DNA was discovered in 1869 by Johannes Miescher. He determined that it was not a protein. He concluded that it is rich in nitrogen and phosphorus.

In the 1950's, James Watson and Francis Crick were two scientists who discovered the shape of DNA. They found that it was in the shape of a helix.

They were assisted in this find by Rosalind Franklin, who made the first clear x-ray diffraction image of DNA as it occurs in cells. She was not credited for the discovery because she died before Watson and Crick recieved the Nobel Prize for discovering DNA's shape.

In 1950, Erwin Chargaff created two rules based on his discoveries while studying DNA.

Chargaff's first rule- the amounts of thymine and adenine are identical, as are the amounts of cytosine and guanine.

Chargaff's second rule- DNA of different species differs in its proportions of adenine and guanine.

Structure of a DNA helix- Two sugar-phosphate chains running in opposite directions, and paired bases inside

- Bonds between the sugar of one nucleotide and the phosphate of the next form the backbone of each chain

- Hydrogen bonds between the internally positioned bases hold the two strands together.

- Only two kinds of base pairings form; A to T, G to C


A chromosome is a structure that consists of DNA and associated proteins. It carries part or all of a cell's genetic information.

Histone is a type of protein that structurally organizes eukaryotic chromosomes.

Nucleosome is the length of DNA wound twice around a spool of histone proteins.

A karyotype is an image of an individual's diploid set of chromosomes.

In preparation for division, a cell copies its chromosomes so that it contains two cells. The process in which a cell copies its DNA is called cell division

Before DNA replication, a chromosome consists of one molecule of DNA.

As replication begins, enzymes break the hydrogen bonds that hold the double helix together and the two DNA strands unwind and separate.

The establishment of base-replicating between two strands of DNA is called nucleic acid hybridization.

DNA polymerases attach to the hybridized primers and begin DNA synthesis.

The enzyme ligase seals any gaps, so the new DNA strands are continuous.

Both of the two strands of the parent molecule are copied at the same time As each new DNA strand lengthens, it winds up with its template strand into a double helix.

Semiconservative replication produces two copies of a DNA molecule: one strand of each copy is new, and the other is parental.

DNA can be either mutated or even damaged if either The wrong base is added to a growing DNA strand or nucleotide gets lost, or an extra one slips in.

Most replication errors occur because DNA polymerases work very fast. They can correct a mismatch by reversing the synthesis reaction to remove the mispaired nucleotide.

Mutations that alter DNA’s instructionsmay have a harmful or lethal outcome. These mutations could possibly lead to various cancers.

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