SAT II Biology M : RNA Structure and Function

Study concepts, example questions & explanations for SAT II Biology M

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Example Questions

Example Question #1 : Rna Structure And Function

In terms of histone modification, what will result in a greater rate of gene expression?

Possible Answers:

Addition of 5' Terminal Cap

Histone acetylation

DNA methylation 

Addition of 3' Poly A Tail

Alternative RNA splicing

Correct answer:

Histone acetylation

Explanation:

Histone acetylation is the process of adding acetyl groups to positively charged lysine groups of histones. This process loosens the histone which allows for an easier initiation of transcription, which will lead to greater gene expression. DNA methylation does the opposite by adding methyl groups to DNA and lowering the rate of transcription. Alternative RNA splicing deals with RNA having certain introns and exons spliced out in a manner that produces different strands of mRNA from the same template strand of RNA. Addition of 5’ Terminal Cap and the addition of 3’ Poly A Tail relate to gene expression in that they both have to do with creating mature mRNA that is ready for translation into protein.

Example Question #2 : Rna Structure And Function

You find a specialized type of RNA in the nucleus but nowhere else in the cell, including the cytoplasm. What type of RNA is it?

Possible Answers:

mRNA

snRNA

tRNA

rRNA

scRNA

Correct answer:

snRNA

Explanation:

mRNA will be found in both the nucleus and in the cytoplasm because it is transcribed from DNA in the nucleus and then exported to the cytoplasm to go through translation. tRNA will be found in the cytoplasm because it is an integral part of translation in that it delivers amino acids to the ribosome. rRNA will also be found in the cytoplasm because it couples with ribosomal proteins to make up the ribosomes found in the cytoplasm. scRNA is also known as small cytoplasmic RNA and has a function that is still not very well known, but they are mostly only found in the cytoplasm. snRNA, or small nuclear RNA, are only found in the nucleus and are an integral part of splicing introns of RNA so it can go onto becoming mRNA.

Example Question #2 : Rna Structure And Function

Suppose a mutation in an organism's genome produces a malformed version of tRNA synthetase. This malformed version of the enzyme is completely non-functional. What would be the direct effect on the cell producing non-functional tRNA synthetase?

Possible Answers:

Amino acids would not bind to tRNA molecules.

The tRNA reserves in the cell would eventually be depleted.

All of these

DNA transcription would not be able to proceed.

tRNA molecules would not recognize ribosomal binding sites.

Correct answer:

Amino acids would not bind to tRNA molecules.

Explanation:

tRNA synthetase plays a vital role in translation, but not transcription. tRNA synthetase is the enzyme that binds specific amino acids to corresponding tRNA molecules, and then the tRNA molecules transport the amino acids to the ribosome to create a polypeptide. tRNA molecules are not consumed in this process, and tRNA reserves will not be depleted if tRNA synthetase were non-functional.

Example Question #3 : Rna Structure And Function

Eukaryotic cells are able to modify the primary mRNA transcript in a number of different ways. Which of the following answer choices is an advantage of post-transcriptional modification?

Possible Answers:

All of these

The primary transcript can be modified by a spliceosome, which can remove the mRNA's exons and shuffle the introns in a way that can produce multiple different protein products.

The primary transcript can be modified by a spliceosome, which can remove the mRNA's introns and shuffle the exons in a way that can produce multiple different protein products.

The 5' poly-A tail and 3' methyl cap help the mRNA transcript find and bind to the ribosome, and as such increase speed of translation.

The 5' poly-A tail and 3' methyl cap help resist degradation of the mRNA transcript.

Correct answer:

The primary transcript can be modified by a spliceosome, which can remove the mRNA's introns and shuffle the exons in a way that can produce multiple different protein products.

Explanation:

Post-transcriptional modification is very beneficial to eukaryotic cells, especially because spliceosomes allow for one primary mRNA transcript to code for multiple different proteins. During this modification, introns are removed from the mRNA transcript, and the exons (remaining segments of mRNA) are shuffled around into the order that creates the protein the cell needs at the moment. While the poly-A tail and methyl cap are also very useful, the poly-A tail is on the 3' end, and the methyl cap is on the 5' end.

Example Question #4 : Rna Structure And Function

Which of the following answer choices describes a difference between DNA and RNA?

Possible Answers:

All of these

In eukaryotes, RNA is created from a DNA template.

RNA exists almost exclusively as a single stranded nucleic acid, while DNA generally is double stranded.

RNA has a main sugar of ribose while DNA has a main sugar of deoxyribose

RNA uses uracil nucleotides instead of thymine nucleotides.

Correct answer:

All of these

Explanation:

There are generally considered to be three major differences between DNA and RNA. 1) DNA has a main sugar of deoxyribose and RNA has a main sugar of ribose, 2) RNA uses uracil instead of thymine, and 3) RNA is almost exclusively a single-stranded nucleic acid. Further, DNA is generally the template that an organism uses to create RNA (except in specific organisms which use reverse transcriptase and use RNA to create DNA).

Example Question #5 : Rna Structure And Function

What are the three types of RNA most important to polypeptide formation? 

Possible Answers:

miRNA, rRNA, and snRNA

tRNA, rRNA, and miRNA

mRNA, tRNA, and rRNA

mRNA, snRNA, and rRNA

None of these

Correct answer:

mRNA, tRNA, and rRNA

Explanation:

The main three types of RNA necessary to create a polypeptide are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). snRNA is also important and can help modify the primary mRNA transcript, but it is only found in eukaryotes and is not absolutely essential to polypeptide formation. Micro RNA (miRNA) is also useful for post-transcriptional modification, but plays a minor role when compared to mRNA/tRNA/rRNA.

Example Question #6 : Rna Structure And Function

Which of the following nucleic acid types encodes the amino acid sequence of a polypeptide?

Possible Answers:

mRNA

rRNA

DNA

snRNA

tRNA

Correct answer:

mRNA

Explanation:

mRNA, or messenger RNA, carries genetic information from DNA into a three-letter code that encodes the amino acid sequence of a polypeptide (protein).

DNA contains the genetic instructions for structure and development of living things and stores genetic information over the long term.

tRNA, or transfer RNA, brings amino acids to ribosomes during translation of RNA to protein.  

rRNA, or ribosomal RNA, is a component of ribosomes along with ribosomal proteins. Ribosomes are the cell organelles responsible for translating mRNA to protein.

snRNA, or small nuclear RNA, forms complexes with proteins used in RNA processing. snRNA is found only in eukaryotes.

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