DNA Replication DNA is copied – this is called replication Without DNA replication, a new cell would only have half of it’s information. All organisms undergo DNA replication

The original DNA now has a complimentary strand.

The result is two DNA molecules which is identical to the original.

DNA Replication Meselson and Stahl (1957) Process called semi-conservative replication

Experiment

DNA of heavy, light, and intermediate densities can be separated by centrifugation.

Experimental Results

Experimental Results

Semiconservative: 1 new strand (daughter)+ 1 old (parent)

RNA primase

Direction of replication

Direction of replication

Direction of replication

Direction of replication

Direction of replication

Replication Fork

Replication Fork

שים מעבר לתוכנית

לשם פעולתו של אנזים דנ"א פולימרז נחוצה נוכחותם של ארבעה גורמים:        i. תבנית דנ"א.       ii. רצף חד-גדילי הרנ"א משלים לאיזור התחלה של ההכפלה לתבנית דנ"א . רצף זה קרוי פרימר.      iii.  יוני Mg+2 (קופקטור של אנזים דנ"א פולימרז)      iv. ארבעה סוגי חומרי מוצא:dTTP, dCTP , dGTP , dATP .

DNA template with synthesis of a new strand in the 5' to 3' direction. The replication fork DNA template with synthesis of a new strand in the 5' to 3' direction.

The lagging strand fragments are called Okazaki fragments after their discoverer, Reiji Okazaki.

The RNA primers are removed

the fragments Okazaki are joined by DNA ligase.

   DNA template with synthesis of a new strand in the 5' to 3' direction.

RNA primers are used to initiate a new strand

The two antiparallel strands are replicated simultaneously in both directions.

The lagging strand fragments are called Okazaki fragments after their discoverer, Reiji Okazaki.

DNA structure predicts that base sequence determines replication of DNA

All DNA polymerases synthesize from 5' 3'

Enzymes/proteins in DNA replication in E. coli Helicase Unwinds DNA Primase Adds RNA primer single stranded binding protein Stabilizes DNA polymerase III Synthesizes DNA DNA polymerase I Erases primer,fills gaps DNA polymerase II uncertain DNA ligase Joins ends of DNA fragments

The two antiparallel strands are replicated simultaneously in both directions.

Replication Fork

Replication Fork -end