Aportion of an mrna attached to a ribosome reads: 5 gaccaga 3
if a trna with a histidine amino acid attached is in the p site of the ribosome, a trna with which amino acid attached will enter the a site?
tyrosine
a) phenylalanine
b) proline
c) serine
d) aspartic acid

The correct answer is a) a) phenylalanine

Explanation:

Every triplet codon in the mRNA codes for an amino acid. These amino acids are attached to the acceptor arm of a tRNA. Each tRNA carries a specific amino acid according to the sequence of anticodon it has which is complementary to the triplet codon present on mRNA.

A new tRNA enters through A site of a ribosome and P site is occupied by a previous tRNA. Therefore a new tRNA binds to the next three triplet codon of mRNA when it moves towards the P site.

CAU is the codon that codes for histidine(5 GACCAGA 3) amino acid and in the question P site have tRNA with histidine as attached amino acid so the next three codons are UUU(5 GACCAGA 3) which codes for phenylalanine so a tRNA that have attached phenylalanine will enter through A site of the ribosome.

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