Watson & Crick

In the mid 20th century, two scientists, James Watson and Francis Crick made the first model of DNA out of scrap metal. This model was in the shape of a double-helix. Rosalind Franklin is though to have first discovered the shape of DNA through x-ray images although she never received credit for it.

Edwin Chargoff

In 1950 Chargoff discovered two things about DNA. The first, is that the amount of thymine is equal to the amount of adenine (T=A), and that the amount of cytosine is equal to the amount of guanine (G=C). The second, is that the DNA to a specific species has different amount of adenine and guanine than other respective species.

How do the base pairs bind?

The strand of nucleotide binds in this sequence - Adenine binds to Thymine and Guanine binds to Cytosine. These strands are held together by hydrogen bonds.

What is a chromosome?

A chromosome contains DNA as well as proteins. The chromosome carries the majority of genetic information in a cell. Each chromosome has one molecule of DNA, and when a cell is about to divide the chromosomes are duplicated so that each cell has the correct amount of chromosomes. The amount of chromosomes in each cells varies by specific species. (humans have two sets of 23 per cell)

What is a karyotype?

A picture displaying someone's chromosomes. (diploid set of 23)

How does DNA replicate?

Right before a cell divides, its chromosomes are duplicated via DNA replication. During the replication enzymes break the hydrogen bonds that hold the strands together. After this process is completed, both chromosomes have two molecules of DNA which then attach at a part of the chromosome called the centromere which links the to chromosomes, or sister chromatids, together.

What damages DNA?

A multitude of bad things can happen to DNA. It can be mutated or damaged in a variety of ways. Some ways mutations can occur are when a different base is added to a growing strand of DNA, if one nucleotide gets lost, or if one nucleotide gets added. X-rays radiation as well as radiation from UV Light and gamma rays can lead to damaged DNA or broken DNA.

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