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