AS and A Level Biology

Describe the principle of the universal genetic code in which different triplets of DNA bases either code for specific amino acids or correspond to start and stop codons

Describe the differences between leading strand and lagging strand replication as a consequence of DNA polymerase adding nucleotides only in a 5′ to 3′ direction

Describe the linking of nucleotides by phosphodiester bonds

Differences in hydrogen bonding between C–G and A–T base pairs

Describe the importance of complementary base pairing between the 5′ to 3′ strand and the 3′ to 5′ strand (antiparallel strands)

State that the bases adenine and guanine are purines with a double ring structure, and that the bases cytosine, thymine and uracil are pyrimidines with a single ring structure (structural formulae for bases are not expected)

Interpret photomicrographs, diagrams and microscope slides of cells in different stages of the mitotic cell cycle and identify the main stages of mitosis

Outline the role of stem cells in cell replacement and tissue repair by mitosis

Explain how uncontrolled cell division can result in the formation of a tumour

Outline the role of telomeres in preventing the loss of genes from the ends of chromosomes during DNA replication