Question 1

Although DNA is the main hereditary material in all life-forms,it lacks one important characteristic of being a candidate for the first life-form.Why have researchers rejected the idea that DNA was found in the first life-form?

Accepted Answer

DNA does not function as a catalyst, which is a crucial characteristic for the first life-form to facilitate chemical reactions necessary for life processes. RNA, on the other hand, can act as a catalyst and is considered a more likely candidate for the first life-form.

Question 2

Use the following information when answering the corresponding question(s).
Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme)from hepatitis delta virus catalyzes self-cleavage of a ...[chemical] ...bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme.The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge.Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid,and magnesium hydroxide acting as the base.Specifically,the cytosine donates its proton (H⁺)to neutralize the unstable negative charge that would have formed on the ribozyme.
-Refer to Nakano's quote from Science.If the cytosine is positively charged (+)before self-cleavage,what would its charge be after self-cleavage?

Accepted Answer

The answer of Use the following information when answering the...

Question 3

Which one of the following is not a way that RNA is seen as intermediate between DNA and proteins?

Accepted Answer

RNA may have 5' and 3' termini like DNA, but it does not have amino and carboxy termini like proteins. The amino and carboxy termini are specific to proteins and are involved in their folding and function.

Question 4

Which of the following is a difference between RNA and DNA?

Accepted Answer

The answer of Which of the following is a difference...

Question 5

Use the following information when answering the corresponding question(s).
Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme)from hepatitis delta virus catalyzes self-cleavage of a ...[chemical] ...bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme.The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge.Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid,and magnesium hydroxide acting as the base.Specifically,the cytosine donates its proton (H⁺)to neutralize the unstable negative charge that would have formed on the ribozyme.
-Which of the following chemical bonds do you think Nakano is referring to in his quote?

Accepted Answer

Nakano specifically mentions a self-cleavage reaction, which refers to the breaking of a phosphodiester bond between two nucleotides in an RNA molecule. The other choices (A, B, and D) refer to different types of chemical bonds that are not relevant to RNA self-cleavage.

Question 6

Use the following information when answering the corresponding question(s).
Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme)from hepatitis delta virus catalyzes self-cleavage of a ...[chemical] ...bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme.The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge.Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid,and magnesium hydroxide acting as the base.Specifically,the cytosine donates its proton (H⁺)to neutralize the unstable negative charge that would have formed on the ribozyme.
-Is Nakano's quote from Science consistent with the textbook's claim that RNA is a good candidate for the first life-form?

Accepted Answer

Nakano's report provides evidence that RNA, a component of the hepatitis delta virus, can catalyze self-cleavage reactions and can be involved in acid-base reactions. This supports the idea that RNA is a versatile molecule capable of performing multiple functions, making it a strong candidate for the first life-form.

Question 7

You isolate what you think is DNA from a tissue sample.Which of the following will verify that you do,indeed,have DNA (rather than some other type of molecule)?

Accepted Answer

None of the options A-C are definitive for identifying DNA. Carbon-carbon bonds and primary/secondary structures are common in many biomolecules, and while DNA contains nitrogen and phosphorus, so do other molecules like RNA. Specific tests, such as DNA sequencing or PCR, are needed to confirm DNA.

Question 8

Why do researchers think the first self-replicating molecule was RNA?

Accepted Answer

RNA has the capacity to provide a template and is known to catalyze reactions. Although no existing self-replicating molecules of RNA have been discovered, it is currently the most likely candidate for the first self-replicating molecule due to its properties.

Question 9

Use the following information when answering the corresponding question(s).
Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme)from hepatitis delta virus catalyzes self-cleavage of a ...[chemical] ...bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme.The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge.Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid,and magnesium hydroxide acting as the base.Specifically,the cytosine donates its proton (H⁺)to neutralize the unstable negative charge that would have formed on the ribozyme.
-Refer to Nakano's quote.What can be inferred about the free-energy profile for the self-cleavage reaction from the information provided in the paragraph?

Accepted Answer

The fact that the RNA enzyme catalyzes self-cleavage suggests that it is energetically favorable, which would correspond to an exergonic reaction. The information provided does not suggest anything about whether the reaction is endothermic or exothermic.

Question 10

The work of Bartel's group on the ribozyme RNA replicase supports which conclusion?

Accepted Answer

Bartel's group demonstrated that a ribozyme RNA replicase could catalyze the replication of RNA, supporting the idea of an RNA world where self-replicating RNA molecules could have been the precursors to life as we know it. This discovery does not support options B, C, or D.

Question 11

Bartel's research group showed that an RNA replicase ribozyme could be created by _____.

Accepted Answer

Bartel's research group used an evolutionary approach to create the RNA replicase ribozyme. They started with random RNA components and allowed selection to result in molecules that were better and better at replicating. This approach is known as in vitro evolution or directed evolution.

Question 12

Recall the Bartel lab group experiment to create a ribozyme from scratch.If they had created exact copies of each ribozyme (rather than creating copies with a few differences),what would have been the most likely result?

Accepted Answer

If exact copies of each ribozyme were created, there would not be any room for variability or mutations. Therefore, the ribozymes would stay the same with each round of selection, as there would not be any natural selection occurring due to changes in the ribozymes.

Question 13

Use the following information when answering the corresponding question(s).
Shu-ichi Nakano reported in Science in February 2000 that "The RNA enzyme (ribozyme)from hepatitis delta virus catalyzes self-cleavage of a ...[chemical] ...bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme.The author goes on to show that this self-cleavage is made faster by joining it with an acid-base reaction that neutralizes the negative charge.Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid,and magnesium hydroxide acting as the base.Specifically,the cytosine donates its proton (H⁺)to neutralize the unstable negative charge that would have formed on the ribozyme.
-In the acid-base reaction described in the preceding paragraph about Nakano's research on RNAs,a proton (H⁺)is being transferred.What is acting as the proton acceptor?

Accepted Answer

Magnesium hydroxide is acting as the base in the acid-base reaction and is accepting the proton (H⁺) from the ribozyme's cytosine base.

Quiz 4: Nucleic Acids and the Rna World