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AS Biology
Unit 2 Module 1: Molecules, biodiversity, food and health
OCR
Nucleic Acids
Understanding the structure of nucleic acids allows an understanding of their role in the
storage of genetic information and the functioning of the cell.
Key Words
Nucleotide. Nucleic acid. Polymer. DNA. RNA. Nucleus. Eukaryote
cell. Nucleus. Condensation. Protein. Deoxyribose. Thymine.
Organic base. Monomer. Covalent bond. Ribose. Adenine.
Guanine. Cytosine. Uracil. Ribose. Purine. Pyrimidine.
Polynucleotide. Hydrogen bond. Double helix. Complementary.
Base-pairing rules. Interphase. Chromatid. Semi-conservative
replication. Transcription. Messenger RNA. Ribosomal RNA.
Transfer RNA. Ribosome. Amino acid. Polypeptide. Peptide bond.
Primary structure. Secondary structure. Tertiary structure. Gene.
Chromosome. Allele.
You should be able to:
 State that deoxyribonucleic acid (DNA) is a polynucleotide, usually double-stranded,
made up of nucleotides containing the bases adenine (A), thymine (T), cytosine (C)
and guanine (G).
 State that ribonucleic acid (RNA) is a polynucleotide, usually single-stranded, made up
of nucleotides containing the bases adenine (A), uracil (U), cytosine (C) and guanine
(G).
 Describe, with the aid of diagrams, how hydrogen bonding between complementary
base pairs (A to T, G to C) on two antiparallel DNA polynucleotides leads to the
formation of a DNA molecule and how the twisting of DNA produces its ‘double-helix’
shape.
 Outline, with the aid of diagrams, how DNA replicates semi-conservatively, with
reference to the role of DNA polymerase.
 State that a gene is a sequence of DNA nucleotides that codes for a polypeptide.
 Outline the roles of DNA and RNA in living organisms (the concept of protein synthesis
must be considered in outline only).
Recommended reading
Core Text Book
Pgs 116-121
Toole & Toole, 4th Ed.
Pgs 109-118
NAS Molecules and Cells
Pgs 19-30