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