DNA—the thread of life Biol 100 – K.Marr 1.Topics this lecture – DNA structure and Replication – Chapter 10 in Essential Biology by Campbell et al 2.Lab 7. Modeling DNA Structure, DNA Replication and Protein Synthesis Read the introduction carefully – This week: Part 1 (through page 9)—modeling DNA Structure and Replication – Next week: Part 2—modeling transcription and translation

Outline for Next few Lectures Chapter 10—Molecular Biology of the Gene – Cystic Fibrosis Case Study – Central Dogma of Biology – Structure of DNA – Replication of DNA – Protein Synthesis Transcription = Reading of DNA to make RNA Translation = Reading of mRNA by ribosomes to make protein Chapter 12—DNA Technology – Application of Gene Therapy and biotechnology to cystic fibrosis

Cystic fibrosis—a genetic disease 1.View GATTACA trailer 2.View Cystic Fibrosis Case Study Movie – lecture page of class website 3.Optional Reading – Cystic Fibrosis Foundation Website: – Welsh, M.J. and A.E. Smith. Cystic fibrosis. Scientific American, December 1995

Salty sweat due to altered salt secretion in sweat ducts Lung Pancreas Testis Infertilty in males due to clogged sex ducts Problems with digestion due to clogged duct from pancreas Mucus-clogged Airways; Severe Respiratory infections Symptoms of CF Cell lining ducts of the body

Cystic Fibrosis: autosomal recessive Most common lethal genetic disease – 1 in 2000 children is born with CF in U.S. – Untreated children die by age 5 – Ave. life expectancy: ~27 yrs – Special diet + daily dose of antibiotic prevent infection Carriers of CF gene: – Hispanics: 1 in 46 – African Americans: 1 in 63 – Asian Americans: 1 in 150 – Caucasian of European descent: 1 in 25 CF allele protects against the plague and many viruses

Cystic Fibrosis l A single faulty protein is connected to the symptoms l In 1989 the gene was mapped to chromosome #7

Our Goal To determine the connection between the symptoms associated with cystic fibrosis and DNA Let’s revisit the central dogma of biology…

Central Dogma of Biology Genes interacting with their environment determine the phenotype of an Organism

DNA Nucleus Transcription RNA Translation Protein Cytoplasm Central Dogma of Biology DNA specifies the synthesis of proteins in two stages 1.Transcription____ ________________ ________________ 2.Translation______ ________________ ________________ Let’s learn a bit about the structure of DNA

DNA is like a rope ladder twisted into a spiral Twist DNA Structure Consists of 2 strands joined together by weak hydrogen bonds Rungs of the ladder are hydrogen bonded N-bases View Animation of DNA & RNA Structure

Nucleotide: base + sugar + phosphate Note carbon numbers on sugar Nucleotides join to form a sugar- phosphate backbone DNA and RNA: Polymers of Nucleotides

Nitrogen Bases found in DNA & RNA Uracil replaces thymine in RNA

Phosphate group Nitrogenous base Sugar Nucleotide Polynucleotide Sugar-phosphate backbone Nitrogenous base (A,G,C, or T) Thymine (T) Phosphate group Sugar (deoxyribose) DNA nucleotide Representation of one Strand of DNA 3’ end 5’ end

DNA Structure Complementary pairing of bases A to T and G to C Note 5’ and 3’ ends of each strand

It’s in the genes... 1.What’s a gene? Sequence of DNA bases on a chromosome that determines the amino acid sequence of a protein 2.The kind of proteins an organism makes helps to determine it’s phenotype 3.Genes are... copied during __ S-phase of the cell cycle (DNA replication)_____ passed to offspring __during fertilization and when cells divide__ 4.Genes can change or mutate—how? View animation of DNA Replication  available at the lecture section of class website

Nucleus One DNA molecule before replication Parental strands Separated by Helicase Free nucleotides diffuse in and pair up with bases on the Separated strands— A with T, G with G DNA polymerase joins together the newly aligned nucleotides Parent strands conserved New strands formed DNA polymerase DNA Replication (simplified) After Replication: 2 Identical DNA molecules (sister chromatids) 5’ 3’ 5’ 3’

a.) Primer bindingb.) Synthesis begins Newly made strands Primer (5’ end) DNA polymerase and other enzymes Two strands of the parental DNA molecule DNA Replication: DNA polymerase can only add nucleotides to the 3’ end of another nucleotide (slide 1 of 2) 3’ end Replication fork moves Replication fork 5’ end

c.) Replication continuesd.) Replication complete Two identical daughter DNA molecules Replication fork moves DNA Replication (slide 1 of 2) This strand is synthesized continuously toward the fork This strand is made by discontinuous synthesis: Fragments are synthesized and then joined together

DNA replication Self-test Questions 1.When during the cell cycle does it occur? 2.What do we start with? 3.What do we end with? 4.Where in a cell does DNA replication occur? 5.What’s needed for DNA replication to occur? 6.What is the sequence of events? 7.Why is DNA replication said to be semi-conservative? 8.What does proofreading mean in terms of DNA replication? 9.What does the proofreading during DNA replication?

Thymine (T) AZT Part of a Thymine nucleotide How do nucleotide analogues work to stop DNA replication in cancer cells and HIV? The drug AZT, below, is effective at preventing the spread of HIV. How?

DNA can be damaged by ultraviolet light 1.Enzymes (e.g. DNA polymerase) can repair the damage. –Is the damage always repaired? Consequences? 2.Why does burnt skin peel? What gene is involved? 3.Role of Apoptosis? 4.Role of p53 gene? –Advantages of peeling? –Disadvantages?