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Nucleic Acids. Components of DNA. DNA is composed of four kinds of nucleotides , each of which consists of – a five carbon sugar ( deoxyribose ) – a phosphate group (PO4-) – one of four bases – adenine (A), guanine (G), thymine (T), or cytosine (C). Nucleotides. - PowerPoint PPT Presentation
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Nucleic Acids
DNA is composed of fourkinds of nucleotides, eachof which consists of– a five carbon sugar (deoxyribose)
– a phosphate group (PO4-)
– one of four bases – adenine(A), guanine (G), thymine(T), or cytosine (C)
Components of DNA
Thymine and Cytosine
NucleotidesAdenine and
Guanine
Edwin Chargaff, in 1949,noted two critical bits of data
The four kinds of nucleotide bases makingup a DNA molecule differ in relativeamounts from species to species
Rosalind FranklinUsed x-ray diffraction techniques
to produce images of DNA molecules.
She concluded:1. DNA exists as a long, thin
molecule of uniform diameter.2. The structure is highly
repetitive.3. DNA is helical.
Patterns of Base Pairing
Watson and Crick used
numerous sources of data to
build models of DNA.
The bases were hydrogen bonded (a weak bond) together in the
center of the helix.
– T (a pyrimidine) had twohydrogen bonds with A (apurine)
– C (a pyrimidine) had threehydrogen bonds with G (apurine)
Patterns of Base Pairing
The backbone wasmade of chains ofdeoxyribose sugarcovalently bonded (astrong bond) tophosphate groups.
The phosphate groupis bonded to the 3’carbon of onedeoxyribose, and the5’ carbon of another.
Patterns of Base Pairing
Each sugar ofthe backbone iscovalentlybonded to thenitrogenousbase off ofcarbon 1.
Patterns of Base Pairing
There are 10base pairsper turn ofthe helix.
Patterns of Base Pairing
The two sides are anti-parallel,meaning that the sugar andphosphates are running inopposite directions.• Each side ends in a phosphate(5’ end) and a sugar (3’ end)
Since the sides are anti-parallel,one side goes in the 3' to 5'direction, and the other goes inthe 5' to 3' direction.
Patterns of Base Pairing
The base pairing is constant for all species, but the sequence of base pairs in a nucleotide strand is different from one species to the next.
Where is DNA Located?Prokaryotes
bacteria and ArchaeaCircular DNA in
a region calledthe nucleoid
Plasmid
EukaryotesInside the nucleusLinearHighly coiled
Set of eight proteins called histones act as spools to wind the DNA into units called nucleosomes which form additional loops called a chromosome.
Where is DNA Located?
Inside mitochondriaand chloroplastsCircular“Naked” – not
associated withprotein