6.1.5: DNA structure (biology only)
Not started yet — this one needs some love.
DNA is a polymer made from four different nucleotides.
Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar.
DNA contains four bases: A, C, G and T.
A sequence of three bases is the code for a particular amino acid.
The order of bases controls the order in which amino acids are assembled to produce a particular protein.
The long strands of DNA consist of alternating sugar and phosphate sections.
The DNA polymer is made up of repeating nucleotide units.
Higher tier: in complementary strands, C is always linked to G and T to A.
Higher tier protein synthesis: proteins are synthesised on ribosomes, according to a template; carrier molecules bring specific amino acids in the correct order.
Higher tier protein shape: when the protein chain is complete it folds up to form a unique shape.
Higher tier mutations: most do not alter the protein, or only alter it slightly so that its appearance or function is not changed.
Higher tier mutations: a few code for an altered protein with a different shape.
Higher tier non-coding DNA: sections that do not code for proteins can switch genes on and off, so variations may affect how genes are expressed.
Common exam mistakes
A base triplet codes for an amino acid, not directly for a whole protein.
Higher tier: base pairing is A with T and C with G; do not pair A with C or T with G.
A mutation may have no effect, a small effect, or a large effect; not all mutations are harmful.
Do not add detailed mRNA or tRNA descriptions unless the question specifically gives that context.