DNA Structure DNA Structure DNA consists of two

DNA Structure

DNA Structure �DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. �In 1950’s, James Watson & Francis Crick determined model of DNA �A molecule of DNA is made up of millions of tiny subunits called Nucleotides. �Each nucleotide consists of: 1. Phosphate group 2. 5 -carbon (Pentose) sugar 3. Nitrogenous base

Nucleotides Phosphate Nitrogenous Base Sugar

DNA Nucleotide Phosphate Group O O=P-O O 5 CH 2 O N C 1 C 4 Sugar (deoxyribose) C 3 C 2 copyright cmassengale Nitrogenous base (A, G, C, or T) 4

Nucleotides �The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. �There are four types of nitrogenous bases.

Nucleotides A Adenine C Cytosine T Thymine G Guanine

Nucleotides �Each base will only bond with one other specific base. �Adenine (A) �Thymine (T) Form a base pair. �Cytosine (C) �Guanine (G) Form a base pair.

DNA Structure �Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

Chargaff’s Rule �Erwin Chargaff – Scientist: Discovered basepairing rules � The bases form the “rungs” on the DNA ladder by complementary pairing A == T C == G T == A G == C A == T T == A Sugarphosphate backbone

A T C G T A C G A T G C T A

Nitrogenous Bases �Double ring PURINES Adenine (A) Guanine (G) A or G �Single ring PYRIMIDINES Thymine (T) Cytosine (C) T or C copyright cmassengale 11

Four Nitrogen Bases of DNA �Pyrimidines: Nitrogeneous bases That have a SINGLE Ring of Carbon and Nitrogen Atoms. Ex. Cytosine and Thyamine �Purines: Nitrogeneous bases That have a Double Ring of Carbon and Nitrogen Atoms. Ex. Adenine and Guanine

Base-Pairings �Purines only pair with Pyrimidines �Three hydrogen bonds required to bond Guanine & Cytosine 3 H-bonds G copyright cmassengale C 13

DNA Structure �To crack the genetic code found in DNA we need to look at the sequence of bases. �The bases are arranged in triplets called codons. AGG-CTC-AAG-TCC-TAG TCC-GAG-TTC-AGG-ATC

DNA Structure �A gene is a section of DNA that codes for a protein. �Each unique gene has a unique sequence of bases. �This unique sequence of bases will code for the production of a unique protein. �It is these proteins and combination of proteins that give us a unique phenotype.

DNA Gene Protein Trait