I. Early Discoveries • DNA only has 4 building blocks. 1. Protein (20 monomers) seemed more likely. B. Frederick Griffith – 1928 1. Dead pathogenic bacteria pass something to live harmless ones, making them deadly.
Virus C. Hershey & Chase-1952 1. Used radioactive atoms to label viruses 2. Sulfer-35 to label protein. 3. Phosphorous-32 for DNA 4. P32 ended up in bacteria, so DNA was passed on.
D. Erwin Chargaff – • The amount of T matches amount of A. • G matches C E. Rosalind Franklin and M. Wilkins • X-ray crystal photos suggest DNA is a double helix.
II. DNA’s properties • A. 4 Nitrogen Bases: Adenine, Guanine, Cytosine, Thymine • 1. Bonding is always: A---T G---C 2. Complementary bases
B. Nucleotide – 3 parts phosphate Nitrogen base sugar #5 Carbon #3 Carbon
C. DNA Base Pairing 1. Hydrogen bonding holds the 2 strands together a. Backbone-alternating Sugar and Phosphate b. Anti-Parallel – Strands run opposite. c. Bases with 2 rings - Purines d. Bases with 1 ring - Pyrimidines
2.0 nm 3.4 D. Size • One complete turn of double helix spans 10 base pairs. • Angle between consecutive bases? • 36 degrees 3. One turn is 3.4 nm • Distance between bases? • .34 nm 4. Width: 2.0 nm
MOVIE • -QUIZ - Complementary DNA strand? • ATCGCCGTTAGTATA • TAGCGGCAATCATAT
Watson and Crick Lecture 2. DNA REPLICATION
DNA Replication is Semi-conservative. • Each original strand serves as a template for making the new strands. • 6 billion base pairs replicated in 3-4 hours. New DNA Strands
B. Case Study - HIV drug AZT • HIV virus reproduces in and kills white blood cells. • WBC count gets low. Allows infections • AZT – Blocks viral DNA replication.
C. Steps • The 2 strands are separated by • Helicase enzyme. • Open section is a “replication bubble”. • 2. DNA Polymerase builds a new strand by reading original base and inserting complementary base.
D. Nucleotides can only be added to the 3’ carbon of the previous one. • DNA grows 5’ to 3’. • Leading Strand- grows toward replication fork. • Lagging Strand – Grows away from fork. • Builds in short pieces called Okazaki fragments Movie
E. AZT Cont. • AZT molecule has similar shape as Thymine. • 3’ carbon has -N3, not -OH. • Viruses insert AZT instead of thymine. • Next base can’t attach to N3. • Strand growth stops. • New virus can’t be made.
AZT 2. Side effects? a. Human machinery for copying DNA works similarly to virus. • Dividing human cells insert AZT in DNA, can’t finish copying, and die. • What’s worse, the disease or the treatment?
DNA Lecture 3 – Transcription • The process of copying the recipe in genes to RNA.
II. Case Study –Lactose Intolerance A. Many people can’t make lactase enzyme. • Can’t digest lactose in milk. • Causes gas from bacteria.
Transcription- Making Messenger RNA • RNA Polymerase – • a. Opens helix and makes mRNA strand from DNA template.
B. mRNA editing • Introns are cut out. • Exons are fused together. • Contains the message that will leave the nucleus. What is the mRNA? DNA: ATCGCCGTTA RNA: UAGCGGCAAU
C. Each group of 3 bases in mRNA is a codon. 1. Each codes for a specificamino acid. a. 3000 bases = ______ codons • 1000 b. Codes for _____ amino acids. • 1000
D. Lactose Intolerance cont. 1. 75% of adults worldwide show some LI. 2. Ability of adults to digest lactose results from a recent mutation.
E. The Lactose Operon A set of genes that are regulated together • A repressor protein blocks RNA Polymerase from transcribing the 3 lactase genes. • Lactose attaches to the repressor, makes it leave. • Allows transcription. • When lactose is used up, repressor re-attaches. a. Enzyme is made ONLY WHEN ITS NEEDED.
F. The Codon Table 1. Redundancy: multiple codons for same amino acid. 2. Start Codon- AUG • first amino acid is always methionine. 3. Stop Codons - no amino acid, stops protein growth. Find the amino acids coded for by these sequences: • 1.mRNA: AUGUGGCUUAAA 2. DNA: AAATACCGGACT • (start)met-trp-leu-lys
How is mRNA Read? • Transfer RNA • Has a 3-base “anticodon.” • Other end has an amino acid attached. B. tRNA’s anticodon must match mRNA codon. • Correct amino acid is delivered to build the protein. CGU GCA mRNA
Ribosome – The “Matchmaker” A. Holds mRNA so tRNA can pair with it.
Steps of Translation • tRNA carrying MET binds to the start codon • At the P-site.
Peptide Bond Step 2. Next tRNA fills the A-site. 3. A peptide bond forms
4. Ribosome shifts, A-site now empty. • Next tRNA enters. 6. Continues until a “Stop” codon. Video
Mutations “The fat cat ate the wee rat” • A permanent change in the DNA. B. Types • Substitution – Changes one base, one codon. • Change an “e” to an “a”. 2. Insertion / deletion – “Frameshift” • A base is added or removed. Causes whole new set of codons after that point. • Remove “t” in cat and shift subsequent letters left one space • Causes premature stop. • Inversion – Section of DNA flips 180o. • Read the sentence backwards