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DNA, RNA, & Protein Synthesis Ch.10 (10-1) Discovery of DNA • Griffith – Transformation: transfer of genetic material from 1 cell to another • Avery – Concluded DNA is responsible for transformation in bacteria • Hershey-Chase – Used bacteriophages to conclude that DNA is the hereditary molecule in viruses Griffith & Avery Hershey-Chase (10-2) DNA • Organic cmpd • Made up of repeating subunits (nucleotides) • 2 long chains Structure of DNA • 3 parts: 1. Deoxyribose – sugar molecule 2. Phosphate group – PO433. Nitrogen-containing base – has N atom 4 N-Containing Bases 1. Adenine (A) 2. Guanine (G) 3. Cytosine (C) 4. Thymine (T) • Purines: 2 rings of C & N atoms – A&G • Pyrimidines: 1 ring of C & N atoms – C&T Double Helix • Watson & Crick (1953) suggested model • Used Franklin & Wilkins’ x-ray photograph “Backbone” • Sugar & phosphate covalently bonded • Bases face center & are perpendicular to backbone • H-bonds hold strands together Complementary Base Pairing • 2 rules: 1. C pairs w/ G 2. A pairs w/ T • Nucleotide sequence in 1 chain is complement of other chain (10-3) DNA Replication • Replication fork: area where chains separate • Helicase: enzyme that breaks H-bonds b/w bases causing chains to separate – Each chain serves as a template for a new chain DNA Polymerase • Enzyme that binds to separated strands of DNA & assembles each strand’s complement • Old: ATTCCG • New: TAAGGC Accuracy & Repair • High accuracy – Proofreading – Repair enzymes • Mutation: change in nucleotide sequence – DNA can also be damaged by chemicals & UV light (10-4) RNA • Ribonucleic acid • 3 types: m, t, r RNA Structure • • • • Repeating nucleotides Single-stranded Ribose: sugar molecule Uracil replaces thymine – U pairs w/ A Messenger (mRNA) • • Single, uncoiled chain Carries genetic info from DNA in nucleus to ribosomes in cytosol Transfer (tRNA) • • • Single chain Nucleotides folded into hairpin shape Binds to specific amino acids (aa) Ribosomal (rRNA) • • • Most abundant form Globular Make up ribosomes Transcription • Genetic info is copied from DNA to mRNA (transcript) • Occurs in nucleus • Methylation: regulation of gene expression & can stop transcription – Leads to cell specialization Steps of Transcription 1. RNA polymerase binds to promoter of a specific gene 2. Complementary copy of 1 strand made using RNA nucleotides (A w/ U, C w/ G) 3. Polymerase reaches termination signal & transcription stops Genetic Code • Correlation b/w nucleotide & aa’s – 20 different aa to make proteins (polypeptide) • Used by most organisms to translate mRNA transcripts into proteins Codon • 3 mRNA bases = 1 codon – Codes for proteins • Start codon: signal ribosome to start translating mRNA – AUG • Stop codon: cause ribosome to stop translating mRNA – UAA, UAG, UGA Translation (Protein Synthesis) • Assembling proteins from info encoded in mRNA • Anticodon: tRNA segment complementary to mRNA codon Steps of Translation 1. Codon (mRNA) paired w/ anticodon (tRNA) 2. tRNA adds specific aa to the growing polypeptide chain Ribosomes • Free in cytosol & some attached to ER • Binding sites for translation: – Holds mRNA transcript – Holds tRNA Protein Assembly 1. Ribosome attaches to start codon on mRNA transcript • Pairs w/ tRNA anticodon 2. Ribosomes move along mRNA • Aa continue to attach as anticodons paired 3. Ribosome reaches a stop codon • mRNA is released & protein is complete