21 5 RNA and Transcription A typical ribosome

21. 5 RNA and Transcription A typical ribosome consists of a small subunit and a large subunit. The subunit shapes shown contain both protein and r. RNA. Learning Goal Identify the different types of RNA; describe the synthesis of m. RNA. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

RNA and DNA RNA • makes up most of the nucleic acid found in the cell. • transmits genetic information from DNA to operate the cell. • has several types as shown below. • differs from DNA in the following ways: • The sugar in RNA is ribose; the sugar in DNA is deoxyribose. • The base uracil replaces thymine. • RNA molecules are single stranded; DNA molecules are double stranded. • RNA molecules are much smaller than DNA molecules. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Types of RNA There are three major types of RNA: • 5% of RNA is messenger RNA (m. RNA), which carries genetic information from DNA to the ribosomes. • 15% of RNA is transfer RNA (t. RNA), which translates the genetic information in m. RNA into the amino acid sequence for the protein. • 80% of RNA is ribosomal RNA (r. RNA), which is the most abundant type of RNA; it is combined with proteins to form ribosomes. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

t. RNA A typical t. RNA molecule • can be drawn as a two-dimensional cloverleaf. • shows more twists that illustrate the L-shape of t. RNA in the three-dimensional model. • has an acceptor stem at the 3′ end with the nucleotide sequence ACC where an enzyme attaches an amino by forming an ester bond with the free — OH group. • contains an anticodon, which is a series of three bases that complements three bases on m. RNA. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

t. RNA Structure (a) A two-dimensional model of t. RNA is represented as a cloverleaf. (b) The three-dimensional model of RNA has more twists that shows its L-shape. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

RNA and Protein Synthesis In the nucleus, genetic information for protein synthesis • is copied from a gene in DNA. • makes m. RNA in a process called transcription. The m. RNA molecules move out of the nucleus into the cytosol, where they bind with the ribosomes. The t. RNA molecules convert the information in the m. RNA into amino acids in a process called translation. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

RNA and Protein Synthesis The genetic information in DNA is replicated in cell division and used to produce messenger RNA that codes for amino acids used in protein synthesis at the ribosomes. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Transcription: Synthesis of m. RNA In transcription, a section of DNA containing the gene unwinds. • RNA polymerase uses the DNA template strand to form the new m. RNA using bases that are complementary to the DNA template. • An m. RNA is synthesized using complementary base pairing, with uracil (U) replacing thymine (T). • The newly formed m. RNA moves out of the nucleus to ribosomes in the cytoplasm. Core Chemistry Skill Writing the m. RNA Segment for a DNA Template General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Transcription: Synthesis of m. RNA DNA undergoes transcription when RNA polymerase makes a complementary copy of a gene using the 3′ to 5′ DNA template strand. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

m. RNA Processing: Exons, Introns In eukaryotes, • DNA contains exons that code for proteins and introns that do not code for proteins. • a pre-RNA is formed that includes the noncoding introns. • the noncoding introns are removed. • the exons are joined to form m. RNA, which goes to the ribosomes with the information for the synthesis of protein. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

m. RNA Processing: Exons, Introns A pre-m. RNA, containing copies of the exons and introns from the gene, is processed to remove the introns to form a mature m. RNA that codes for a protein. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Regulation of Transcription Regulation of m. RNA syntheses is controlled at the transcription level by a specific m. RNA that is synthesized when the cell requires a particular protein. • The transcription of a gene requires the RNA polymerase to bind to DNA in plants and animals. • A group of protein complexes called a transcription factor must recognize and bind to promoter segments. • Other proteins, called activators, bind with the transcription factor complex to increase the rate of RNA transcription. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Regulation of Transcription factors at the promoter region bind RNA polymerase to DNA, which activates the transcription of a gene. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check What is the sequence of bases in m. RNA produced from a section of the template strand of DNA that has the sequence of bases 3′ C T A A G G 5′? 1) 5′ G A T T C C 3′ 2) 5′ G A U U C C 3′ 3) 5′ C T A A G G 3′ General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution What is the sequence of bases in m. RNA produced from a section of the template strand of DNA that has the sequence of bases 3′ C T A A G G 5′? 2) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.