Biochemistry : Nucleic Acid Synthesis

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #9 : Transcription

Which of the following is a ribozyme?

Possible Answers:

RNase H

RNA polymerase II

All of these are ribozymes

Guanyltransferase

RNase P

Correct answer:

RNase P

Explanation:

RNase H is involved in reverse transcriptase, but it is not a ribozyme. RNase P is a ribonuclease that cleaves/processes rRNA and generates 5' ends. The RNA component of RNase P is its catalytic subunit.

Example Question #31 : Nucleic Acid Synthesis

Within a eukaryotic chromosome, which of the following pairs of processes can occur at the same time?

Possible Answers:

Replication and splicing

Transcription and translation

Transcription and splicing

Translation and splicing

Replication and transcription

Correct answer:

Transcription and splicing

Explanation:

In eukaryotes, transcription and splicing could occur simultaneously. Both of these processes take place in the nucleus of the cell, while translation takes place in the cytoplasm. Therefore, translation could not happen at the same time as either transcription or splicing. Replication occurs totally independently from all of the other processes listed.

Example Question #51 : Anabolic Pathways And Synthesis

Oftentimes, biochemists say that the genetic code is degenerate. What are they referring to when they say this?

Possible Answers:

The sequence of one type of molecule is able to code for the sequence of another type of molecule

The same genetic code is not shared by all species

A change in the reading frame alters expression of all subsequent codons

Some codons are able to code for more than just one amino acid

Some amino acids can be coded for by more than just one codon

Correct answer:

Some amino acids can be coded for by more than just one codon

Explanation:

While some of these answer choices are true, others are false. But even for the choices that are true, only one of them directly answers the question. Let's go ahead and look at each choice.

  • Some amino acids can be coded for by more than just one codon

This is a true statement, and is also the correct answer. The degeneracy of the code is due to the fact that, for some amino acids, a number of different codons can result in the same amino acid. For example, the amino acid tyrosine can be coded for by either UAU or by UAC.

  • A change in the reading frame alters expression of all subsequent codons

While this is a true statement, it does not answer the question. Nonetheless, it's important to know that mutations which either insert or delete a nucleotide will change the entire rest of the reading frame. Consequently, there are likely to be many errors and the resultant polypeptide will likely not be functional.

  • Some codons are able to code for more than just one amino acid

This is a false statement. But be careful. This answer choice looks a lot like the correct one. The difference is that, for this choice, we're talking about a single codon being able to code for more than one amino acid. This is not the case.

  • The sequence of one type of molecule is able to code for the sequence of another type of molecule

This is a true statement with regards to gene expression. For transcription, the DNA (sequence of deoxyribonucleotides) serves as a template for the formation of mRNA (sequence of ribonucleotides). And for translation, that same mRNA serves as a precursor for the formation of a polypeptide (sequence of amino acids).

  • The same genetic code is not shared by all species

From what we know, this is a false statement. The genetic code is universal, meaning that all living things have been found to have the same codon-amino acid relationship.

Example Question #52 : Anabolic Pathways And Synthesis

When biochemists says that genes can be in either direction of the DNA, what do they mean?

Possible Answers:

The template for transcription can be found on either strand of DNA

Genes can be found both in the middle and at ends of a chromosome

The different alleles for a given gene within chromosomes can be partitioned to either of two cells during mitosis

Genes can be transcribed in both directions, from  and 

Correct answer:

The template for transcription can be found on either strand of DNA

Explanation:

The saying that genes can run in either direction is referring to how they can be expressed. Genes can be found on either strand of the DNA molecule. Since these two strands run antiparallel to one another, the genes being read on one strand would be read in the opposite direction on the other strand.

Genes can also be located on various loci within a given chromosome. Also, it is true that genes assort independently during cell division, but this doesn't answer the question. Also, genes can only be read in the  direction. They can never be read in the  direction. This is because DNA polymerase, the enzyme responsible for elongating the chain, can only add nucleotides to a chain that has a hydroxyl group at the  position.

Example Question #31 : Nucleic Acid Synthesis

Reverse transcriptase is an enzyme that produces DNA molecules from RNA. Which of the following is correct? 

Possible Answers:

Retroviruses have this enzyme and use it to replicate their RNA genome

In eukaryotes reverse transcriptase is encoded by retrotransposons

Reverse transcriptase activity is present in DNA viruses

All of these

Telomerase (the enzyme that maintains telomere length in eukaryotes) has reverse transcriptase activity

Correct answer:

All of these

Explanation:

The reverse transcriptase activity of retroviruses like HIV is used to replicate their RNA genome in the host cell. This activity is not needed or present in DNA viruses which can use the host's  enzymes to replicate. The reverse transcriptase activity of telomerases is used to prevent telomere ends shortening after multiple replications in somatic cells. Telomeres are short sequences at the end of chromosomes that prevent deterioration of the chromosomes. Retrotransposones are elements that amplify repetitive sequences in the DNA of eukaryotes.

