DNA Deoxyribose nucleic acid type of nucleic acid – What is the other type of nucleic acid? RNA DNA function – to hold genetic code – Genetic code = genetic information/instructions for making proteins DNA is found in nucleus of eukaryotic cells Found in nucleoid region in prokaryotes
What is DNA made of? DNA is a macromolecule – Made up of nucleotides – Covalently and hydrogen bonded together Double stranded – Helix – “Spiral”
What is a nucleotide? Molecule made of – Deoxyribose sugar – A phosphate group – A nitrogenous base
The Short History of DNA and Genetics (Part 1) From 1866-1953
Searching for Genetic Material Gregor Mendel (1866): –discovered that inherited traits are determined by discrete units, or 'genes,’ - passed on from the parents. Thomas Hunt Morgan (1910): – Discovered genes are located (linked) on chromosomes
Searching for Genetic Material Fredrick Griffith (1928): – Studied effects of virulent (virus-causing) bacteria vs. nonvirulent bacteria injected into mice – Used transformation: Inserted foreign DNA and changed protein/ trait – believed that the transforming agent was an inheritance molecule.
Griffith's Transformation Experiment Used the Pneumococcus bacteria –Include2 types: a virulent S strain with a Smooth coat –ki ll s mice a non-virulent R Rough strain –does not kill mice. Heat destroys the harmfulness of S strain When heated S is mixed with live R and injected into mice, the mouse dies. WHY?
Searching for Genetic Material http://brookings.k12.sd.us/biology/ch12DNARNA/Chapter%2012A.mpg
Searching for Genetic Material Oswald Avery, Colin MacLeod, & Maclyn McCarty (1944): Reported that “transforming agent” in Griffith's experiment was DNA. Also u sed the Pneumococcus bacteria and test tubes (NOT mice)
Discovering the Structure of DNA Edwin Chargaff (1950) Discovered a 1:1 ratio of adenine to thymine and guanine to cytosine in DNA samples from a variety of organisms. Noticed that: # of Adenine = # of Thymine # of Cytosine = # of Guanine “Chargaff’s Rule”
Chargaff's Rule (Data) Relative Proportions (%) of Bases in DNA ORGANISM ATGC Human30.929.419.919.8 Chicken28.829.220.521.5 Grasshopper29.3 20.520.7 Sea Urchin32.832.117.717.3 Wheat27.327.122.722.8 Yeast31.332.918.717.1 E. coli24.723.626.025.7
Discovering the structure of DNA Chargaff movie and Building Blocks movie http://www.hhmi.org/biointeractive/dna /animations.html Chargaff’s Rules A = T C = G C and G are held more tightly together because they are connected by three hydrogen bonds, whereas A and T are held by only two.
Discovering the structure of DNA Maurice Wilkins (1952) Studied DNA using x-ray crystallography with another scientist named Rosalind Franklin He showed Franklin’s x-ray photograph without Franklin’s consent to Watson and Crick, which helped them discover DNA’s structure. Awarded the 1962 Nobel Prize for Physiology or Medicine with Watson and Crick
Discovering the structure of DNA Rosalind Franklin (1952) Obtained sharp X-ray diffraction photographs of DNA (Photo 51) Watson and Crick used her data revealed its helical shape Watson and Crick went on to win Nobel Prize (1962) for their DNA model Photo 51
X-rays passing through a helix diffract at angles perpendicular to helix making an "X" pattern, which favors an equal diameter "helix".
She finally gets credit Rosalind Franklin University of Medicine and Science, located on Green Bay Road in North Chicago, Illinois
How was the structure of DNA discovered? 1953 – Watson and Crick – Wilkins shows Watson and Crick the x-ray pictures from Franklin This information gave Watson & Crick the evidence to conclude DNA has a helical shape – Made model of DNA which was made up of two chains of nucleotides
Discovering the structure of DNA James Watson & Francis Crick (1953) Discovered double helix structure Solved the three-dimensional structure of the DNA molecule Watson Constructing Bair Pairs movie http://www.hhmi.org/biointeractive/dna/animations.html
What is the Double Helix? Shape of DNA Looks like a twisted ladder 2 coils are twisted around each other Double means 2 Helix means coil
DNA - basics Deoxyribonucleic Acid Stores and transmits genetic info Tells the cells which proteins to make and when to make them Made up of nucleotides – Phosphate group – Sugar – Nitrogen bases Double helix structure
The Structure of DNA Made out of nucleotides Includes a phosphate group, nitrogenous base and 5-carbon pentose sugar Nucleotide Structure 1 “link” in a DNA chain
A Polynucleotide MANY nucleotides (“links”) bonded together Nucleotide Structure DNA has a overall negative charge b/c of the PO 4 -3 (phosphate group)
The Structure of DNA Backbone = alternating P’s and sugar Held together by COVALENT bonds (strong) Inside of DNA molecule = nitrogen base pairs Held together by HYDROGEN bonds (weaker) Backbone
Phosphodiester Bond – The covalent that holds together the backbone – Found between P & deoxyribose sugar – STRONG!!!
DNA is antiparallel Antiparallel means that the 1 st strand runs in a 5’ 3’ direction and the 2 nd 3’ 5’ direction – THEY RUN IN OPPOSITE or ANTIPARALLEL DIRECTIONS P end is 5’ end (think: “fa” sound) -OH on deoxyribose sugar is 3’ end – 5’ and 3’ refers to the carbon # on the pentose sugar that P or OH is attached to
Nitrogen Bases (2 types) Purines (small word, big base) – Adenine – Guanine P y rimidines – (big word, small base) – C y tosine – Th y mine Chargaff’s rules – A=T, C=G – Hydrogen Bonds – Hydrogen Bonds attractions between the stacked pairs; WEAK bonds
Why Does a Purine Always Bind with A Pyrimidine?
DNA Double Helix http://www.sumanasinc.com/webc ontent/animations/content/DNA_st ructure.html http://www.sumanasinc.com/webc ontent/animations/content/DNA_st ructure.html Watson & Crick said that… – strands are complementary; nucleotides line up on template according to base pair rules (Chargaff’s rules) A to T and C to G LET’S PRACTICE… Template strand: 3’AATCGCTATAC5’ Complementary strand: 5’TTAGCGATATG3’