1. In 1961 biologists made synthetic mRNA. When they produced mRNA containing only uracil nucleotides, it coded for one type of amino acid, phenylalanine. When mRNA was produced with alternating uracil and guanine nucleotides, two types of amino acid were coded for, valine and cysteine. This is summarised in the table.

Nucleotide sequence in mRNA

Amino acids coded for




valine and cysteine

(a) For the amino acid phenylalanine what is

the corresponding DNA base sequence,



the tRNA anticodon?


(b)  Explain how the information in the table supports the idea of a triplet code.

NEAB 1998


The diagram shows the structure of a tRNA molecule.

(a)  Give two ways in which the structure of a tRNA molecule differs from that of a DNA molecule.


 Explain how the specific shape of the tRNA molecule shown in the diagram is determined by the pattern of bonding

(c) (i)

Give the base sequence of the anticodon of this tRNA molecule.


(ii) Which mRNA codon would correspond to this anticodon?

NEAB 1997