Ch 5 and16 A Close Look at the Hereditary Molecules Protein sequence-->programmed by genes Genes are made of DNA, a nucleic acid

LE 5-25 NUCLEUS DNA CYTOPLASM mRNA Ribosome Amino acids Synthesis of mRNA in the nucleus Movement of mRNA into cytoplasm via nuclear pore Synthesis of protein Polypeptide DNA RNA Protein Flow of genetic information

The Roles of Nucleic Acids Two types: –Deoxyribonucleic acid (DNA) –Ribonucleic acid (RNA) DNA provides directions for its own replication. DNA directs synthesis of messenger RNA (mRNA) mRNA controls protein synthesis. Protein synthesis occurs on ribosomes.

LE 5-26a 5 end 3 end Nucleoside Nitrogenous base Phosphate group Nucleotide Polynucleotide, or nucleic acid Pentose sugar Nucleic acid building block

Nucleic Acid Structure Monomers nucleotide (3 parts) 1. nitrogenous base 2. 5 C sugar 3. Phosphate Polymer polynucleotide or nucleic acid nucleoside

LE 5-26b Nitrogenous bases Pyrimidines Purines Pentose sugars Cytosine C Thymine (in DNA) T Uracil (in RNA) U Adenine A Guanine G Deoxyribose (in DNA) Nucleoside components Ribose (in RNA)

Important Nucleic Acid Distinctions Pyrimidines-one ring (T,U,C) Purines- two rings (G,A) DNA the sugar = deoxyribose NO 2’ OH (hydroxyl) Two kinds of bases RNA the sugar= ribose YES 2’ OH

Nucleotide Polymers Nucleotides (nt) connect through phosphodiester bond 5’ Phosphate--> 3’OH Creation of a sugar-phosphate backbone with bases as appendages. Sequence of bases along DNA or mRNA polymer unique for each gene.

LE end 3 end 5 end 3 end Space-filling modelPartial chemical structure Hydrogen bond Key features of DNA structure 0.34 nm 3.4 nm 1 nm Two DNA strands bind together through complementary base-pairing.

Francis Crick James Watson Structure of DNA double helix: published in 1953 Watson JD, Crick FHC Molecular structure of nucleic acids: a structure for deoxyribonucleic acids. Nature 171:738.

LE 16-6 Franklin’s X-ray diffraction photograph of DNA Rosalind Franklin Partly based on Franklin’s x-ray diffraction data

LE 16-8 Chargaff’s rules (1940s): Amount of A=T G=C

LE 16-UN298 Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data Watson & Crick: built model of DNA and tested possible combinations of bases Did model support Chargaff’s observations and Franklin’s x-ray diffraction data?

LE end 3 end 5 end 3 end Space-filling modelPartial chemical structure Hydrogen bond Key features of DNA structure 0.34 nm 3.4 nm 1 nm Antiparallel DNA strands Two DNA strands bind together through complementary base-pairing.

The DNA Double Helix Two polynucleotides (strands) base-paired together GC, AT (complementary base-pairing) Double helix Two sugar-phosphate backbones run in opposite 5´ to 3´ directions - antiparallel One DNA molecule includes many genes

Adenine (A) Thymine (T) Guanine (G) Cytosine (C) Sugar Complementary base pairs G=C 3 H-bonds A=T 2 H-bonds

Behavior of DNA Draw a 10 base pair double-stranded DNA (dsDNA) that is rich in AT. Draw a 10 base pair double-stranded DNA (dsDNA) that is rich in GC. If these were placed in a tube of boiling water what would happen? DNA would become single stranded (ssDNA) (denatured or melted). Which DNA would denature first. Why? AT rich fragment less stable 2 H-bonds/bp versus 3 H-bonds/bp

DNA Used as Evolutionary Ruler Linear sequences of DNA in chromosomes –passed from parents to offspring Two closely related species are more similar in DNA sequence than distantly related species Similarity of DNA sequence –Determines evolutionary relatedness

5’ GAACCTTCCAATTGATCT3’ 5’ GAACCAACCAATTAAACT3’5’ GAACCTTCGAATTGATCT3’ 1.Compare the human sequence to the frog and mouse. Which sequence is most similar to human? human mousefrog 2. Write in the complementary strand for each.

Earlier data suggested that DNA was hereditary material Model system: Drosophila melanogaster Investigator: Thomas Hunt Morgan (early 1900’s) Evidence: white eye phenotype associated with X-chromosome Model system: bacteria and viruses Investigators: Many Evidence: various

Evidence That DNA Can Transform Bacteria Evidence for genetic role of DNA (Frederick Griffith,1928) Heat-killed pathogenic “S” Streptococcus pneumoniae + “R”non-pathogenic bacterial strain Some living bacteria became pathogenic Transformation of “R’ to ‘S”, How could one determine pathogenicity experimentally?

LE 16-2 Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells Mouse dies Living S cells are found in blood sample Mouse healthy Mouse dies RESULTS

Oswald Avery, Maclyn McCarty, and Colin MacLeod (1944) Published results –Showed DNA from bacteria NOT protein--> caused transformation of “R” to “S” What molecule was responsible for conferring a new phenotype into an organism?

Alfred Hershey and Martha Chase (1952) –Used bacterial virus (bacteriophage) (T 2 ) to ask whether DNA or protein was hereditary material Independent confirmation

LE 16-3 Bacterial cell Phage head Tail Tail fiber DNA 100 nm

LE 16-4 Bacterial cell Phage DNA Radioactive protein Empty protein shell Phage DNA Radioactivity (phage protein) in liquid Batch 1: Sulfur ( 35 S) Radioactive DNA Centrifuge Pellet (bacterial cells and contents) Pellet Radioactivity (phage DNA) in pellet Centrifuge Batch 2: Phosphorus ( 32 P) Hershey & Chase labeling experiment Protein radiolabelled DNA radiolabelled Phage produced in and released from bacteria with radioactive DNA.

Hershey & Chase results -Suggest that DNA, not protein, is transferred to bacteria by phage. -DNA programs the reproduction of more phage. Contains important genetic instructions.

I’m a pretty cool molecule but I’ll still answer your questions.