DNA and RNA intro and experiments

 What is DNA?

DNA is a polymer of four types of nucleotides. Each nucleotide has a deoxyribose sugar, three phosphate groups, and a nitrogen-containing base. The nitrogen containing base is what the DNA is named after. The following are the names of the nitrogen containing bases: adenine (A), guanine (G), thymine (T), and cytosine (C). 


DNA structure:

A DNA molecule has two chains (strands) of nucleotides running in opposite directions and coiled into a double helix. Covalent bonds link the deoxyribose (sugar) of one nucleotide to a phosphate group of the next, forming the sugar–phosphate backbone of each chain. Hydrogen bonds between the internally positioned nitrogenous bases hold the two strands together.




Chargaff’s first rule:

First, the amounts of thymine and adenine are identical in any DNA molecule, as are the amounts of cytosine and guanine (A = T and G = C). We call this discovery Chargaff ’s first rule


Experiments with DNA: 

Griffith -

First experiment showed that R cells were harmless. When injected into mice, the bacteria multiplied, but the mice remained healthy.

The second experiment showed that an injection of S cells caused mice to develop fatal pneumonia. Their blood contained live S cells.

For a third experiment, Griffith killed S cells with heat before injecting them into mice. The mice remained healthy, indicating that the heat-killed S cells were harmless.

In his fourth experiment, Griffith injected a mixture of heat-killed S cells and live R cells. To his surprise, the mice became fatally ill, and their blood contained live S cells.Griffith discovered that hereditary information passes between two strains of bacteria (R and S)


Avery -

Used a process of elimination by treating bacterial extracts with enzymes that destroyed different cellular components like protein, RNA, and DNA, then testing the remaining extract for its ability to transform non-virulent bacteria. Only when DNA was destroyed did the transforming ability of the extract disappear, indicating DNA as the "transforming principle" responsible for genetic transfer

Hershey and Chase -

In the late 1940s, Alfred Hershey and Martha Chase proved that DNA, and not protein, satisfies the first expected property of a hereditary molecule: It transmits a full complement of hereditary information. Hershey and Chase worked with bacteriophage, a type of virus that infects bacteria. Like all viruses, these infectious particles carry hereditary material that specifies how to make new viruses. After a virus injects a cell with this material, the cell starts making new virus particles. Hershey and Chase carried out a series of experiments proving that the material a bacteriophage injects into bacteria is DNA, not protein.


What is RNA?

RNA is a molecule that is responsible for acting as a copy of DNA (more on this later). RNA is single stranded and made up of Ribose sugar (DNA is made up of deoxyribose sugar).



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