AP Biology : Understanding Post-Transcription Modification

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #979 : Ap Biology

Which of the following statements about post-transcriptional processing is true?

Possible Answers:

A methylguanine cap is added to the 3' end of the mature mRNA

Post-transcriptional hnRNA processing prevents RNA from degrading as it leaves the nucleus

A poly-A tail is added to the 5' end of the mature mRNA

Exons are spliced out of hnRNA and are not part of the mature mRNA

Correct answer:

Post-transcriptional hnRNA processing prevents RNA from degrading as it leaves the nucleus

Explanation:

The hnRNA (heterogeneous nuclear RNA) produced from transcription must be processed by several enzymes to create an mRNA (messenger RNA) product that can pass from the nucleus to the cytoplasm without degrading. This involves cutting out introns, which remain in the nucleus, and splicing exons together. Furthermore, a methylguanine cap is added to the 5' end and a poly-A tail is added to the 3' end. 

Example Question #2 : Understanding Post Transcription Modification

Which of the following is not an example of a post-transcriptional modification of mRNA molecules?

Possible Answers:

Addition of a 5-methyl guanosine cap

Splicing of introns

Addition of a poly-A tail

Splicing of anticodons 

Correct answer:

Splicing of anticodons 

Explanation:

Addition of a 5-methyl guanosine cap, the splicing out and removal of introns, and the addition of a poly-A tail are all processes that are essential to making stable, mature mRNA.

Codons are contained on the exons of mature mRNA and are matched to appropriate anticodons during translation. Anticodons are found on tRNA molecules, and are not involved in mRNA transcription.

Example Question #3 : Understanding Post Transcription Modification

Which biotechnology method will allow you to distinguish between identical twins?

Possible Answers:

DNA fingerprinting

Southern blot

Restriction fragment length polymorphism (RFLP) Analysis

Standard fingerprinting

Correct answer:

Standard fingerprinting

Explanation:

Fingerprints are different in all individuals, even identical twins. Due to RNA processing, or post-transcription modification, the grooves of a finger are different even in individuals with identical DNA.

The other techniques are used for DNA analysis between individuals with different DNA. Identical twins will be indistinguishable under these techniques, because their DNA is the same.

Example Question #4 : Understanding Post Transcription Modification

Which of the following statements is false concerning post-transcriptional modification?

Possible Answers:

A poly A tail is attached to the 3' end of the transcript

Methylation is not part of post-transcriptional modification

Both the 5' cap and poly A tail protect the transcript from degradation

A 5' cap is added in order to provide an attachment site for ribosomes during translation

Spliceosomes remove exons from the transcript and splice together the introns

Correct answer:

Spliceosomes remove exons from the transcript and splice together the introns

Explanation:

During post-transcriptional modification, spliceosomes can remove introns from the transcript and splice together exons. Introns are the parts that are removed from the transcript, meaning they are not translated. Exons are the portions of mRNA that code for the correct amino acids sequence for the desired gene.

Other modifications involve the poly-A tail, which is added to the 3' end, and the 5' cap. Both structures protect the transcript from damage during transport and provide binding sites for various proteins, as well as the ribosome itself. Methylation is a part of epigenetic DNA modification, and is not involved with transcription processes.

Example Question #5 : Understanding Post Transcription Modification

snRNPs assist in what post-transcriptional modification?

Possible Answers:

The removal of introns

Addition of the 5' cap

Addition of the poly-A tail

Exporting the transcript to the ribosome

Correct answer:

The removal of introns

Explanation:

snRNPs, or small nuclear ribonucleoproteins, are an essential part of the spliceosome complex. The spliceosome is responsible for the removal of introns from the primary transcript.

Example Question #981 : Ap Biology

Which of the following is not an example of eukaryotic post-transcriptional modification?

Possible Answers:

The 3' end of the growing strand is cleaved

A methylguanosine cap is added to the 5' end

After splicing, the exons are rejoined to form a final mRNA transcript

Exons, or non-coding regions, are removed via splicing

A poly-A tail is added to the 3' end

Correct answer:

Exons, or non-coding regions, are removed via splicing

Explanation:

Post-transcriptional modifications are changes that are made to the mRNA transcript before it is translated into a protein. The first of these changes is cleavage at the 3' end to separate the new strand, or "primary transcript," from the transcription machinery. Next, a protective 5' cap is added, as is a string of adenine nucleotides at the 3' end. Finally, noncoding regions, called introns, are spliced out and the exons, or coding regions, are reconnected.

The incorrect statement confuses exons and introns.

Example Question #982 : Ap Biology

Which of the following choices is not one of the processes associated with post-transcriptional modification?

Possible Answers:

Polyadenylation

Splicing

Protein folding

5' capping

Correct answer:

Protein folding

Explanation:

Post-transcriptional modification is the stage where the recently synthesized primary RNA transcript undergoes changes to become a mature RNA molecule. Post-transcriptional modifications ensure that the correct RNA transcripts are produced and that the correct proteins are translated. Post-transcriptional modification includes the processes of polyadenylation, 5’ capping, and splicing. Polyadenylation is the addition of adenine bases (the poly-A tail) to the 3’ end of the RNA primary transcript. The poly-A tail is important in export, stability, and translation of the transcript. 5’ capping is the addition of guanine bases to the 5’ end of the primary transcript. The 5’ cap aids in export and translation of the transcript and also protects it from degradation. Splicing is the removal of non-coding regions, or introns, from the primary transcript.

Example Question #1 : Understanding Post Transcription Modification

Which of the following choices is not a true characteristic of spliceosomes?

Possible Answers:

They splice introns from primary RNA transcripts

Most spliceosomes are found in the nucleus

They are composed of small nuclear RNA molecules (snRNAs)

Both prokaryotes and eukaryotes have spliceosomes

Correct answer:

Both prokaryotes and eukaryotes have spliceosomes

Explanation:

The spliceosome is a complex structure composed of small nuclear RNA molecules (snRNAs) and other proteins. They are often located in the nucleus. The spliceosome splices introns from the primary RNA transcript. This process occurs through splicing at 5’ and 3’ sites that are identified by particular nucleotide sequences. Prokaryotic cells do not contain spliceosomes. 

Example Question #2 : Understanding Post Transcription Modification

Which statement correctly describes the process of alternative splicing?

Possible Answers:

Alternative splicing can create a variety of proteins from the same primary transcript

In alternative splicing, some primary RNA transcripts are spliced and others are not

There are different methods of alternative splicing (spliceosomes, self-splicing, etc.)

There are different alternative splicing processes between prokaryotes and eukaryotes

Correct answer:

Alternative splicing can create a variety of proteins from the same primary transcript

Explanation:

Alternative splicing is the process where many different proteins can be formed from a primary transcript. This can be done in a number of ways, including using different splice sites, maintaining introns, and splicing out exons. Alternative splicing is an important process because it increases cellular efficiency; if many proteins can result from the same primary transcript, then the genome doesn’t need to code for as many unique transcripts.

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