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DNA, RNA and DNA Replication
IB Biology2011-2012
DNA History: DNA as Genetic Material
• Griffith: Pneumonia and Mice (1928)
DNA History: DNA as Genetic Material• Hershey & Chase
DNA History: DNA as Genetic Material
• Watson & Crick
• DNA is a nucleic acid, made of long chains of nucleotides
Structure of DNA
Nucleotide
Phosphate group
Nitrogenous base
Sugar
Polynucleotide Sugar-phosphate backbone
DNA nucleotide
Phosphategroup
Nitrogenous base(A, G, C, or T)
Thymine (T)
Sugar(deoxyribose)
• DNA has four kinds of bases, A, T, C, and G
Pyrimidines
Thymine (T) Cytosine (C)
Purines
Adenine (A) Guanine (G)
• RNA is also a nucleic acid
– RNA has a slightly different sugar
– RNA has U instead of T
Phosphategroup
Nitrogenous base(A, G, C, or U)
Uracil (U)
Sugar(ribose)
• Three representations of DNA
Ribbon model Partial chemical structure Computer model
Hydrogen bond
Representation of DNA: Chromatin to Chromosome
• Chargaff’s Rule• In DNA replication, the strands separate– Enzymes use each strand as a template to assemble
the new strands
DNA Replication: DNA replication depends on specific base pairing
Parental moleculeof DNA
Both parental strands serveas templates
Two identical daughtermolecules of DNA
Nucleotides
A
A
• DNA replication begins at specific sites
DNA Replication
Parental strandOrigin of replication
Bubble
Two daughter DNA molecules
Daughter strand
• Each strand of the double helix is oriented in the opposite direction
5 end 3 end
3 end 5 end
P
P
P
PP
P
P
P
• How DNA daughter strands are synthesized
5 end
P
P
Parental DNA
DNA polymerasemolecule
53
35
35
Daughter strandsynthesizedcontinuously
Daughter strandsynthesizedin pieces
DNA ligase
Overall direction of replication
53
• The daughter strands are identical to the parent molecule