Question 1

One of the primary functions of RNA molecules is to ________.
A) transmit genetic information to offspring
B) function in the synthesis of proteins
C) make a copy of itself, thus ensuring genetic continuity
D) act as a pattern or blueprint to form DNA
E) form the genes of higher organisms

Accepted Answer

RNA molecules function in the synthesis of proteins by carrying genetic information from DNA to the ribosomes, where protein synthesis occurs. This process is known as transcription and translation. While RNA can make a copy of itself, this is not one of its primary functions, and it does not form the genes of higher organisms. The transmission of genetic information to offspring is primarily the function of DNA. RNA does not act as a pattern or blueprint to form DNA.

Question 2

Which of the following best describes DNA's secondary structure?
A) beta-pleated sheet
B) double parallel helical strands
C) turn-loop-turn
D) double antiparallel helical strands

Accepted Answer

DNA's secondary structure consists of a double antiparallel helix where the two strands run in opposite directions. This structure allows for complementary base pairing, which is crucial for DNA replication and gene expression. Options A, B, and C are describing the secondary structures of proteins, not DNA.

Question 3

Compare proteins to nucleic acids. Which of the following is TRUE?
A) Both have primary and secondary structure.
B) Both contain sulfur.
C) Both are used as templates to synthesize polymers
D) Both have monomers, which contain phosphorus.

Accepted Answer

Both proteins and nucleic acids have primary structure (amino acid sequence in proteins and nucleotide sequence in nucleic acids) and secondary structure (alpha helices, beta sheets, etc. in proteins and base pairing in nucleic acids). Option B is incorrect since only proteins contain sulfur (due to presence of cysteine amino acid). Option C is partially correct as nucleic acids are used as templates for DNA replication and RNA transcription, while proteins serve as templates for protein synthesis. Option D is also incorrect as nucleic acid monomers (nucleotides) contain phosphorus, while protein monomers (amino acids) do not.

Question 4

Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of ________.
A) purines is always larger than the number of pyrimidines
B) pyrimidines is always larger than purines
C) cytosines is always the same as adenines
D) guanines is always the same as thymines
E) purines is always the same as pyrimidines

Accepted Answer

Watson and Crick already knew that the number of purines (adenine and guanine) was equal to the number of pyrimidines (cytosine and thymine) in DNA. This knowledge was crucial in determining the structure of DNA, as it allowed them to deduce that the nitrogenous bases must pair up in a complementary fashion (adenine with thymine and cytosine with guanine).

Question 5

Which of the following statements about the 5' end of a polynucleotide strand of RNA is correct?
A) The 5' end has a hydroxyl group attached to the number 5 carbon of ribose.
B) The 5' end has a phosphate group attached to the number 5 carbon of ribose.
C) The 5' end has phosphate attached to the number 5 carbon of the nitrogenous base.
D) The 5' end has a carboxyl group attached to the number 5 carbon of ribose.
E) The 5' end is the fifth position on one of the nitrogenous bases.

Accepted Answer

The 5' end of RNA has a phosphate group attached to the number 5 carbon of ribose. This is important in forming phosphodiester bonds between nucleotides in the RNA strand.

Question 6

If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?
A) phospholipids
B) DNA
C) RNA
D) both DNA and RNA
E) proteins

Accepted Answer

Uracil is a nitrogenous base that is found in RNA, but not in DNA. Therefore, if 14C-labeled uracil is added to the growth medium of cells, it will label RNA. However, since RNA is involved in the synthesis of DNA, the labeled uracil may also be incorporated into newly synthesized DNA, depending on the stage of the cell cycle. Therefore, both RNA and DNA can potentially be labeled with 14C-labeled uracil. The other options (A, B, and E) are incorrect, as they do not contain uracil or are not synthesized using uracil.

Question 7

Why do researchers think the first self-replicating molecule was RNA?
A) RNA is the only type of molecule that can catalyze a chemical reaction.
B) RNA can carry information and catalyze chemical reactions.
C) Self-replicating molecules of RNA exist today, in human cells.
D) Fossil evidence of such a molecule was recently discovered.

Accepted Answer

RNA is believed to have been the first self-replicating molecule because it is capable of both carrying information and catalyzing chemical reactions. This property allows RNA to act both as a template for copying genetic information and as an enzyme to speed up the reactions necessary for replication. Although self-replicating RNA molecules do exist today in some living organisms, this is not the primary reason why researchers believe RNA was the first self-replicating molecule. There is no fossil evidence of such a molecule that has been discovered so far. Finally, choice A is incorrect because there are other types of molecules, such as certain proteins, that can also catalyze chemical reactions.

Question 8

DNA is the main hereditary material of all life. However, DNA lacks one important characteristic for the first forms of life. Why have researchers rejected the idea that DNA was found in the first life-form?
A) It does not function as a catalyst.
B) It is not stable enough to have withstood early Earth's harsh atmosphere.
C) DNA only has four types of bases. Therefore, DNA cannot adapt and evolve.
D) The type of sugar found in DNA is too complicated to have been present early in Earth's history.

