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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 Franklinin1953
concluded that DNAthe material which contains the genetic code
is made up of adouble helix
Hershey & Chasein 1952
showed that the genetic materialwas made up of nucleic acids
not protein
DNA Replication
leading strand5 to 3 directionlagging strand
Okazaki fragmentsDNA polymerases
DNA ligase (ligature)trombone model
see pages 323, 324, & 325
when DNA is copiedthe double strand opens up
the base pairs pull apartand enzymes and RNAs
start making a new double strandfor each of the separated strands
resulting in 2 identical DNAs
chromatin condensation
see fig. 16.22
DNA of 1 chromosomeif
stretched out would be100s of times longer than a cell
so how dies it get to fit
in a cell
see fig. 16.22
1 – the helix wraps around histone proteins (nucleosomes)
2 – nucleosomes pack or wrap into a fiber (string like)
3 – fiber formed into multiple loops4 – loops coil and fold into a chromosome
this is one explanation – is it the correct one ???????
Look at fig. 16.23b
the tangled mass of chromatinlooks to be without and order
butin reality
the chromatin of each chromosomeoccupies a specific part of the nucleus
the chromatin of each chromosomeoccupies a specific area
within the interphase nucleusand is called
heterochromatin
the dispersed chromatin is known as euchromatin