Chapter 8 Dan "el Padrino" Annunziato

James Watson and Francis Crick

James Watson and Francis Crick, from America and Britain respectively, communicated with one another about their ideas on DNA. They both believed that the structure of DNA was helical, just like the secondary structure of proteins. Rosalind Franklin helped them determine the chemistry of the DNA. His data helped Watson and Crick built the first DNA model.

Watson and Crick with their DNA model.
DNA base sequence, Chargaff Rule


A researcher who was trying to discover the function of DNA, Erwin Chargaff, came up with two rules. The first was that A=T and G=C, which means that the amount of thymine and adenine are equal and that the amounts of cytosine and guanine are equal His second rule states that although the amounts are equal, the proportions vary from species.

Binding of the base pairs

DNA bonds together in what's called the DNA sequence. Adenine and Guanine bond together with double hydrogen bonds, and thymine and Cytosine bond together with triple hydrogen bonds. The base pairs have sides that fit into one another, much like an enzyme and its substrate.


Chromosomes are structures that are formed by DNA and associated proteins. They also carry part or all of the cells genetic information.


Karyotypes are a unique set of chromosomes from an individual arranged by shape, length, size, and centromere location. These are usually displayed in an image, as above.

Replication of DNA

Enzymes break hydrogen binds holding the base pairs together, causing the DNA to unwind and separate. Another enzyme makes primers. These are single strands of nucleotides. The primers attach to polymerase, which constructs new DNA strands. Primers then pair with a complementary strand of DNA. This is called nucleic acid hybridization. Polymerases attach to the primers after hybridization to begin DNA synthesis. Ligase seals all gaps to continue DNA strands, and as this happens, it winds into a double helix. Two copies are the products: The new strand and the parent DNA

DNA Damage

When powerful rays of electromagnetic radiation, such as gamma rays, they knock electrons out of atoms, releasing radiation that can damage DNA. The radiation covalently bonds opposite strands, ending its ability to copy and produce more DNA. UV radiation opens the bonds in the bases, causing them to covalently bond with an adjacent base.


Created with images by thekirbster - "DNA" • mandam - "chromosome" • Hey Paul Studios - "Female Karyotype, 2014"

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