Ch 16 DNA the Central Dogma history structure

Ch. 16 DNA: the Central Dogma, history, structure Replication

History: timeline, people and their accomplishments n n n Mendel (heredity) Sutton Chromosomes Thomas Hunt Morgan (flies, linkage) Griffith (1928) transformation and mice Avery and colleagues (1944): n n Chargaff (late 40’s-early 50’s) n n proposed DNA as the transforming agent base pairing (AT CG) Hershey-Chase (1952) DNA IS hereditary material Watson and Crick (1953) (Franklin) chemical structure of DNA Meselson-Stahl mid 1950’s n DNA Replication details

Griffith: Transformation

Hershey / Chase (the hereditary material is not a protein) Radioactive P and S

Whose rule? Purine? Pyrimidine? You have 6 billion pair in every cell! A-T C-G

Chargaff’s Rule Purines (A, G, double rings) always pair with Pyrimidines (T, C, single rings) n A-T, C-G (& in RNA? ____) n Old AP test question: if in a cell the DNA bases are 17% A’s then what are the %’s of the other bases? n n CUT your PY or Pure Silver (Ag)

DNA Replication: SEMICONSERVATIVE MODEL How did they (Meselson-Stahl) prove this? FIG 16. 8

KNOW: Steps of Replication Enzymes Leading and Lagging strands Okazaki Fragments Anti-parallel Video

“Bubbles” Replication forks, simultaneous replication **Eukaryotes - multiple origins of replication Semi-conservative This process is fueled by… nucleoside triphosphates **Prokaryotes have one

DNA is made from 5’ to 3’ and it is read from 3’-5’. The 3’ end is the end which elongates (grows) Why is this direction important to consider in Replication?

What do the terms 5’ and 3’ mean?

Leading & Lagging strands, made 5’-3’ Okazaki fragments (are of the lagging strand) ENZYMES: helicase, DNA Polymerase, ligase

Enzymes : • Helicase • Single strand binding proteins • Primase (RNA Primer) • DNA Polymerase • Ligase • Nuclease and DNA Polymerase (both are repair enzymes)

Let’s see this in Action n n Leading Strand (Nobelprize. org) Lagging Strand (Nobelprize. org) Overall (wiley) Overall 3 D view (wehi. edu. au or dnai. org) (Youtube has a music version)

Telomeres Unfilled gap left at the ends of the DNA strands due to the use of RNA primers Eventual shortening of DNA over time

Enzyme: Telomerase extends the (3’) long strand so the 5’ strand can finish. Telomerase is found in germ cells that give rise to gametes.

How’s it all fit? n DNA coiling – Let’s see it! DNA from a single skin cell, if straightened out, would be about six feet long but invisible. Half a gram of DNA, uncoiled, would stretch to the sun. Again, you couldn't see it.