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Chapter 17. From Gene to Protein. Basic Principles of Transcription and Translation. Transcription = DNA mRNA ( mRNA = messenger RNA ) Translation = mRNA polypeptide Occurs on ribosomes. Basic Principles of Transcription and Translation. Transcription = DNA mRNA
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Chapter 17 From Gene to Protein
Basic Principles of Transcription and Translation • Transcription = DNA mRNA (mRNA =messenger RNA) • Translation = mRNApolypeptide • Occurs on ribosomes
Basic Principles of Transcription and Translation • Transcription = DNA mRNA (mRNA =messenger RNA) • Translation = mRNApolypeptide • Occurs on ribosomes DNA mRNApolypeptide
Prokaryotes • Transcription and translation occur together Figure 17.3a
Eukaryotes- • Transcription occurs in nucleus
Eukaryotes- • RNA transcripts are modified before becoming true mRNA
Eukaryotes- • Translation occurs in cytoplasm
Cellular chain of command • DNARNAamino acid (protein)
Cracking the Code • Codon = 1. Translated into an amino acid 2. Serves as a translational start/stop signal
DNA sequences in gene: • CCTCAGAGTGTG • TACGTTGCGCCC TRANSCRIPTION • RNA sequence = ? TRANSLATION • Amino acid sequence = ?
Codons must be read in the correct reading frame • Ex: “The red dog ate the cat” • Change reading frame “her edd oga tet hec at”
Concept 17.2: Transcription • DNARNA: a closer look
RNA synthesis Catalyzed by RNA polymerase 1. Pries the DNA strands apart 2. Adds and Hooks together the RNA nucleotides
Synthesis of an RNA Transcript • 3 stages of transcription: 1. Initiation 2. Elongation 3. Termination
3 steps of transcription • 1. Initiation –more specific in Eukaryotes • 2. Elongation • 3. Termination
Initiation of Transcription Prokaryote Vs. Eukaryote Promoters: Prok. = RNA Pol Bind to promoter sequence Euk. = Transcription factors bind first to TATA box then RNA pol II binds
Concept 17.4 • Translation = RNA directed synthesis of a polypeptide • mRNApolypeptide
Translation • Takes place in the cytoplasm • Ribosome attaches to an mRNA • Codon mRNA messagepolypeptide by tRNA
Amino acid attachment site tRNA- transfer RNA: 1. specific amino acid attachment site 2. base triplet called an anticodon on one end ANTI-CODON
Amino acid? tRNA- transfer RNA: 1. specific amino acid attachment site 2. base triplet called an anticodon on one end Anti-Codon? GGA
Glycine tRNA- transfer RNA: 1. specific amino acid attachment site 2. base triplet called an anticodon on one end CCU GGA
Ribosomes have 2 subunits (small + large) • Hold the tRNA and mRNA close together during translation tRNA binding sites Large Subunit P A E P A mRNA binding site Small Subunit
Building a Polypeptide • We can divide translation into three stages • Initiation • Elongation • Termination
Initiation mRNA, tRNA, and ribosome subunits assemble
Elongation: Step 2- peptide bond formation 2 1 2 1 1 2
Elongation: 2 1 1 2
Elongation: Step 3- translocation 3 2 2 1 1 2 1 2
Termination of Translation: Step 3 • Ribosome reaches a stop codon in the mRNA Release Factor
Concept 17.7 • Mutations- changes in the genetic material of a cell • Point mutations • changes in just one base pair of a gene
Normal Figure 17.23
Normal Point Mutation Figure 17.23
Types of Point Mutations • Point mutations • Base-pair substitutions • Base-pair insertions or deletions
Substitutions • A base-pair substitution • Can cause missense or nonsense Figure 17.24