Chapter 12

Chapter 12 - 12.1 The Hunt for Fame Fortune and DNA...

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Unformatted text preview: 12.1 The Hunt for Fame, Fortune and DNA DNA (deoxyribonucleic acid) acidic compound containing a bit of phosphorus; functions as cell's treasurehouse of inheritance. Its molecular structure encodes info required to reproduce parental traits in offspring Bacteriophages viruses used for experiments to infect certain bacteria; infectious particles contain info on how to build new particles and at some point after they infect a host cell, viral enzymes take over its metabolic machinery - Consist only of DNA and a protein coat; micrographs revealed that the coat remains on the outer surface of infected cells so DNA is genetic material of virus 12.2 The Discovery of DNA's Structure DNA contains only four kinds of nucleotides building blocks of nucleic acids consisting of a 5-C sugar, a phosphate group and one of the following N-containing bases; component parts organized in the same way - Adenine (A) has two carbon rings (purine) - Guanine (G) has two carbon rings (purine) - Thymine (T) has one carbon ring (pyrimidine) - Cytosine (C) has one carbon ring (pyrimidine) Watson and Crick perceived that DNA must consist of (2) strands of nucleotides, held together at their bases by hydrogen bonds which form when the two strands run in opposing directions and twist to form a double helix - Two kinds of base pairings form along the molecules length: A T and G C 12.4 DNA Replication and Repair Before Watson and Crick, no one could explain DNA replication how the molecule of inheritance is duplicated before a cell divides Enzymes easily break H-bonds b/w nucleotide strands of a DNA molecule - When enzymes and other proteins act on the molecule, one strand unwinds from the other and exposes stretches of its nucleotide bases - Cells contain stockpiles of free nucleotides that can pair with the exposed bases while parent strand stays intact - Half is "old" and half is "new" - Some enzymes unwind the strands in both directions and prevent them from rewinding DNA polymerases, a class of enzymes, attach short stretches of free nucleotides to unwound parts of parent template - Free nucleotides drive strand assembly, each with three P-groups. DNA polymerase splits off two, releasing energy that drives attachments - Can correct mismatched base pairs or replace mutated ones DNA ligases fill tiny gaps b/w new short stretches and form one continuous strand - Can also fix breaks in DNA Then, enzymes wind template and complimentary strands, forming DNA double helix 12.5 Reprogramming DNA to Clone Mammals Artificial twinning gives clones identical to one another but not to sexually reproducing parents Differentiated cells are faster b/c desired genotype is known - All cells descended from fertilized egg have same DNA but different lineages start making unique selections from it during development The selections commit them to becoming liver cells, blood cells, or other specialists in structure A differentiated cell must be tricked into rewinding the clock by nuclear transfer and then chemical/electrical shocks may induce the cell to divide ...
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