DNA The Code of Life

Important Facts 1.DNA is the basic substance of heredity *Remember that heredity is the passing on of traits from an organism to its offspring 2.DNA stores and passes on genetic information from one generation to the next 3.Chromosomes are made of DNA

Important Facts 4.Genes are found on chromosomal DNA  DNA is a very large molecule with one molecule making up each chromosome  Each gene is only a small portion of the chromosome that it is on  Each chromosome carries many genes.  Therefore each DNA molecule carries many genes.

Who Discovered the Structure of DNA? It was in 1953, while working in Cavendish Laboratory in Cambridge, England, that the British-born Crick, then 36, and American-born Watson, 24, hit upon the famous double-helix structure -- like a twisted ladder -- of deoxyribonucleic acid, or DNA.

Who Discovered the Structure of DNA? Watson and Crick used X-ray crystallography data, produced by Rosalind Franklin and Maurice Wilkins at King's College in London, to decipher DNA's structure. For their work on DNA, Watson and Crick would later share the Noble prize with Wilkins. In what many see as an unfortunate injustice, Franklin was not also awarded the Noble prize, perhaps because she was already deceased by the time it was awarded.

DNA X-ray Crystallography Image Author: I.C. Baianu et al.

The Structure of DNA The DNA molecule forms a double-helix A double-helix looks something like a twisted ladder

What are the parts of a nucleic acid molecule (DNA or RNA)? DNA is composed of three types of molecules: A phosphate group A nitrogen base A sugar molecule These three parts combine to form nucleotides that are the building blocks of the DNA molecule (similar to the way amino acids make up proteins).

What are the parts of a nucleic acid molecule (DNA or RNA)? Parts of a DNA molecule: To make RNA instead, substitute Ribose sugar for the Deoxyribose sugar.

How do nucleotides form DNA? The sugar and phosphate groups alternate to form the sides of the “ladder” The “rungs” or “steps” are pairs of nitrogen bases joined by hydrogen bonds. Image modified from:

The Four Nitrogen Bases In DNA there are only four nitrogen bases: Adenine (A) Guanine (G) Cytosine (C) Thymine (T) When the opposing pairs join up Adenine always joins with Thymine and Cytosine always joins with Guanine. Credit: Madeleine Price Ball A_chemical_structure.svg A_chemical_structure.svg

What makes genes? The order of the nitrogen bases determines the genes on a chromosome. That is why DNA is said to carry the genetic code – the code is the order of the nitrogen bases. Each chromosome has million base pairs. Humans have about 2.9 billion base pairs.

DNA Replication In order for DNA to carry the genetic code there must be a way to accurately copy that code each time a cell reproduces. The copy must be an exact duplicate. This is accomplished through the process known as DNA replication.

DNA Replication First the DNA molecule “unzips” – the two strands separate between the base pairs. Next, two new strands are made by adding nucleotides one at a time, matching up the new nitrogen bases to the existing bases. The end result is two, double strands that are identical to the original one.

DNA Replication Step 1: The two sides of the DNA molecule unzip between the nitrogen bases Step 2: Free nucleotides match up to the nucleotides of each strand. Final Result: Two strands that exactly match the original strand and each other. Beginning Strand of DNA