DNA Structure and Function. The Structure of DNA.
By the early 1950s, most scientist were convinced that genes were made of DNA. Two young researchers at Cambridge University, James Watson and Francis Crick, pieced together a model of the structure of DNA. They determined that it was a double helix – two strands twisted around each other like a winding staircase. Each strand is made of linked nucleotides. Nucleotides are the subunits that make up DNA. Each nucleotide is made of three parts: a phosphate group, a 5-carbon sugar molecule (deoxyribose), and a nitrogen-containing base which makes up DNA (deoxyribonucleic acid).
While the sugar and phosphate group are the same for each nucleotide, the nitrogen base may be any of the four different nitrogen bases in DNA: (A) adenine; (T) thymine; (C) cytosine; (G) guanine.
Adenine and guanine are classified as purines (nitrogen bases made of 2 rings of carbon and nitrogen atoms).
Thymine and cytosine are classified as pyrimidines (nitrogen bases made of a single ring of carbon and nitrogen atoms).
The double helix is held together by weak hydrogen bonds between the pairs.
Watson and Crick determined that a purine on one strand always paired with a pyrimidine on the opposite strand. For example, adenine (A) pairs with thymine (T) = (A-T); and guanine (G) pairs with cytosine (C) = (G-C).
Adenine forms 2 hydrogen bonds with thymine, and cytosine forms 3 hydrogen bonds with guanine. The hydrogen bonds between the nitrogen bases keep the two strands of DNA together.
Complimentary base pairs is the sequence of bases on one strand determines the sequence of bases on the other strand. For example, if the sequence of the nitrogen bases on one strand of a DNA molecule is TCGAACT, the sequence of nitrogen bases on the other strand must be AGTCTTGA.
DNA store the information that tells which proteins to make and when to make them.
DNA also contain the genetic material that passes traits from parent to offspring.
The genetic material that passes traits from parent to offspring is called genes.
The passing of traits from parents to offspring is called heredity.