Chapter 15, Problem 1TYK

Eukaryotic mRNA:

usessnRNPs to cut out introns and seal together translatableexons.

uses a spliceosome mechanism made of DNA to recognizeconsensus sequences to cut and splice.

has a guanine cap on its 39 end and a poly(A) tail on its 59 end.

is composed of adenine, thymine, guanine, and cytosine.

codes the guanine cap and poly(A) tail from the DNAtemplate.

Summary Introduction

Introduction:

The messenger ribonucleic acid (mRNA) is that type of RNA that transcripts the DNA (deoxyribonucleic acid). RNA polymerase synthesizes a precursor of mRNA (pre-mRNA) in eukaryotes, which is then processed to form mRNA that is in a translatable form. The mRNA attaches to the ribosome where the amino acids bind to form polypeptide chains.

Answer to Problem 1TYK

Correct answer:

The eukaryotic mRNA uses snRNPs to cut out introns and seal together the translatable exons.

Explanation of Solution

Justification for the correct answer:

Option (a) states that the eukaryotic mRNA uses snRNPs to cut out introns and seal together translatable exons. The snRNPs (small nuclear ribonucleoprotein particles) bind to the pre-mRNA to form a complex spliceosome. The spliceosome breaks the pre-mRNA to remove nonprotein coding RNA sequences called introns and joins the coding RNA sequences named exons that can be translated. Hence, option (a) is correct.

Justification for the incorrect answers:

Option (b) states that eukaryotic mRNA uses a spliceosome mechanism made up of the DNA to recognize the consensus sequences to cut and splice. The spliceosome is a complex sequence formed by pre-mRNA and small nuclear ribonucleoprotein particles (snRNPs). The spliceosome breaks the pre-mRNA to remove the nonprotein coding sequences called introns. So, it is an incorrect option.

Option (c) states that the eukaryotic mRNA has a guanine cap on its 3′-end and the poly (A) tail on its 5′-end. The pre-mRNA process includes a capping enzyme that adds a cap at the 5′-end and at the 3′-end. The enzyme poly (A) polymerase adds a chain of adenine nucleotides at the 3′-end and 7-methylguanosine cap is added to the 5′-end of pre-mRNA. Thus, it is an incorrect option.

Option (d) states that the eukaryotic mRNA is composed of adenine, thymine, guanine, and cytosine. In the mRNA, there is uracil in the place of thymine. Both of these are pyrimidines that attach to adenine. So, it is an incorrect option.

Option (e) states that the eukaryotic mRNA codes the guanine cap and the poly (A) tail from the DNA template. This is incorrect because the guanine cap and the poly (A) tail in mRNA is not coded from the DNA template. A capping enzyme adds a cap at the 5′-end and at the 3′-end. The enzyme poly (A) polymerase adds a chain of adenine nucleotides, which makes the poly (A) tail of mRNA. So, it is an incorrect option.

Hence, options, (b), (c), (d), and (e) are incorrect.

Conclusion

Thus, it can be concluded that in the eukaryotes, small nuclear ribonucleoprotein particles (snRNPs) bind to the pre-mRNA to form a complex spliceosome. The spliceosome breaks the pre-mRNA to remove the nonprotein coding sequences called introns and joins the coding RNA sequences called exons, which can be translated.