 This very large molecule called Deoxyribonucleic acid contains information.  DNA information codes for proteins that make up muscle, enzymes, & the structures of organisms.  A gene is a section of DNA coding for a protein.

 DNA has a uniform diameter (Franklin)  DNA is a double helix (Watson and Crick)  Adenine pairs with Thymine & Guanine pairs with Cytosine (Chargaff)  The two strands are built in opposite directions.

 Backbone or rails of the ladder: alternating deoxyribose and phosphate.  Deoxyribose: a sugar  Phosphate: a negative ion containing phosphorus  Alternating pattern

 Nitrogenous bases contain nitrogen  Pairs: › A-T › G-C  Pyrimidines: 1 ring › Thymine › Cytosine  Purines: 2 rings › Adenine › Guanine

 Hydrogen bonds connect A-T or G-C pairs.  H bonds are weak forces between partial positive and negative charges on atoms— works like magnets.

 Patterns of Inheritance  Gregor Mendel studied peas the and passage of traits from one generation to another. › What could carry the information from one individual to another?

 Experiment: mice and 2 types of pneumonia (virulent and non-virulent).  Proved chemical transfer of information.

 Chargaff studied the DNA of different species from different kingdoms and different phyla.  The amount of Adenine was close to equal to the amount of Thymine.  The amount of Guanine was close to the amount of Cytosine.  Chargaff’s Rule 

 Studied the structure of DNA using a technique called X- ray diffraction.  The repeating ‘x’ patterns imply a twisting coiled shape: helix.  The molecule has uniform diameter and uniform repeat to the twist.

 They worked to develop three dimensional model of DNA that would explain properties of the molecule.  Franklin’s work gave them a vital clue.  The molecule was a double helix with the bases making the rungs of a ladder.  One page paper was published April 1953

 To pass information to another organism, the data which is stored in the DNA must be copied.  Process is called DNA Replication  A replica is an exact copy  How does DNA replicate?  How does its structure work to make copies?

 Both strands carry the same information.  1) Unwind the helix.  2) Unzip the strands to make two templates to use in making copies.  3) Build a complementary strand one nucleotide at a time for two identical molecules. Replication Fork

 Follow Chargaff’s Rule: A=T and G=C  Find the bases that complement this strand: A T T T GCG TAACCGA TAAA CGCAT T GGCT

 Which model would work?

 Enzyme that unwinds the double helix.  Name comes from the helix shape of DNA that the enzyme straightens out. Helicase

 This protein enzyme that connects the nucleotides together to make the polymer.  It proofreads the sequences.  Most accurate enzyme Polymerase DNA Polymerase

 DNA is an enormously long molecule.  How do you pack and move DNA?  how-dna-is-packaged-basic.html how-dna-is-packaged-basic.html

 Wind DNA around histone core like a spool of thread.  Nucleosome  Wind coiled DNA into second supercoil.  Condensed chromosome

