DNA Structure Discovering the structure of DNA DNA

DNA Structure

Discovering the structure of DNA • DNA = Deoxyribose nucleic acid • Made out of sugars (deoxyribose), phosphates and nitrogen bases

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

Discovering the structure of DNA • Structure was discovered in 1953 by James Watson and Francis Crick

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) 6

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

Discovering the structure of DNA Rosalind Franklin’s DNA image “Chargoff’s rule” A = T & C = G

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 14

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 16

How Chemical Bonds hold DNA together Covalent bondsbetween sugar & phosphates of 2 nucleotides Hydrogen bondsbetween complementary nitrogenous bases www. molecularstation. com/dna-structure/

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