Powerpoint presentation in DNA of living organisms
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Transcript of Powerpoint presentation in DNA of living organisms
DNAStructur
e
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 C – triple hydrogen bond
Nucleotide (3 chemical groups) Sugar – deoxyribose
contains 5 Carbon atoms
Phosphate group A base (A, T, G, C)
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
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
The most common organic bases are
Adenine
(A)
Thymine (T)
Cytosine (C)
Guanine (G)
The bases
The deoxyribose, the phosphateand one of the bases
adenine
deoxyribose
PO4
Combine to form a nucleotide
Nucleotides
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
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
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
2-stranded DNA
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
PO4
PO4
PO4
thymine
PO4
PO4
PO4
PO4
adenine
cytosine
PO4
guanine
Bonding 2
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
Pairing up
The paired strands are coiled into a spiral called
A DOUBLE HELIX
sugar-phosphatechain
bases
THE DOUBLE HELIX
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
Physical Structure (cont’d)
FORMS OF DNA
Supercoiling
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
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)
A DIY model ofpart of a DNA molecule
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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