Ch. 16DNA

DNA: the Central Dogma, history, structure

Replication

History: timeline, people and their accomplishments

Mendel (heredity) Sutton Chromosomes Thomas Hunt Morgan (flies, linkage) Griffith (1928) transformation and mice Avery and colleagues (1944):

proposed DNA as the transforming agent Chargaff (late 40’s-early 50’s)

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

DNA Replication details

Griffith: Transformation

Hershey / Chase (the hereditary material is not a protein)

Radio-active P and S

Whose rule? A-T C-G

Purine? Pyrimidine?You have 6 billion pair

in every cell!

Chargaff’s Rule Purines (A, G, double rings) always pair

with Pyrimidines (T, C, single rings) A-T, C-G (& in RNA? ____) Old AP test question: if in a cell the

DNA bases are 17% A’s then what are the %’s of the other bases?

CUT your PY or Pure Silver (Ag)

DNA Replication:

SEMICONSERVATIVE MODEL

How did they (Meselson-Stahl) prove this? FIG 16.8

KNOW: Steps of ReplicationEnzymesLeading and Lagging strands Okazaki FragmentsAnti-parallel

Video

This process is fueled by…nucleoside nucleoside triphosphatestriphosphates

Semi-conservative

“Bubbles”

Replication forks,

simultaneous replication

**Eukaryotes - multiple

origins of replication

**Prokaryotes have one

DNA is made from DNA is made from 5’ to 3’5’ to 3’ and it is and it is read from 3’-5’.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?What do the terms 5’ and 3’ mean?

Leading & Lagging strands, made 5’-3’

Okazaki Okazaki fragmentsfragments (are (are of the lagging of the lagging

strand)strand)ENZYMES: helicase, DNA Polymerase, ligase

Enzymes :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 Leading Strand

(Nobelprize.org) Lagging Strand

(Nobelprize.org) Overall

(wiley) Overall 3D view

(wehi.edu.au or dnai.org)(Youtube has a music version)

Telomeres 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?

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.