From DNA to Proteins Chapter 14

Marvelous Mussel Adhesive Marvelous Mussel Adhesive Mussel binds itself to rocks with threads coated with the protein bysuss Mussel binds itself to rocks with threads coated with the protein bysuss Gene for bysuss has been put into yeast Gene for bysuss has been put into yeast Yeast synthesize the protein based on the instructions in the mussel DNA Yeast synthesize the protein based on the instructions in the mussel DNA

Same two steps produce all proteins: 1) DNA is transcribed to form RNA Occurs in the nucleus Occurs in the nucleus RNA moves into cytoplasm RNA moves into cytoplasm 2) RNA is translated to form polypeptide chains, which fold to form proteins Steps from DNA to Proteins

Three Classes of RNAs Messenger RNA Messenger RNA Carries protein-building instruction Carries protein-building instruction Ribosomal RNA Ribosomal RNA Major component of ribosomes Major component of ribosomes Transfer RNA Transfer RNA Delivers amino acids to ribosomes Delivers amino acids to ribosomes

A Nucleotide Subunit of RNA A Nucleotide Subunit of RNA phosphate group sugar (ribose) uracil (base) Figure 14.2 Page 228

Base Pairing during Transcription DNA RNAG C A T C G T A G C A U C G T A base pairing in DNA replicationbase pairing in transcription

Transcription & DNA Replication Like DNA replication Like DNA replication Nucleotides added in 5’ to 3’ direction Nucleotides added in 5’ to 3’ direction Unlike DNA replication Unlike DNA replication Only small stretch is template Only small stretch is template RNA polymerase catalyzes nucleotide addition RNA polymerase catalyzes nucleotide addition Product is a single strand of RNA Product is a single strand of RNA

Promoter A base sequence in the DNA that signals the start of a gene A base sequence in the DNA that signals the start of a gene For transcription to occur, RNA polymerase must first bind to a promoter For transcription to occur, RNA polymerase must first bind to a promoter

Gene Transcription transcribed DNA winds up again DNA to be transcribed unwinds mRNA transcript RNA polymerase Figure 14.4c Page 229

Adding Nucleotides growing RNA transcript 5’ 3’ 5’ 3’ direction of transcription Figure 14.4d Page 229

Genetic Code Set of 64 base triplets Set of 64 base triplets Codons Codons 61 specify amino acids 61 specify amino acids 3 stop translation 3 stop translation Figure 14.7 Page 230

tRNA Structure codon in mRNA anticodon amino acid OH amino-acid attachment site Figure 14.8 Page 231

Ribosomes tunnel small ribosomal subunitlarge ribosomal subunitintact ribosome Figure 14.9b,c Page 231

Three Stages of Translation Initiation InitiationElongationTermination

Initiation Initiator tRNA binds to small ribosomal subunit Initiator tRNA binds to small ribosomal subunit Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG “start” codon Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG “start” codon Large ribosomal subunit joins complex Large ribosomal subunit joins complex Fig a-c Page 232

Binding Sites binding site for mRNA P (first binding site for tRNA) A (second binding site for tRNA) Figure 14.10d Page 232

Elongation mRNA passes through ribosomal subunits mRNA passes through ribosomal subunits tRNAs deliver amino acids to the ribosomal binding site in the order specified by the mRNA tRNAs deliver amino acids to the ribosomal binding site in the order specified by the mRNA Peptide bonds form between the amino acids and the polypeptide chain grows Peptide bonds form between the amino acids and the polypeptide chain grows

Elongation Fig e-g Page 233

Termination Stop codon into place Stop codon into place No tRNA with anticodon No tRNA with anticodon Release factors bind to the ribosome Release factors bind to the ribosome mRNA and polypeptide are released mRNA and polypeptide are released new polypeptide chain mRNA Fig j-k Page 233

What Happens to the New Polypeptides? Some just enter the cytoplasm Some just enter the cytoplasm Many enter the endoplasmic reticulum and move through the cytomembrane system where they are modified Many enter the endoplasmic reticulum and move through the cytomembrane system where they are modified

Overview Transcription Translation mRNA rRNAtRNA Mature mRNA transcripts ribosomal subunits mature tRNA

Gene Mutations Base-Pair Substitutions Base-Pair SubstitutionsInsertionsDeletions

Base-Pair Substitution original base triplet in a DNA strand During replication, proofreading enzymes make a substitution a base substitution within the triplet (red) original, unmutated sequence a gene mutation possible outcomes: or Figure Page 234

Frameshift Mutations Insertion Insertion Extra base added into gene region Extra base added into gene region Deletion Deletion Base removed from gene region Base removed from gene region Both shift the reading frame Both shift the reading frame Result in many wrong amino acids Result in many wrong amino acids

Frameshift Mutation mRNA parental DNA amino acids altered mRNA DNA with base insertion altered amino- acid sequence arginineglycinetyrosinetryptophanasparagine arginineglycineleucineglutamateleucine Figure Page 234

Mutation Rates Each gene has a characteristic mutation rate Each gene has a characteristic mutation rate Average mutation rate is approximately 1 in every 100,000 genes Average mutation rate is approximately 1 in every 100,000 genes Only mutations that arise in germ cells can be passed on to next generation Only mutations that arise in germ cells can be passed on to next generation

Mutagens Ionizing radiation (X rays) Ionizing radiation (X rays) Nonionizing radiation (UV) Nonionizing radiation (UV) Natural and synthetic chemicals Natural and synthetic chemicals