Chapter 8 By Will Dean

Watson and Crick

Watson and Crick were two experimenters who theorized the shape of DNA. Using models of metal, these two scientists came up with the idea that DNA was shaped in a double-helix.


Chargaff's rule stated that the DNA from any cell of all organisms should have the same ratio of pyramidine and purine bases. The amount of guanine should equal the amount of cytosine and the amount of adenine should equal the amount of thymine. If every DNA has they same amount, genetic differences form from the order of these base pairs.

The bond between Adenine and Thymine

Two bases in a strand of DNA bind themselves together by hydrogen bonds. These bonds do not involve the exchange electrons, rather they attract magnetically to opposite poles of molecules.


A chromosome is an extremely small structure that holds most, if not all of an organism's hereditary information. A chromosome holds DNA and other associated proteins. The amount differs from organism to organism, but us humans have 46. Chromosomes organize themselves into pairs. Humans have 22 pairs that are called autosomes and one pair that determines the sex.

Karyotype chart

Karyotype is the appearance or number of chromosomes in an organism's cells. The karyotype differs from organism to organism.

Replication of DNA diagram

The process of DNA replication is a necessary trait for our cells to have. Without it, our genetic information could not be passed on to future generations. To begin the process, a helicase protein splits the double helix of DNA into two halves, thus forming the replication fork. Next, a primase protein binds 10 RNA bases to the leading strand, thus forming the primer. After, the DNA polymerase binds DNA bases to the rest of the strand, making that strand the leading strand. In the lagging strand, a primase binds RNA bases to make the primer. Then, a DNA polymerase forms the Okazaki fragment, filling the gap between the primer and the other primer. Next, an exonuclease breaks off the RNA bases of the second primer and is replaced by DNA bases by the DNA polymerase. Finally, DNA ligase twist the strands and two new DNA's are created.

Damaged DNA

DNA can be damaged by reactive species of oxygen, nitrogen and carbonyl. Hydrolysis cleaves DNA as well. In large amounts, even alcohol and cigarettes can damage your DNA.

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Will Dean

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