Published on March 7, 2014
Cellular composition DNA is contained in nucleus of cell Phospho-lipids and proteins combined to form cell membrane Lipids are fats
Base pairs A=T – double hydrogen bond G Nucleotide (3 chemical groups) C – triple hydrogen bond Sugar – deoxyribose contains Phosphate A 5 Carbon atoms group base (A, T, G, C)
DNA molecule DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of a sugar called deoxyribose a phosphate group -PO4 and an organic base
Ribose & deoxyribose Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule Deoxyribose is almost the same but lacks one oxygen atom Both molecules may be represented by the symbol
The bases The most common organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G)
Nucleotides The deoxyribose,the phosphatend one of the bases a Combine to form a nucleotide PO4 adenine deoxyribose
7 Joined nucleotides PO4 PO4 PO4 PO4 sugar-phosphate + bases backbone A molecule of DNA is formed by millions of nucleotides joined together in a long chain
In fact, the DNA usually consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases
2-stranded DNA PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4
Bonding 1 The bases always pair up in the same way Adenine forms a bond with Thymine Adenine Thymine and Cytosine bonds with Guanine Cytosine Guanine
Bonding 2 PO4 PO4 adenine thymine PO4 PO4 cytosine guanine PO4 PO4 PO4 PO4
Pairing up PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4
The paired strands are coiled into a spiral called A DOUBLE HELIX
THE DOUBLE HELIX bases sugar-phosphate chain
Physical Structure (cont’d) Chains are anti-parallel (i.e in opposite directions) Diameter and periodicity are consistent 10 bases/ turn 2.0 nm 3.4 nm/ turn Width consistent because of pyrimidine/purine pairing
Physical Structure (cont’d)
FORMS OF DNA
DNA is Dynamic Like proteins, DNA has 3º structure Why so many deviations from normal conformation? Enhances responsiveness Effects on transcription (gene expression) May also serve in packaging NOTE: most cellular DNA exists as protein containing supercoils
Denaturation of DNA Denaturation by heating. How observed? A260 For dsDNA, A260=1.0 for 50 µg/ml For ssDNA and RNA A260=1.0 for 38 µg/ml For ss oligos A260=1.0 for 33 µg/ml The T at which ½ the DNA sample is denatured is called the melting temperature (Tm) Hyperchromic shift
A DIY model of part of a DNA molecule
Accreditation to the following http://www.present.udel.edu/biotech/rD NA.html http://www.sumanasinc.com/webcontent/anisam ples/molecularbiology/plasmidcloning_fla.html http://www.worldofteaching.com
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