Chapter 2C Molecular Basis of Inheritance Dr. Joseph Silver

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

James Watson & Francis Crick brought x rays to Rosalind Franklin in1953 and she 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

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

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

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 ???????

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

telomeres when DNA is replicated the very end of the lagging strand has no place for a primer and the end of the strand cannot be determined so RNA produces a complimentary strand and adds it to the end of the strand so the lagging strand can have an endpoint

the complimentary strand is a telomere so each time that strand is copied more telomeres are added which allows DNA polymerase to function

telomeres are abundant in germ, stem, & cancer cells in somatic cells DNA looses them and it is believed that when a cell stops making them it leads to aging

the process of DNA replication is very rapid laying down more than 1000 nucleotides per second the result is that mistakes are made which are usually corrected during replication

but some errors are passed on as mutations