Example Question #32 : Nucleic Acid Synthesis

What is the name of the process in which RNA is converted to DNA?

Possible Answers:

Replication

Reverse translation

Translation

Transcription

Reverse transcription

Correct answer:

Reverse transcription

Explanation:

For biochemical purposes, it is important to have an understanding of the "Central Dogma" of molecular biology. DNA multiplies via replication, is turned into RNA via transcription, and finally to proteins via translation. Going back to DNA from RNA is known as reverse transcription, and is the correct answer. The term "reverse translation" can refer to an aspect of cloning, but does not naturally occur.

Example Question #33 : Nucleic Acid Synthesis

Which of the following matches is correct regarding eukaryotic termination of transcription?

Possible Answers:

The mRNA cap is added to the 3' end of mRNA

The mRNA cap and the Poly A tail are added to the 3' end of mRNA

The mRNA cap and the poly A tail are added to the 5' end of mRNA

The poly A tail is added to the 3' end of mRNA

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

Correct answer:

The poly A tail is added to the 3' end of mRNA

Explanation:

After transcription, mRNA is modified so that it can be preserved for a longer time in the cell. A nucleotide cap structure is attached to the 5' end of the mRNA and a poly A tail is attached to the 3' end of the mRNA in order to accomplish this goal.

Example Question #34 : Nucleic Acid Synthesis

What is the likely genetic make-up of a virus which contains a RNA-dependent RNA polymerase?

Possible Answers:

Single-stranded DNA

Minus-strand RNA

Plus-strand RNA

Double-stranded RNA

Double-stranded DNA

Correct answer:

Minus-strand RNA

Explanation:

We're given the type of enzyme contained within a virus, and we're asked to make a determination of the virus' genetic makeup.

To begin with, we're told that the enzyme is an RNA-dependent RNA polymerase. The name of the enzyme gives us insight into what it does. It requires RNA as a template to produce more RNA.

So if this enzyme can convert RNA into RNA, where does the original RNA come from? The answer is that it must come from the virus. This means that we must be dealing with single-stranded RNA.

Now, the question is to determine the sense of the RNA genome of the virus. That is to say, it can be minus or plus. A minus-sense RNA is one whose complementary sequence can be translated into protein. A plus-sense RNA is one that doesn't need any processing to be translated. Rather, plus-sense RNA can be translated right away. Since we know that the enzyme present is going to produce RNA from RNA, we can then reason that the viral genome is likely minus-sense. When the minus-sense RNA is enacted on by this enzyme, the result is a new strand of RNA that can be translated into protein to serve the needs of the virus.

Example Question #35 : Nucleic Acid Synthesis

What is the relationship of the RNA transcript to the DNA template strand?

I. The RNA transcript is antiparallel to the DNA template strand.

II. The RNA transcript is complementary to the DNA template strand. 

III. The RNA transcript is identical to the DNA template strand.

IV. In the RNA transcript, thymine is replaced with uracil.

Possible Answers:

I, II, and IV

I, II, and III

I and II

I, III, and IV

I and IV

Correct answer:

I, II, and IV

Explanation:

The RNA transcript contains nucleotide bases at each position, which are complementary to the DNA. RNA is synthesized in the 5' to 3' direction from a DNA template strand with antiparallel direction (3' to 5').The coding DNA strand is identical to the RNA transcript with the exception that thymine is replaced with uracil in RNA. 

Example Question #36 : Nucleic Acid Synthesis

How does initiation of transcription occur in eukaryotes?

I. In eukaryotes sigma protein factor is not required for transcription to occur.

II. Transcription factors such as TFIID bind and activate the gene promoter.

III. RNA polymerase II recognizes and binds the promoter of the gene to be transcribed.

 

Possible Answers:

I and II

II and III

I only

I, II, and III

III only

Correct answer:

I, II, and III

Explanation:

Eukaryotes have three types of RNA polymerase, I, II, and III. RNA polymerase II recognizes the promoter and binds to the promoter forming a preinitiation complex. The polymerase is composed of 10-12 subunits. Transcription factors also bind the promoter (the region of DNA upstream of the start or origin of transcription).In eukaryotes sigma protein factor is not required for transcription to occur.

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