Chapter 16 Molecular Basis of Inheritance Dr. Joseph Silver

we will study the following topics - DNA structure - DNA replication - chromatin condensation into a chromosome - heterochromatin - euchromatin

James Watson & Francis Crick & Rosalind Franklin in1953 concluded that DNA the material which contains the genetic code is made up of a double helix

Hershey & Chase in 1952 showed that the genetic material was made up of nucleic acids not protein

DNA Replication leading strand 5 to 3 direction lagging strand Okazaki fragments DNA polymerases DNA ligase (ligature) trombone model see pages 323, 324, & 325

when DNA is copied the double strand opens up the base pairs pull apart and enzymes and RNAs start making a new double strand for each of the separated strands resulting in 2 identical DNAs

chromatin condensation see fig

DNA of 1 chromosome if stretched out would be 100s of times longer than a cell so how dies it get to fit in a cell see fig

1 – the helix wraps around histone proteins (nucleosomes) 2 – nucleosomes pack or wrap into a fiber (string like) 3 – fiber formed into multiple loops 4 – loops coil and fold into a chromosome this is one explanation – is it the correct one ???????

Look at fig b the tangled mass of chromatin looks to be without and order but in reality the chromatin of each chromosome occupies a specific part of the nucleus

the chromatin of each chromosome occupies a specific area within the interphase nucleus and is called heterochromatin

the dispersed chromatin is known as euchromatin