DP Biology 11DP Biology 11Unit 3.3DNA Structure

DNA StructureDNA Structure

DNA StructureDNA Structure

Nucleotide structure Sugar◦ Deoxyribose

Phosphate group◦ PO4

-3 group

Nitrogenous base◦ 4 different kinds of ring-based structures

DNA StructureDNA Structure

Nucleotide structure Nitrogenous base◦ C Cytosine◦ G Guanine◦ A Adenine◦ T Thymine

DNA StructureDNA Structure

DNA StructureDNA Structure

General structure Backbone:◦ Phosphate group of one nucleotide attaches to the

third (3’) carbon of the deoxyribose in the next◦ Deoxyribose - Phosphate - Deoxyribose –

Phosphate - etc...

Nitrogenous base attached to deoxyribose

DNA StructureDNA Structure

General structure

DNA StructureDNA Structure

DNA StructureDNA Structure

Formation of the DNA double helix Complementary base paring:◦ A = T Adenine forms two hydrogen bonds with its

complementary base, thymine

◦ G = C: Guanine forms three hydrogen bonds with its

complementary base, cytosine

DNA StructureDNA Structure

DNA StructureDNA Structure

Formation of the DNA double helix Hydrogen bonds:◦ Hydrogen bonds between A = T and G = C hold

the two strands of DNA together◦ Each strand forms a helix, the two strands

together form a double helix

DNA StructureDNA Structure

DNA StructureDNA Structure

DNA StructureDNA Structure

DNA StructureDNA StructureThis is image shows: Two polynucleotide chains Two anti-parallel chains◦ The two chains are in

opposite directions

A uniform distance (2nm) between the backbones

Complementary base pairs:◦ Adenine hydrogen binds to

Thymine◦ Cytosine hydrogen bonds to

Guanine

DNA StructureDNA StructureThis is image shows: DNA is double-stranded, ◦ The strands are antiparallel,

The strands are wound round each other to form a double helix (not a spiral)

The two strands are joined together by hydrogen bonds between the bases◦ Follow commplementarity◦ Sequence on one strand

complementary to the other

TOK QUESTION:TOK QUESTION:

PLAGIARISM in science!

To what extent was Watson and Crick’s “discovery” of the three dimensional

structure of DNA dependent on the use of data generated by Rosalind Franklin,

which was shared without her knowledge or consent?

Do they deserve full credit?

MAJOR SOURCESMAJOR SOURCESThank you to my favorite sources of information when making these lectures!

John Burrell (Bangkok, TH)www.click4biology.info

Dave Ferguson (Kobe, JA)

http://canada.canacad.ac.jp/High/49

Stephen Taylor (Bandung, IN)

www.i-biology.net

Andrew Allott – Biology for the IB DiplomaC. J.Clegg – Biology for the IB DiplomaWeem, Talbot, Mayrhofer – Biology for the International BaccalaureateHoward Hugh’s Medical Institute – www.hhmi.org/biointeractiveMr. Hoye’s TOK Website – http://mrhoyestokwebsite.com And all the contributors at www.YouTube.com