Lecture%2015

Lecture%2015 - BILD1 The Cell Prof. Lisa M. Boulanger...

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1 03/06/07 BILD1 - Lecture 15 1 BILD1 The Cell Prof. Lisa M. Boulanger 03/06/07 BILD1 - Lecture 15 2 Supplemental reading for today: Sense and Antisense (posted) Problem Set 5 posted Discussed in Sections this week Study guide for Final posted this weekend 03/06/07 BILD1 - Lecture 15 3 Evidence that DNA is genetic blueprint Behavior of chromosomes during mitosis Transformation of bacteria by pathogenic DNA Viral DNA enters bacteria Chargaff: diversity among species in DNA sequences Structure of DNA Franklin X ray crystallography Watson and Crick double helix Monomers of nucleotides, linked by condensation / dehydration reaction A-T 2 hydrogen bonds, C-G 3 hydrogen bonds Highlights from previous lecture: DNA 100 nm 03/06/07 BILD1 - Lecture 15 4 Highlights from previous lecture: DNA replication Conservative, semiconservative, or dispersive? Meselson and Stahl: semiconservative Initiation, lateral expansion, fusion; Origin of replication, replication fork Replication machinery includes: Helicase, topoisomerase, SSBPs, DNA pol III, Okazaki fragments, DNA ligase, primase, DNA pol I 03/06/07 BILD1 - Lecture 15 5 Review: DNA Replication Leading strand (moves toward the replication fork) DNA replicated only in 5’ 3’ direction Polymerization only takes place at the 3’ end (3’OH) Lagging strand (moves away the replication fork) RNA primer 03/06/07 BILD1 - Lecture 15 6 Helicase SSBP DNA Replication: Overview
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2 03/06/07 BILD1 - Lecture 15 7 Proofreading and Repairing DNA • DNA polymerases proofread newly made DNA – Replacing any incorrect nucleotides • In mismatch repair of DNA – Repair enzymes correct errors in base pairing 03/06/07 BILD1 - Lecture 15 8 Nuclease DNA polymerase DNA ligase Thymine dimer distorts DNA 1 Nuclease cuts damaged DNA (removed) 2 Repair synthesis by DNA polymerase fills in missing nucleotides 3 DNA ligase seals free end of the new DNA to the old DNA, making the strand complete 4 • In nucleotide excision repair – Enzymes cut out and replace damaged stretches of DNA 03/06/07 BILD1 - Lecture 15 9 • The ends of eukaryotic chromosomal DNA – Get shorter with each round of replication 03/06/07 BILD1 - Lecture 15 10 • Eukaryotic chromosomal DNA molecules – Have at their ends nucleotide sequences, called telomeres, that postpone the erosion of genes near the ends of DNA molecules 1 μm 03/06/07 BILD1 - Lecture 15 11 • If the chromosomes of germ cells became shorter in every cell cycle – Essential genes would eventually be missing from the gametes they produce • An enzyme called telomerase – Catalyzes the lengthening of telomeres in germ cells ~2500 base pairs at the end of DNA is a repeat TTAGGG AATCCC – Telomerase is a protein with a built-in RNA template » AAUCCCAAU » Adds back telomere ends 03/06/07 BILD1 - Lecture 15 12 Growing polypeptides Completed polypeptide Incoming ribosomal subunits End of mRNA (3 end) Polyribosome Ribosomes mRNA 0.1 μm From DNA to TRANSCRIPTION AND TRANSLATION!
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3 03/06/07 BILD1 - Lecture 15 13
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Lecture%2015 - BILD1 The Cell Prof. Lisa M. Boulanger...

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