DNA replication -

Campbell and Reece, Chapter 16


It was not until the 1940's that it was proved that DNA was the material of heredity.
TRANSPARENCY (Fig. 16.1) (work of Griffith and Avery) S (smooth) bacteria kill mouse, R (rough) not, DNA from S can transform R to make them deadly.

To tell the next story, let us introduce reproduction in the bacteriophage (a virus that "eats" bacteria). Is a virus alive? Compare the terms "infectious" with "living." SLIDES (5) Is the virus the oldest form of life because it is so simple? (Made up of just Protein and DNA) No, it cannot be because it is a Parasite and therefore could not exits until its host existed.

TRANSPARENCY (Fig. 16.2 [a and b]) (Alfred Hershey & Martha Chase 1952 work) radioactive sulfur seen in protein coat of bacteriophage, radioactive phosphorus seen in bacteria where DNA is orchestrating the manufacture of new virus.

TRANSPARENCY (Fig 16.10 [Overview]) The fact that bases complement each other History:
means that each strand contains all the information necessary, put into action by each strand being capable of organizing the other strand; but instead of the two strands separating entirely and generating the daughter strand, numerous bubbles form where the parental strand is copied at the replication fork.

TRANSPARENCY (Fig. 16.13) 5'->3' direction replication fork
DNA helicase and leading strand DNA polymerase
lagging strand - primase makes RNA primer
DNA polymerase adds Okazaki fragment to RNA primer
primer removed and DNA replaced
DNA ligase fixes

TRANSPARENCY (Fig. 16.14) primase makes RNA primer

Mutations - variation and evolution
lots of repair mechanisms
TRANSPARENCY (Fig. 16.17) like excision of thymine dimers reacted from 260 nm light
ionizing radiation, chemicals, mistakes

TRANSPARENCY (Fig. 16.19) There are special problems at the telomeres (ends of the DNA molecules) because the above mechanisms cannot apply to both strands. Hence the need for telomerase to extend the 3' end. Eventually telomeres can become shorter.

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