Fig 16 8 Complementary Base Pairing Showing hydrogen

Fig. 16 -8 Complementary Base Pairing Showing hydrogen bonding Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Fig. 16 -UN 2 G C A T G Sugar-phosphate backbone “sides of the ladder” C A C G T C Nitrogenous bases “rungs of the ladder” G Hydrogen bond T A

Fig. 16 -7 a 5 end Hydrogen bond 3 end 1 nm 3. 4 nm 3 end 0. 34 nm (a) Key features of DNA structure Strands of DNA – run opposite each other; this is called antiparallel. 5 end

Fig. 16 -5 Sugar–phosphate backbone 5 end Nitrogenous bases Carbon 1 – bonds to nitrogen base Purines • Adenine • Guanine Carbon 3 – bonds to next nucleotide Carbon 5 – bonds to phosphate group Thymine (T) Adenine (A) Pur. As. Gold Pyrimidines • Cytosine • Thymine • Uracil Py. CUT Cytosine (C) DNA nucleotide Phosphate Sugar (deoxyribose) 3 end Guanine (G)

Fig. 16 -UN 1 Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data

• At first, Watson and Crick thought the bases paired like with like (A with A, and so on), but such pairings did not result in a uniform width • Instead, pairing a purine with a pyrimidine resulted in a uniform width consistent with the X -ray Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

• Watson and Crick reasoned that the pairing was more specific, dictated by the base structures • They determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C) • The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T, and the amount of G = C Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Concept 16. 2: Many proteins work together in DNA replication and repair • The relationship between structure and function is manifest in the double helix • Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 16 -9 -3 A T A T C G C G T A T A T G C G C (a) Parent molecule (b) Separation of strands (c) “Daughter” DNA molecules, each consisting of one parental strand one new strand Semiconservative

The Basic Principle: Base Pairing to a Template Strand • Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication • In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

to w ? ho rt w cha no on u k od yo is c Do e th Us Third m. RNA base (3�end of codon) First m. RNA base (5�end of codon) Fig. 17 -5 Second m. RNA base

Enzymes involved in DNA Replication & Transcription Enzyme Function Helicase “molecular zipper” – unwinds double helix; breaks hydrogen bonds that holds base pairs together Primase Creates an RNA primer so DNA polymerase will know where to start in order to manufacture a new DNA strand. DNA polymerase Using a parent DNA strand, adds freefloating nucleotides (A, T, G, & C’s) covalently to the new strand being constructed. ligase “molecular glue” – joins fragments of the New DNA strand together RNA polymerase (used in transcription) Uses one strand of DNA as a template to construct m. RNA – adds free-floating nucleotide Exonuclease Removes RNA primers from the DNA strand after replication has occurred, so DNA polymerase can come in and fill in the gaps with DNA nucleotides to finish the process. Fixes mistakes on DNA molecule. Also can fix mutations that occur during DNA replication.

Transcription & Translation refer to diagram drawn on board also watch animations: DNAi. org Khanacademy. org Crash Course (youtube)

DNA – A Historical Perspective 1831 -1836 – Charles Darwin, British naturalist - famous voyage on HMS Beagle. 1859 – published famous book on the Origin of Species which reveals the idea of Evolution by means of natural selection. 1858 – Alfred Wallace, – British biologist conducting field work in Malaysia. Sends a short essay to Darwin with similar theory of evolution. 1865 – Gregor Mendel, Austrian monk – “Father of Heredity” 1869 – Johann Miescher (Swiss biochemist) – isolates DNA from WBC 1928 – Frederick Griffith – British Bacteriologist – discovers transformational factor 1944 – Oswald Avery et al. - Canadian-born American physician – shows that the transformational factor was not a protein but DNA 1947 – Erwin Chargaff – Austrian biochemist – developed Chargaff’s ratios 1952 – Alfred Hershey & Martha Chase – provide conclusive evidence that DNA is the transformational factor 1952 – Rosalind Franklin & Maurice Wilkins – use x-ray diffraction to analyze DNA 1953 – James Watson & Francis Crick construct double helix model of DNA

Johannes Friedrich Miescher 1844 -1895 In 1869, first to isolate a substance he called nuclein from the nuclei of leucocytes or WBC Collected these from pus he obtained from bandages at nearby hospitals. He found that nuclein contained phosphorus and nitrogen, but not sulfur

Frederick Griffith 1871 - 1941 What is the transformational factor? ? ? Is it DNA or Protein? ? ? Griffith’s research, working with two strains of a bacterium, one pathogenic and one harmless, addresses this vital question In 1941, Griffith was killed at work in his London laboratory as a result of an air raid in the London Blitz.

DNA – A Historical Perspective Griffith and Transformation 1928 – British pathologist was researching How certain types of bacteria produced pneumonia He isolated 2 different strains: R which was harmless and S - virulent

Live S-strain kills mouse

Injection of Rough Colonies ( R) Results in Live Mice

Heat-killed Smooth colonies (S) Result in Live Mice

Heat-Killed S + Live R = Dead Mice

Fig. 16 -2 Mixture of heat-killed Living S cells Living R cells Heat-killed S cells and (control) S cells (control) living R cells EXPERIMENT RESULTS Mouse dies Mouse healthy Mouse dies Living S cells

Oswald Avery and DNA (1944) Working along with Colin Macleod & Maclyn Mc. Carty Repeated Griffith’s work with modifications Which molecule in the heat-killed was the transformational factor? The components of the Ground up S were isolated, each mixed with R and injected into mice

If the Heat-Killed S-strain’s DNA is destroyed with DNAase then R-strain can not be converted to live S-strain. The gene to produce the capsule has been destroyed.

In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T 2 To determine the source of genetic material in the phage, they designed an experiment showing that only one of the two components of T 2 (DNA or protein) enters an E. coli cell during infection They concluded that the injected DNA of the phage provides the genetic information Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 16 -3 Phage head Tail sheath Tail fiber Bacterial cell 100 nm DNA

Fig. 16 -4 -3 EXPERIMENT Phage Empty protein Radioactive shell protein Radioactivity (phage protein) in liquid Bacterial cell Batch 1: radioactive sulfur (35 S) DNA Phage DNA Centrifuge Pellet (bacterial cells and contents) Radioactive DNA Batch 2: radioactive phosphorus ( 32 P) Centrifuge Pellet Radioactivity (phage DNA) in pellet

Fig. 16 -6 (a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA

Maurice Wilkins 1916 -2004 Kings College London

Erwin Chargaff (1905 -2002) and “Chargaff’s Rules” The bases were not present in equal quantities They varied from organism to organism. No matter where DNA came from — yeast, people, or salmon — the number of adenine bases always equaled the number of thymine bases and the number of guanine always equaled the number of cytosine bases. He published a review of his experiments in 1950, calling the ratios — which came to be known as Chargaff’s Rules

Chargaff’s rules state that in any species there is an equal number of A and T bases, and an equal number of G and C bases Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings