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