A-LevelBiologyNucleic acids and protein synthesis9700/22 · Oct/Nov 2018 · Q57 Marks

DNA and RNA are nucleic acids.

(a)Explain why RNA can be described as a polymer and as a macromolecule.[2]
(b)The sugar component of DNA is a reducing sugar. Outline the test for reducing sugars and describe the observations for a positive result.[2]
(c)Nucleotides are structural components of nucleic acids. Each nucleotide consists of a pentose sugar, a phosphate group and a nitrogenous organic base. Complete Table 5.1 to compare DNA nucleotides with RNA nucleotides as structural components of nucleic acids. [Table 5.1][3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[1] polymer - context of a chain / strand (similar) repeating, smaller molecules / subunits or repeating / many, monomers / (RNA) nucleotides ; R branching A idea of nucleotides joined together to form a chain A made of nucleotides to form polynucleotide 'made of nucleotides' 'made of monomers' not enough
[1] macromolecule (in context of RNA) large (biological) molecules / 1000 or more atoms / high molecular mass ; A giant / huge, structure I long
[1] add Benedict's (solution / reagent) and, boil / heat to 95 °C ; A temperature 80 °C and above
[1] precipitate / (change from clear blue to) green / yellow / orange / red / brown ; R if a wrong colour included e.g. black / purple
[1] sugar component: DNA-deoxyribose, RNA-ribose;
[1] purine bases: DNA-adenine / A, guanine / G, RNA-adenine / A, guanine / G } ;
[1] pyrimidine bases: DNA-cytosine / C, thymine / T, RNA-cytosine / C, uracil / U } ; R thiamine for thymine

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