polypeptide chain is shifted to the P (peptidyl) site, while the next aminoacyl-tRNA occupies the A (aminoacyl) site of the ribosome. 4. **Termination:** - Translation continues until a stop codon (UAA, UAG, or UGA) is encountered in the mRNA. Stop codons do not code for any amino acids but signal the termination of protein synthesis. - When a stop codon is reached, a release factor protein binds to the ribosome, leading to the hydrolysis of the bond between the polypeptide chain and the final tRNA. - The newly synthesized protein is released from the ribosome, and the ribosome dissociates from the mRNA. **Outcome of Genetic Translation:** The primary outcome of genetic translation is the synthesis of a functional protein. The sequence of amino acids in the protein is determined by the sequence of codons in the mRNA. The folded structure of the protein determines its function, and proteins are involved in a wide range of cellular processes. **Roles of mRNA, tRNA, and Ribosomes in Translation:** 1. **mRNA (Messenger RNA):** - mRNA carries the genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm or endoplasmic reticulum, where protein synthesis occurs. - The sequence of codons in mRNA provides the template for specifying the order of amino acids in the protein. 2. **tRNA (Transfer RNA):** - tRNA molecules are adapter molecules that transport amino acids to the ribosome during translation. - Each tRNA has an anticodon that can base-pair with a complementary mRNA codon. The amino acid carried by the tRNA corresponds to the codon it recognizes. 3. **Ribosomes:** - Ribosomes are the cellular structures responsible for carrying out translation. They consist of two subunits, a small subunit and a large subunit. - Ribosomes facilitate the binding of mRNA, tRNA, and amino acids, as well as the formation of peptide bonds between amino acids. - They move along the mRNA, reading the codons and catalyzing the assembly of the polypeptide chain. In summary, genetic translation is the process of synthesizing proteins from the information encoded in mRNA. It involves initiation, elongation, and termination phases, with the roles of mRNA, tRNA, and ribosomes being crucial for the accurate and efficient synthesis of proteins. This process is essential for gene expression and the production of functional cellular components.

**Genetic Translation:** Genetic translation is the process by which the information encoded in the mRNA (messenger RNA) molecule is used to synthesize a protein. It occurs in the ribosomes, cellular structures responsible for protein synthesis. Translation involves multiple steps and requires the participation of several key molecules, including mRNA, tRNA, and ribosomes. Here's an overview of the process and the roles of these molecules: **Process of Genetic Translation:** 1. **Initiation:** - Translation begins with the binding of the small ribosomal subunit to the mRNA molecule at a specific site known as the start codon. In humans, the start codon is typically AUG, which codes for the amino acid methionine. - An initiator tRNA molecule, carrying methionine, binds to the start codon through complementary base pairing between the tRNA's anticodon and the mRNA codon. 2. **Elongation:** - During the elongation phase, the ribosome moves along the mRNA in a 5' to 3' direction. As the ribosome advances, it reads each mRNA codon and facilitates the binding of the corresponding aminoacyl-tRNA (tRNA carrying the correct amino acid). - The ribosome forms peptide bonds between adjacent amino acids carried by tRNA molecules, creating a growing polypeptide chain. 3. **Translocation:** - After each peptide bond formation, the ribosome advances to the next mRNA codon, and the tRNA from the previous codon is released. This process is called translocation. - The tRNA that carried the growing polypeptide chain is shifted to the P (peptidyl) site, while the next aminoacyl-tRNA occupies the A (aminoacyl) site of the ribosome. 4. **Termination:** - Translation continues until a stop codon (UAA, UAG, or UGA) is encountered in the mRNA. Stop codons do not code for any amino acids but signal the termination of protein synthesis. - When a stop codon is reached, a release factor protein binds to the ribosome, leading to the hydrolysis of the bond between the polypeptide chain and the final tRNA. - The newly synthesized protein is released from the ribosome, and the ribosome dissociates from the mRNA. **Outcome of Genetic Translation:** The primary outcome of genetic translation is the synthesis of a functional protein. The sequence of amino acids in the protein is determined by the sequence of codons in the mRNA. The folded structure of the protein determines its function, and proteins are involved in a wide range of cellular processes. **Roles of mRNA, tRNA, and Ribosomes in Translation:** 1. **mRNA (Messenger RNA):** - mRNA carries the genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm or endoplasmic reticulum, where protein synthesis occurs. - The sequence of codons in mRNA provides the template for specifying the order of amino acids in the protein. 2. **tRNA (Transfer RNA):** - tRNA molecules are adapter molecules that transport amino acids to the ribosome during translation. - Each tRNA has an anticodon that can base-pair with a complementary mRNA codon. The amino acid carried by the tRNA corresponds to the codon it recognizes. 3. **Ribosomes:** - Ribosomes are the cellular structures responsible for carrying out translation. They consist of two subunits, a small subunit and a large subunit. - Ribosomes facilitate the binding of mRNA, tRNA, and amino acids, as well as the formation of peptide bonds between amino acids. - They move along the mRNA, reading the codons and catalyzing the assembly of the polypeptide chain. In summary, genetic translation is the process of synthesizing proteins from the information encoded in mRNA. It involves initiation, elongation, and termination phases, with the roles of mRNA, tRNA, and ribosomes being crucial for the accurate and efficient synthesis of proteins. This process is essential for gene expression and the production of functional cellular components.