Question

The first codon of uracil nucleotides, UUU was deciphered by
a. Mathaei
b. Khorana
c. Nirenberg
d. Both A and C

Answer 1

A nucleotide is composed of a nitrogenous base such as purine or pyrimidine, a pentose sugar, and phosphate groups. Nucleotides join and form a polymer which is called nucleic acid. Phosphodiester linkages join the nucleotides. All purine ring nitrogens such as N-1, N-3, N-7, and N-9 can form hydrogen bonds.

Complete answer:
Marshall Nirenberg and Heinrich Mathaei incubated synthetic polyuridylate with poly (U), GTP, ATP, and E.Coli extract. This also contains 20 amino acids in 20 different tubes containing a different radioactively labeled amino acid.
The poly (U) mRNA contains many UUU triplets, and therefore, the resultant polypeptides should contain only that amino acid that codes by the UUU triplet.

From these 20 tubes. One tube synthesized a radioactive polypeptide that contains radioactive polyuridylate.
From this experiment, it was concluded that triplet UUU encodes for polyuridylic.
After this experiment, Khorana used the same approach to determine that polycytidylate encodes a polypeptide that contains only proline, and polyadenylate encodes polylysine.

Hence, the correct answer is option (D).

Note: A codon is a three nucleotides sequence of mRNA that specifies the addition of specific amino acids. The codon is present on the coding strand of mRNA. The anticodon is found on the tRNA and is the part that base pairs with the codon to bring the appropriate amino acid to the ribosome.
A codon is a set of three base pairs sequences that are present on an mRNA strand. It corresponds to the specific amino acid or acts as a stop signal during protein synthesis. The nucleotides are abbreviated as A, U, G, and C. The anticodon is the complementary base pair.