Accepted Answer

DNA does not have catalytic properties, which are necessary for the biochemical reactions required for life. RNA, which can act as both genetic material and a catalyst, is thought to have been the first hereditary material.

Question 9

A double-stranded DNA molecule contains a total of 120 purines and 120 pyrimidines. This DNA molecule could be composed of ________.
A) 120 adenine and 120 uracil molecules
B) 120 thymine and 120 adenine molecules
C) 120 cytosine and 120 thymine molecules
D) 120 adenine and 120 cytosine molecules
E) 120 guanine and 120 thymine molecules

Accepted Answer

In a double-stranded DNA molecule, the number of purines (adenine and guanine) is equal to the number of pyrimidines (cytosine and thymine) due to base pairing rules (A pairs with T, and C pairs with G). Option B correctly reflects this pairing, with 120 adenine molecules pairing with 120 thymine molecules.

Question 10

Both DNA and RNA ________.
A) are information-containing molecules
B) show primary, secondary, tertiary, and quaternary structure
C) are highly reactive catalysts in cells
D) naturally occur as a double helix

Accepted Answer

Both DNA and RNA are information-containing molecules that store genetic information in cells. Although RNA can have secondary structure, it does not have tertiary or quaternary structure, and neither DNA nor RNA are reactive catalysts in cells. While DNA naturally occurs as a double helix, RNA typically adopts a single-stranded structure.

Question 11

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), the ribozymes would have ________.
A) become more efficient with each round of selection
B) stayed the same with each round of selection
C) become less efficient with each round of selection
D) stopped catalyzing reactions after just a few rounds of selection

Accepted Answer

If they had created exact copies of each ribozyme, the ribozymes would have stayed the same with each round of selection. This is because there would be no variation for natural selection to act on, and therefore no improvements could be made.

Question 12

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?
A) 5'-purine-pyrimidine-purine-pyrimidine-3' with 3'-purine-pyrimidine-purine-pyrimidine-5'
B) 5'-AGCT-3' with 5'-TCGA-3'
C) 5'-GCGC-3' with 5'-TATA-3'
D) 5'-ATGC-3' with 5'-GCAT-3'
E) All of these pairs are correct.

Accepted Answer

The structure of DNA is based on complementary base pairing between purines and pyrimidines. Adenine (A) always pairs with thymine (T), while guanine (G) always pairs with cytosine (C). Therefore, the only option in which the bases follow this rule is Option D, where adenine pairs with thymine and guanine pairs with cytosine in both sequences. Option A has purines on both strands, which means they cannot base-pair according to the rules of DNA structure. Option B has mismatched base pairs, with A on one strand pairing with T on the other and G on one strand pairing with C on the other. Option C also has mismatched base pairs, with G and C not pairing with each other. Therefore, the correct answer is D.

Question 13

If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence ________.
A) 5'TAACGT3'
B) 5'TGCAAT3'
C) 5'UAACGU3'
D) 3'UAACGU5'
E) 5'UGCAAU3'

Accepted Answer

The complementary strand of DNA always pairs in a specific way; adenine (A) with thymine (T), and guanine (G) with cytosine (C). Therefore, the complementary strand of 5'ATTGCA3' would be 5'TGCAAT3'.

Question 14

Why is it that RNA can catalyze reactions but DNA cannot?
A) The sugar of RNA is much more reactive than the sugar of DNA.
B) The bases of RNA are much more reactive than the bases of DNA.
C) The phosphate groups of RNA are much more reactive than the phosphate groups of DNA.
D) The primary structure of RNA is fundamentally different than the primary structure of DNA.

Accepted Answer

The sugar of RNA (ribose) contains a reactive hydroxyl group (-OH) on the 2' carbon, which can participate in catalytic reactions. In contrast, the sugar of DNA (deoxyribose) lacks this hydroxyl group, making it less reactive and unable to catalyze reactions.

Question 15

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes?
A) The two strands of the double helix would separate.
B) The phosphodiester linkages of the polynucleotide backbone would be broken.
C) The purines would be separated from the deoxyribose sugars.
D) The pyrimidines would be separated from the deoxyribose sugars.
E) All bases would be separated from the deoxyribose sugars.

Accepted Answer

Enzymes that break down DNA catalyze the hydrolysis of the phosphodiester linkages that join nucleotides together. This results in the breaking apart of the sugar-phosphate backbone of the DNA molecule. The two strands of the double helix would separate as a result of this. Choice A is partly correct in that the separation of the strands will occur, but it is not the primary effect of the enzyme treatment. Choices C, D, and E are incorrect as they describe the separation of individual components of nucleotides rather than the breaking of covalent bonds between them.

