Date post: | 22-Dec-2014 |
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DNA
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
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 phosphodiester 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
• 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
• 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
• Known as Chargaff’s Rule
Table from Biological Science – Green, Stout, Taylor
• 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
DNA from a single skin cell, if straightened out, would be about six feet long but invisible. Half a gram of DNA,
uncoiled, would stretch to the sun. Again, you couldn't see it.