Lesson #13DNA

The DNA moleculeDouble helix model

Rosalind Franklin - 1952

Image obtrained at: bio-chronicle.blogspot.comImage obtained at: www.poramoralaciencia.com

Photograph 51

James Watson and Francis Crick

1953

www.40innovadoresbbva.com

J. Watson F. Crick

Double helix model

In 1952 Rosalind Franklin proposed the DNA molecule is a

double helix and she made a photograph that helped

prove it.

In 1953 James Watson and Francis Crick described the

structure of the DNA molecule on NATURE magazine.

DNA is a molecule which packs and condenses with the

help of proteins (histones) to form a structure called

chromosome.

The DNA molecule contains the code or genes which make

an organisms structure and function.

Components of the DNA molecule

Formed by thousands of smaller units callednucleotides

Each nucleotide is made up of deoxyribose, a nitrogenous base and phosphate

There are 4 different nucleotides which differaccording to their nitrogenous base.

Adenine (A), cytosine (C), thymine (T) and guanine (G)

When nucleotides join together, they form a chainwhere deoxyribose alternates with phosphate groups.

Nucleotides: Nitrogenous bases

Deoxyribonucleic Acid (DNA)

DNA molecule made up of two, complimentary, antiparallel chains (strands) of nucleotides.

Antiparallel: The strands run in oppositedirections (5’ 3’ and 3’ 5’)so that thenitrogenous bases look towards the interior of the molecule.

Complimentary: The nitrogenous bases onopposite chains are complimentary and jointhrough hydrogen bonds.

Adenine (A) --- Thymine (T)

Cytosine (C) --- Guanine (G)

Both chains twist around each other in theshape of a double helix.