Transcript Chapter 14
From DNA to Proteins Chapter 14 Marvelous Mussel Adhesive Mussel binds itself to rocks with threads coated with the protein bysuss Gene for bysuss has been put into yeast Yeast synthesize the protein based on the instructions in the mussel DNA Steps from DNA to Proteins Same two steps produce all proteins: 1) DNA is transcribed to form RNA Occurs in the nucleus RNA moves into cytoplasm 2) RNA is translated to form polypeptide chains, which fold to form proteins Three Classes of RNAs Messenger RNA Ribosomal RNA Carries protein-building instruction Major component of ribosomes Transfer RNA Delivers amino acids to ribosomes A Nucleotide Subunit of RNA uracil (base) phosphate group sugar (ribose) Figure 14.2 Page 228 Base Pairing during Transcription DNA G C A T RNA G C A U DNA C G T A DNA C G T A base pairing in DNA replication base pairing in transcription Transcription & DNA Replication Like DNA replication Nucleotides added in 5’ to 3’ direction Unlike DNA replication Only small stretch is template RNA polymerase catalyzes nucleotide addition Product is a single strand of RNA Promoter 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 Gene Transcription transcribed DNA winds up again DNA to be transcribed unwinds mRNA transcript RNA polymerase Figure 14.4c Page 229 Adding Nucleotides 5’ growing RNA transcript 3’ 5’ 3’ direction of transcription Figure 14.4d Page 229 Genetic Code Set of 64 base triplets Codons 61 specify amino acids 3 stop translation Figure 14.7 Page 230 tRNA Structure codon in mRNA anticodon amino-acid attachment site amino acid OH Figure 14.8 Page 231 Ribosomes tunnel small ribosomal subunit large ribosomal subunit intact ribosome Figure 14.9b,c Page 231 Three Stages of Translation Initiation Elongation Termination Initiation Initiator tRNA binds to small ribosomal subunit Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG “start” codon Large ribosomal subunit joins complex Fig. 14.10a-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 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 Elongation Fig. 14.10e-g Page 233 Termination Stop codon into place No tRNA with anticodon Release factors bind to the ribosome mRNA and polypeptide are released mRNA new polypeptide chain Fig. 14.10j-k Page 233 What Happens to the New Polypeptides? Some just enter the cytoplasm Many enter the endoplasmic reticulum and move through the cytomembrane system where they are modified Transcription Overview mRNA Mature mRNA transcripts Translation rRNA ribosomal subunits tRNA mature tRNA Gene Mutations Base-Pair Substitutions Insertions Deletions Base-Pair Substitution a base substitution within the triplet (red) original base triplet in a DNA strand During replication, proofreading enzymes make a substitution possible outcomes: or original, unmutated sequence a gene mutation Figure 14.11 Page 234 Frameshift Mutations Insertion Extra base added into gene region Deletion Base removed from gene region Both shift the reading frame Result in many wrong amino acids Frameshift Mutation mRNA parental DNA arginine glycine tyrosine tryptophan asparagine amino acids altered mRNA arginine glycine leucine leucine glutamate DNA with base insertion altered aminoacid sequence Figure 14.12 Page 234 Mutation Rates Each gene has a characteristic mutation rate 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 Mutagens Ionizing radiation (X rays) Nonionizing radiation (UV) Natural and synthetic chemicals