21 6 The Genetic Code and Protein Synthesis

Protein Synthesis, Transcription The RNA in a cell facilitates the synthesis of proteins in

Protein Synthesis, Transcription 2. m. RNA leaves the nucleus and attaches to a ribosome,

Genetic Code The genetic code consists of sets of three nucleotides (triplets) in m.

Codons and Amino Acids To determine the amino acid sequence coded in the following

The Genetic Code: m. RNA Codons General, Organic, and Biological Chemistry: Structures of Life,

Protein Synthesis, Activation 3. Molecules of t. RNA pick up specific amino acids according

Protein Synthesis, Initiation and Chain Elongation 4. A start codon binds the first t.

Protein Synthesis, Termination 5. Eventually, a ribosome encounters a stop codon with no corresponding

Complementary Sequences Table 21. 8 summarizes the nucleotide and amino acid sequences in protein

Study Check Write the amino acids coded for by a section of m. RNA

Solution Write the amino acids coded for by a section of m. RNA with

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21. 6 The Genetic Code and Protein Synthesis The function of the different types of RNA in the cell is to facilitate the task of synthesizing proteins. An activated t. RNA with anticodon AGU bonds to serine at the acceptor stem. Learning Goal Use the genetic code to write the amino acid sequence for a segment of m. RNA. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Protein Synthesis, Transcription The RNA in a cell facilitates the synthesis of proteins in the following steps: 1. Genetic information encoded in DNA is transcribed and processed into mature m. RNA molecules. These molecules move out of the nucleus to the ribosomes in the cytosol. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Protein Synthesis, Transcription 2. m. RNA leaves the nucleus and attaches to a ribosome, where the genetic information in the m. RNA is translated into a sequence of amino acids in a protein. Core Chemistry Skill Writing the Amino Acid for an m. RNA Codon General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Genetic Code The genetic code consists of sets of three nucleotides (triplets) in m. RNA called codons that specify the amino acids and their sequence in the protein. • There is a different codon for all 20 amino acids needed to build a protein. The genetic code • has stop signals, UGA, UAA, and UAG, that signal the termination of protein synthesis. • has a start codon, AUG, that signals the start of protein synthesis. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Codons and Amino Acids To determine the amino acid sequence coded in the following section of an m. RNA, 5′ CCU AGC GGA CUU 3′ 1. refer to the genetic code for the identity of the amino acids CCU = Proline AGC = Serine GGA = Glycine CUU = Leucine 2. m. RNA section codes for the amino acid sequence are written in the following order: Pro—Ser—Gly—Leu General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Protein Synthesis, Activation 3. Molecules of t. RNA pick up specific amino acids according to their anticodons. t. RNA activation occurs when the correct amino acid is attached to each t. RNA. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Protein Synthesis, Initiation and Chain Elongation 4. A start codon binds the first t. RNA carrying the amino acid methionine to the m. RNA. As the ribosome moves along the m. RNA, a new amino acid forms a peptide bond to the growing protein chain. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Protein Synthesis, Termination 5. Eventually, a ribosome encounters a stop codon with no corresponding t. RNAs, which signals the termination of polypeptide synthesis and its release from the ribosome. t. RNA reenters the pool of free t. RNA, ready to be recharged with a new amino acid. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Complementary Sequences Table 21. 8 summarizes the nucleotide and amino acid sequences in protein synthesis. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check Write the amino acids coded for by a section of m. RNA with the following base sequence: 5ʹ GCC GUA GAC 3ʹ Some possible codons to use are the following: GGC = Glycine GAC = Aspartic acid CUC = Leucine GUA = Valine GCC = Alanine CGC = Arginine General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Write the amino acids coded for by a section of m. RNA with the following base sequence: 5ʹ GCC GUA GAC 3ʹ Ala—Val—Asp General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.