12-3 RNA and Protein Synthesis Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Comparing The transcription process is similar to replication. Transcription and replication both involve complex enzymes and complementary base pairing. The two processes have different end results. Replication copies all the DNA; transcription copies a gene. Replication makes one copy; transcription can make many copies. Copyright Pearson Prentice Hall

12–3 RNA and Protein Synthesis Genes are coded DNA instructions that control the production of proteins. Genetic messages can be decoded by copying part of the nucleotide sequence from DNA into RNA. RNA contains coded information for making proteins. Copyright Pearson Prentice Hall

12–3 RNA and Protein Synthesis RNA carries DNA’s instructions. The central dogma states that information flows in one direction from DNA to RNA to proteins. Copyright Pearson Prentice Hall 4

12–3 RNA and Protein Synthesis The central dogma includes three processes. Replication Transcription Translation RNA is a link between DNA and proteins. Copyright Pearson Prentice Hall 5

Copyright Pearson Prentice Hall The Structure of RNA The Structure of RNA There are three main differences between RNA and DNA: The sugar in RNA is ribose instead of deoxyribose. RNA is generally single-stranded instead of double stranded. RNA contains uracil in place of thymine. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA Types of RNA There are three main types of RNA: messenger RNA ribosomal RNA transfer RNA Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA Ribosome Ribosomal RNA The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes. Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA Amino acid The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Transfer RNA During protein construction, transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome. Copyright Pearson Prentice Hall

Protein Synthesis DNA molecule DNA strand (template) 3¢ 5¢ TRANSCRIPTION mRNA 5¢ 3¢ Codon TRANSLATION Protein Amino acid

Copyright Pearson Prentice Hall Transcription Transcription A transcription complex consisting of RNA and other proteins recognizes the start site of a gene and begins to unwind the DNA. RNA polymerase reads one side of the DNA template and strings together a complementary strand of RNA nucleotides. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Transcription Transcription The growing RNA strand hangs freely as it is transcribed and detaches completely once the entire gene is transcribed. DNA Molecule Nucleotides Newly synthesized RNA strand RNA polymerase Copyright Pearson Prentice Hall 13

Copyright Pearson Prentice Hall Transcription RNA RNA polymerase DNA During transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code The Genetic Code The genetic code is the “common language” of mRNA instructions and is shared by almost all organisms. The code is written using four “letters” (the bases: A, U, C, and G). Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid. The start codon signals the start of translations and the amino acid methionine. The stop codon is three codons that signal the end of a chain of amino acids. A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code The genetic code matches each codon to its amino acid or function. three stop codons one start codon, codes for methionine The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward. Copyright Pearson Prentice Hall 18

Copyright Pearson Prentice Hall Translation Translation Translation is the decoding of an mRNA message into a polypeptide chain (protein). Ribosomes are the site of protein synthesis; made of rRNA and proteins Catalyzes the formation of peptide bonds between amion acids During translation, the cell uses information from messenger RNA to produce proteins. Nucleus mRNA Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Reading frame Codon A reading frame is the series of 3 nonoverlapping nucleotides read, in order, by a cell. 3 different reading frames are possible for each mRNA molecule. Codons must be read in the correct reading frame for the correct protein to be made. This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits. Copyright Pearson Prentice Hall 20

Copyright Pearson Prentice Hall Anticodon Amino acids are linked to become a protein. An anticodon is a set of three nucleotides that is complementary to an mRNA codon. An anticodon is carried by a tRNA. Transfer RNA (tRNA) is a type of RNA that carries amino acids from the cytoplasm to the ribosome. One end has a specific anticodon, the other end attaches to a specific amino acid. This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits. Copyright Pearson Prentice Hall 21

Copyright Pearson Prentice Hall Ribosomes Ribosomes consist of two subunits The large subunit has three binding sites for tRNA. The small subunit binds to mRNA. This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits. Copyright Pearson Prentice Hall 22

Copyright Pearson Prentice Hall Translation Process 1. Ribosome assembles at the start codon; complementary tRNA molecule pair with the exposed codon. Lysine Phenylalanine tRNA Methionine Ribosome During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Start codon Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Translation Protein Synthesis-ribosome helps bond the new amino acid to the start codon and breaks the bond between the amino acid and the first tRNA. Lysine tRNA During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Translation direction Ribosome Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Translation 3. Ribosome pulls the RNA strand the length of one codon; first tRNA returns to the cytoplasm; another codon is exposed for tRNA binding. The process continues until the ribosome reaches a stop codon. Polypeptide Ribosome tRNA During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Copyright Pearson Prentice Hall

Amino acids within a polypeptide Genes and Proteins Codon Codon Codon DNA mRNA Protein Single strand of DNA Codon Codon Codon mRNA This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits. Alanine Arginine Leucine Amino acids within a polypeptide Copyright Pearson Prentice Hall 26

Amino acid (Start codon methionine) Polypeptide bond Large subunit tRNA codons Small subunit mRNA anticodon

Copyright Pearson Prentice Hall 12–3 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 The role of a master plan in a building is similar to the role of which molecule? messenger RNA DNA transfer RNA ribosomal RNA Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 A base that is present in RNA but NOT in DNA is thymine. uracil. cytosine. adenine. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 The nucleic acid responsible for bringing individual amino acids to the ribosome is transfer RNA. DNA. messenger RNA. ribosomal RNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the intron. exon. promoter. codon. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 A codon typically carries sufficient information to specify a(an) single base pair in RNA. single amino acid. entire protein. single base pair in DNA. Copyright Pearson Prentice Hall

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