4) Explain how complementary base pairing is used in replication, transcription and translation.  [10]

During replication one DNA strand is copied to make two identical DNA strands.

This occurs because the nucleotides are like ‘puzzle pieces’ and can only fit to one other nucleotide.

Adenine (A) can bond only to Thymine (T) and visaversa. 

Cytosine (C) can only bond to Guanine (G) and viceversa.

If each nucleotide could bond to two or more nucleotides, then there would be no precise way for replication to precisely copy the DNA code to produce 2 identical DNA strands.

The same occurs during transcription. The DNA code is copied into m-RNA code.

Cytosine (C) still bonds to Guanine (G) but the Thymine (T) is replaced by Uracil (U) in m-RNA.

Again the complementary base pairing rule means that DNA’s code is accurately converted to m-RNA code.

During translation the nucleotides of the m-RNA codon must be matched by the ribosome to the complementary anticodon nucleotides.

RNA base pairing rules apply here (A-U, C-G, etc.) Note that there is no T!

This ensures that the correct amino acid is placed in each position.  Thus the amino acid sequence originally specified by DNA occurs and the polypeptide is correctly made.