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Chapter 12 and 13 Nucleic Acids, Protein Synthesis and Mutations Central Dogma DNA RNA Protein 1 Identifying the substance of Genes • Influential Scientists: • Griffith - Experimented with mice and bacteria that cause pneumonia and demonstrated TRANSFORMATION. - Concluded that some FACTOR (gene) was responsible for the change. • Avery - Followed up on Griffith’s experiment; wanted to know which molecule was important for transformation. - He then extracted the 4 macromolecules from these heat killed cells, all of which were considered to be possible candidates for the carriers of genetic information. - Treated each mixture with enzymes that destroyed the macromolecule and transformation still occurred. 2 - He concluded that DNA is the source of genetic information. Figure 12–2 Griffith’s Experiment Section 12-1 Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria (smooth colonies) Dies of pneumonia Lives Lives Control (no growth) Harmless bacteria (rough colonies) Dies of pneumonia Live, disease-causing bacteria (smooth colonies) 3 DNA • Influential Scientists continued: • Hershey and Chase- Studied viruses – non-living particles that can infect living cells. - Looked at bacteriophages – a virus that infects bacteria. - Supported the conclusion that genes were made of DNA. DNA is the source of genetic information Bacteriophage with phosphorus-32 in DNA Bacteriophage with sulfur-35 in protein coat Phage infects bacterium Phage infects bacterium Radioactivity inside bacterium No radioactivity inside bacterium 4 Where is DNA found? Inside the nucleus DNA is coiled into Chromosomes 5 Components of DNA • Nucleotide (monomer) – Deoxyribose sugar – Phosphate group – Nitrogen-containing base • Adenine (A) • Guanine (G) Purines • Cytosine (C) Pyrimidines • Thymine (T) 6 Components of DNA • The structure or shape of DNA = Double Helix = 2 strands – Watson and Crick (1953) – tried to assemble the structure. – Rosalind Franklin (1952) – used a technique known as x-ray diffraction to create a picture. • The x shape indicated DNA is twisted (helix) around two strands. 7 Components of DNA • Complementary Base Pairing – A↔T, G ↔C (Chargaff’s rule) – Connected by covalent hydrogen bonds DNA with Nucleotides 8 DNA Replication (duplication) • Takes place in the nucleus (during the S phase) • Result: 2 exact copies original DNA DNA Polymerase Helicase Replication fork 9 DNA Replication (duplication) • 1. Helicase unzips the double helix by breaking the hydrogen bonds forming a replication fork. • 2. DNA polymerase adds the complimentary base pairs to each separated strand. – DNA Polymerase also “proofreads” each new strand. Helicase DNA Polymerase Replication fork 10 DNA Replication, Accuracy & Repair • • • • • • • Original: A-T-T-C-C-G Complement: TAAGGC Original: GCTAAG • DNA polymerase Complement: proofreads & Original: CTACCA repairs1error/1Billion Complement: Original – Strand A: GACCTA – Strand B: 11 • Nucleotide Components – Ribose Sugar – Phosphate Group – Nitrogen Base • Adenine (A) • Guanine (G) • Cytosine (C) • Uracil (U): not T • Single Strand • 3 Types: – Messenger RNA (mRNA) – Transfer RNA (tRNA) – Ribosomal RNA (rRNA) of RNA 12 How to make RNA Step 1 = Transcription: DNA RNA Takes place in the nucleus 1. DNA unwinds. 2. RNA Polymerase binds to DNA promoter site (begin gene) Gene Begins RNA Polymerase 3. Add complementary RNA nucleotides (U↔A) 13 Transcription Continued 4. DNA termination sequence signals gene end RNA Polymerase 5. RNA Polymerase releases DNA & RNA RNA Strand DNA Rewinds 14 Transcription DNA makes RNA 15 3 Types of RNA 1. 3. Carries instructions from DNA to assemble amino acids into protein. The site where proteins get assembled from mRNA. 2. Carries the amino acids to the mRNA at the ribosome. 16 How to make Protein = Translation • Involves the decoding of mRNA and assembling a protein • Proteins = polymers = macromolecule – Monomer of protein = amino acid – Polypeptides = sequence of amino acids • Genetic code is read 3 letters at a time. – Codon: every 3 base pairs in mRNA = an amino acid • START Codon: starts translation- 1 codon only AUG • STOP Codon: stops translation- 3 codons UAA, UAG, UGA – Universal Codon -Amino Acid Code: p. 367 17 mRNA Codon & Codon Chart • AUG = – Methionine or start codon • AAC = _________ Amino Acids 18 19 How to make Protein = Translation • tRNA – In cytosol – Binds specific amino acid to mRNA – Anticodon: • complement to mRNA codons 20 Translation: mRNA Protein 1. mRNA leaves nucleus 2. Ribosome attaches to mRNA start codon 3. mRNA codon pairs with tRNA anticodon delivering amino acid. 4. Peptide bond forms between amino acids 21 Translation: mRNA Protein 5. mRNA stop codon signals end of translation. The ribosome releases the newly formed polypeptide. 6. mRNA released & polypeptide complete 22 Translation Diagram Polypeptide Chain Peptide Bond Nucleus Amino Acid tRNA Anticodon mRNA Codon Ribosome 23 Overview DNA RNA Protein Transcription Translation 24 Mutations • Mutations – are heritable changes in genetic info. • Occurs in only 2 types of cells – Sex-cell (germ-cell) mutations: gametes affect offspring – Somatic mutations: body cells affect individual • 2 categories of mutations – Gene mutations produce change in a single gene – Chromosomal mutations produce change in a whole chromosome. 25 Gene Mutations A.K.A. Point Mutations (3 types) 1. Substitution 1 nitrogen base gets substituted by another nitrogen base; this results in a new codon – Sickle Cell Anemia: substitute A for T 26 Gene Mutations (con’t) Deletion 2. Nucleotide deletions & insertions – One base is inserted or removed from the sequence. - Causes Frame-shift mutations – Changes amino acid sequence Insertion Deletion 27 Chromosomal Mutations (5 types) • Deletion: lose portion • Duplication: gain extra portion • Inversion: segment reverses • Translocation: transfer segment to non-homologous • Nondisjunction: gamete gets extra or less chromosome (Down Syndrome- Trisomy 21) 28 Chromosome Mutations Diagrams 29 Genetic Traits & Disorders • Disorders due to nondisjunction – Nondisjunction: gametes have 1 more or less chromosome (pairs don’t segregate) – Monosomy: 45 chromosomes • Turner’s syndrome: XO – Trisomy: 47 chromosomes • Down Syndrome: trisomy-21 • Kleinfelter’s syndrome: XXY • Patau syndrome: trisomy-13 • Edward’s syndrome: trisomy-18 30