SAT II Biology E : Molecular Biology

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

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Example Questions

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Example Question #74 : Sat Subject Test In Biology

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:

tRNA molecules would not recognize ribosomal binding sites.

DNA transcription would not be able to proceed.

All of these

Amino acids would not bind to tRNA molecules.

The tRNA reserves in the cell would eventually be depleted.

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 #75 : Sat Subject Test In Biology

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:

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

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 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.

All of these

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.

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 #76 : Sat Subject Test In Biology

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

Possible Answers:

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 uses uracil nucleotides instead of thymine nucleotides.

All of these

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

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 #51 : Molecular Biology

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

Possible Answers:

None of these

mRNA, tRNA, and rRNA

tRNA, rRNA, and miRNA

miRNA, rRNA, and snRNA

mRNA, snRNA, and rRNA

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 #78 : Sat Subject Test In Biology

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

Possible Answers:

tRNA

snRNA

rRNA

mRNA

DNA

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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