The Molecular Basis of Inheritance Campbell Biology – Chapter 16

DNA Structure and Replication Cell Nucleus Deoxyribose Nucleic Acid Chromosomes DNA

DNA It’s Unique: Only molecule found in nature to direct its own replication. Directs the development of: Biochemical Anatomical Physiological Behavioral

Search for genetic material: Why most scientists thought it was protein? Great heterogeneity, specificity Little known about nucleic acids Chromosomes consist of: DNA Protein

Evidence of DNA transformation

change of phenotype due to assimilation of external stimuli pathogenic non-pathogenic Transformation: change of phenotype due to assimilation of external stimuli

Avery, McCarty, MacLeod Purified DNA from the heat-killed “S” cells and they transformed “R” cells. Scientists still believe protein is the hereditary material? Why? Know a lot about it. Biochemical control (enzymes) Lots of variation (20 amino acids)

More Evidence for DNA: Hershey and Chase

Additional Evidence for DNA In eukaryotes (like you): Mitosis – DNA is doubled Diploid cells have 2X the DNA as haploid Chargaff’s Rules (see #3) Species Specific: ratios of bases vary from species to species Adenine = Thymine Guanine = Cytosine

James Watson and Francis Crick: Discovered the structure of DNA in 1953. Discussed probable mode of replication.

Phosphate, Sugar and a Base Cytosine Without Guanine DNA Song We Love DNA Made of Nucleotides Phosphate, Sugar and a Base Bonded Down One Side Adenine and Thymine Make a Lovely Pair Cytosine Without Guanine Would Feel Very Bare

What’s a Nucleotide? Phosphate Base Sugar

DNA includes 4 nitrogenous bases: Adenine pairs with Thymine Pyrimidines Purines Guanine pairs with Cytosine

DNA is double stranded: Hydrogen bond connects the base pairs. Double Helix

DNA Model P G A T P S A S P S C P S T P

D = Deoxyribose Pentose Sugar: 5 sides

DNA Replication

Complementary Strands Separate

Parent Strands Serve as Template

Nucleotides connected

3 possible modes of replication: 15/15 14/14 3 possible modes of replication:

1st Replication found 14.5 density: 14 14.5 14.5 15

2nd replication found 14 and 14.5

DNA Replication:

Antiparallel Strands: Sugar-phophate backbones run in opposite directions.

DNA Polymerase can only work in a 5’ to 3’ direction. “Glues” the Okazaki fragments together. DNA Polymerase can only work in a 5’ to 3’ direction. Made continuously as the strand unwinds. Made in chunks and later connected.

Primase is the enzyme that joins the RNA nucleotides to make the primer. The primer is an RNA stretch that jump starts replication.

Proofreading and Repairing