Question

A part of an mRNA molecule with the following sequence is being read by a ribosome: 5'-UGC-GCA-3' (mRNA). The charged transfer RNA molecules shown in the figure below (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form:
Which of the following dipeptides will be formed?

Proline-Threonine
Glycine-Cysteine
Alanine-Alanine
Cysteine-Alanin

Answer 1

mRNA codons determine which amino acid will be added to the growing polypeptidic chain. tRNA anticodons pair these codons and add the correct amino acid. The dipeptide formed will be Cysteine-Alanine.

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Let us review a few points,

• In protein synthesis, the ribosome reads mRNA in the 5´ to 3´ direction.

• According to the codons being readen, tRNA transfers the correct amino acids to build the polypeptide chain.

• A codon is a short sequence of three nucleotides that store the genetic information for the aminoacids´ assembly.

• Each codon represents one amino acid used to build the protein.

• Each tRNA has two important sites. One of them that couples with the codon of the mRNA molecule, named anticodon. The other site couples with an amino acid.

• The anticodon is a short sequence of bases that pairs with mRNA codons.

• tRNA adds amino acids following the codons sequence in the mRNA molecule.

• The protein grows from the amino terminus to the carboxy terminus.

• Adenine forms pairs with Uracyl ⇒ A↔U

• Guanine pairs with Cytosine ⇒ C↔G

In the exposed example,

→ mRNA     ⇒  codons   ⇒ 5'-UGC - GCA-3'

→ tRNA       ⇒ anticodons ⇒  ACG  CGU

→ proteins  ⇒ amino acids ⇒  Cys     Ala ⇒ Codon UGC codes for Cysteine

                                                                     ⇒Codon GCA codes for Alanine

So, for the given sequence of mRNA, tRNA anticodons are ACG and CGU. And the added amino acids are Cysteine and Alanine.

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Answer 2

Answer:

D

Explanation: