DNA encodes hereditary information in a chemical language.
All cells store their genetic information in the base sequence of DNA.
The genotype is determined by the sequence of bases.
Click to Access powerpoint presentation (thanks Speyside High)
1 The structure of DNA
Powerpoint Presentations on DNA structure
(a) Structure of DNA —nucleotides (deoxyribose sugar, phosphate and base), sugar–phosphate backbone, base pairing (adenine – thymine and guanine – cytosine), by hydrogen bonds and double stranded antiparallel structure, with deoxyribose and phosphate at 3′ and 5′ ends of each strand respectively, forming a double helix.
(b) Organisation of DNA – circular chromosomal DNA and plasmids in prokaryotes. Circular plasmids in yeast. Circular chromosome in mitochondria and chloroplasts of eukaryotes. DNA in the linear chromosomes of the nucleus of eukaryotes is tightly coiled and packaged with associated proteins.
2 Replication of DNA
(a) Replication of DNA by DNA polymerase and primer. Directionality of replication on both template strands. DNA polymerase adds complementary nucleotides to the deoxyribose (3′) end of a DNA strand. Fragments of DNA are joined together by ligase.
(b) Polymerase chain reaction (PCR) amplification of DNA using complementary primers for specific target sequences. DNA heated to separate strands then cooled for primer binding. Heat tolerant DNA polymerase then replicates the region of DNA. Repeated cycles of heating and cooling amplify this region of DNA. Practical applications of PCR.