Question 16

RNA and proteins combine in cells to form structures called ribosomes. Ribosomes contain the active site for peptide bond formation. Based on their chemical structures, do you think protein or RNA molecules actually form the active site within the ribosome?
A) protein, because RNA cannot catalyze reactions
B) RNA, because proteins cannot catalyze a reaction that involves another protein
C) proteins, because only proteins can catalyze a reaction that involves another protein
D) It could be either, because both molecules have catalytic properties.

Accepted Answer

Both proteins and RNA molecules have catalytic properties, and either could form the active site within the ribosome.

Question 17

Which of the following statements best summarizes the differences between DNA and RNA?
A) DNA encodes hereditary information, whereas RNA does not.
B) The bases in DNA contain sugars, whereas the bases in RNA do not contain sugar.
C) DNA nucleotides contain a different sugar than RNA nucleotides.
D) DNA contains the base uracil, whereas RNA contains the base thymine.
E) The bases in DNA contain sulfur, whereas the bases in RNA do not contain sulfur.

Accepted Answer

The main difference between DNA and RNA is that the sugar molecule in DNA is deoxyribose, while in RNA it is ribose. This means that DNA nucleotides contain a different sugar than RNA nucleotides. The other options are incorrect: A is incorrect because RNA also carries genetic information; B is incorrect because the bases in RNA do indeed contain sugar; D is incorrect because DNA contains thymine, whereas RNA contains uracil; E is incorrect because neither DNA nor RNA contains sulfur in their bases.

Question 18

In the context of chemical evolution, DNA's structure is interesting because it suggests a possible copying mechanism. What about DNA's structure facilitates copying?
A) It has the same number of purines and pyrimidines.
B) The nitrogenous bases are located on the inside of the double helix.
C) The strands of the double helix are complementary.
D) DNA always goes from 5 prime to 3 prime.

Accepted Answer

The complementary base pairing of the two strands of DNA allows for accurate and efficient copying. As each strand acts as a template for the formation of a new strand, the base pairing rules ensure that the new strand is complementary to the original. This results in two identical copies of the original DNA molecule.

Question 19

Franklin and Wilkins analyzed DNA by bombarding DNA crystals with X-rays. Their analysis yielded two numbers that sparked interest, 3.4 nm and 0.34 nm. What is the significance of these numbers?
A) It turned out to be just a coincidence.
B) DNA molecules are 3.4 nm long and 0.34 nm wide.
C) The width of a DNA molecule is 3.4 nm, whereas the width of a nucleotide monomer is 0.34 m.
D) These numbers demonstrate there are 10 rungs, or steps, on the DNA "ladder" for every turn of the helix.
E) The 10 to 1 ratio signifies that DNA molecules are 10 times longer than they are wide.

Accepted Answer

The 3.4 nm represents the length of one complete turn of the DNA helix, while 0.34 nm is the distance between adjacent base pairs. This means there are 10 base pairs (or "rungs") in each complete turn of the helix.

Question 20

What is the structural feature that allows DNA to replicate?
A) sugar-phosphate backbone
B) complementary pairing of the nitrogenous bases
C) disulfide bonding (bridging) of the two helixes
D) twisting of the molecule to form an α-helix
E) three-component structure of the nucleotides

Accepted Answer

The complementary pairing of the nitrogenous bases (adenine with thymine, and guanine with cytosine) is what allows DNA to replicate. During replication, the double helix molecule unravels and each strand serves as a template for the synthesis of a new, complementary strand. The base pairing rules ensure that the new strand is an exact copy of the original.

Quiz 4: Nucleic Acids and the Rna World

One of the primary functions of RNA molecules is to ________.

Which of the following best describes DNA's secondary structure?

Compare proteins to nucleic acids. Which of the following is TRUE?

Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of ________.

Which of the following statements about the 5' end of a polynucleotide strand of RNA is correct?

If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?

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

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

A double-stranded DNA molecule contains a total of 120 purines and 120 pyrimidines. This DNA molecule could be composed of ________.

Both DNA and RNA ________.

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) , the ribozymes would have ________.

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?

If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence ________.

Why is it that RNA can catalyze reactions but DNA cannot?

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes?

RNA and proteins combine in cells to form structures called ribosomes. Ribosomes contain the active site for peptide bond formation. Based on their chemical structures, do you think protein or RNA molecules actually form the active site within the ribosome?

Which of the following statements best summarizes the differences between DNA and RNA?

In the context of chemical evolution, DNA's structure is interesting because it suggests a possible copying mechanism. What about DNA's structure facilitates copying?

Franklin and Wilkins analyzed DNA by bombarding DNA crystals with X-rays. Their analysis yielded two numbers that sparked interest, 3.4 nm and 0.34 nm. What is the significance of these numbers?

What is the structural feature that allows DNA to replicate?