The DNA Revolution • 1940s-1960s • Griffith & Avery—DNA transformed pneumococcus bacteria. • Encouraged the study of prokaryotic chromosomes. • Hershey and Chase—Bacteriophage experiment. DNA from viruses is injected to host bacteria cells.
The Search for the Structure of the DNA Molecule • 1951—Rosalind Franklin—X-ray crystallography • Chargaff—Chargaff’s rules. Ratio of nitrogenous bases in DNA. Complimentary bases. • Watson & Crick--1953
Nucleotides Sugar—Deoxyribose Phosphate Group Nitrogenous Bases Adenine & Thymine are complementary. Cytosine and Guanine are complimentary. Purines—Adenine & Guanine Pyrimidines—Cytosine & Thymine 5’ End—Phosphate side 3’ End—Other side Watson & Crick Model of DNA
DNA is composed of 2 chains of nucleotides that form a double helix shape. The two strands are antiparallel. The backbone of the DNA molecule is composed of alternating phosphate groups and sugars. The complimentary nitrogenous bases form hydrogen bonds between the strands. A is complimentary to T and G is complimentary to C. Watson & Crick Model
DNA • Functions • 1. Storage of genetic information • 2. Self-duplication & inheritance. • 3. Expression of the genetic message. • DNA’s major function is to code for proteins. • Information is encoded in the order of the nitrogenous bases.
Prokaryotic Circular Very small 1 chromosome per cell Some enzymes and proteins are associated with the DNA. Not housed in a nucleus. Eukaryotic Linear Fairly long Several chromosomes per cell. Histone proteins---”spools”. Same in all eukaryotes Housed in a nucleus. Nucleosome—2 loops of DNA wrapped around 8 histone proteins. Unity theme. Chromosomes
DNA mRNA Proteins Traits Replication Unzip Template Floating nucleotides Template Sense strand Semiconservative Replication DNA Polymerase Proofreading functions 5’ to 3’ only Replication fork Discontinuous assembly Okazaki fragments Central Dogma of Genetics
RNA • 3 types—mRNA, tRNA, rRNA • Ribose • Uracil replaces Thymine • Single stranded helix
Transcription • RNA polymerase • Messenger RNA • mRNA • Unzipping of DNA helix. • Sense strand or template strand • Codons • Genetic code
Ribosomes rRNA Large and small subunits Codons Initiator or start codon Methionine (AUG) Stop codons tRNA Initiation Chain Elongation Peptide bonds Chain termination Polysome Translation