DNA

Deoxyribonucleic acid

DNA is a nucleic acid• A nucleic acid is a polymer of nucleotides

• A nucleotide is made from a phosphate, sugar and base.

• www.chemsoc.org

Phosphate

• From phosphoric acid• http://bio.winona.edu/berg/ChemStructures/Phospha2.gif

Sugar

• Deoxyribose in DNA (Ribose in RNA)• http://www.mun.ca/biology/scarr/Deoxyribose_vs_Ribose.gif

Base• http://138.192.68.68/bio/Courses/biochem2/GeneIntro/GeneIntroResources/DNABases.gif

Purines• http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/notes/chpt14/purine.gif

Pyrimidines• http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/notes/chpt14/pyrimidine.gif

Nucleotide• Condensation between the phosphate and

sugar (at C5) and between the sugar (at C1) and base

• http://distancelearning.ksi.edu/demo/bio378/DNA_files/image002.gif

Dinucleotide• Two nucelotides join by condensation• http://pages.towson.edu/jdrawn/Chapter_1_Intro_to_Bioinfo_files/image005.jpg

• Condensation gives phospho diester bridge

Polynucleotide• Up to 5 x 106 nucleotides long• http://seqcore.brcf.med.umich.edu/doc/educ/dnapr/oligo.gif

• 5’ end

• 3’ end

DNA double helix

• The bases of the DNA nucleic acid form H bonds to bases of a second molecule of DNA

Table from Biological Science – Green, Stout, Taylor

• A is the same amount as T

• G is the same amount as C

• Amount of purines equals the amount of pyrimidines

• A always bonds to T

• G always bonds to C

• A bonds to T with two hydrogen bonds

• G bonds to C with three hydrogen bonds.• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/BasePairing.gif

• The two nucleic acids wind into a double helix, with H bonds between polar groups of sugars keeping the shape of the helix.

• (diagram from Bioligical Sciences, green, Stout & Taylor)

• The two strands are ANTIPARALLEL

• i.e. they are parallel, but run in opposite directions.

http://www.accessexcellence.org/RC/VL/GG/images/dna2.gif

Arrangement of DNA in chromosomes

http://www.biology.emory.edu/research/Lucchesi/multimedia/images/insert2.jpg

Histones in nucleosome• DNA is wrapped around a group of 8

histone proteins and held together by another histone molecule

• http://employees.csbsju.edu/hjakubowski/classes/ch331/dna/nucleosome.gif

• Nucleosomes:

• Help in supercoiling of DNA

• Help to regulate transcription