Question 1

Increasing the ion concentration increases the T_m because the ions A) bind to the phosphate groups of the DNA backbone and increase stability. B) bind to the nucleic acids and disrupt the base pairs, decreasing stability. C) increase the base length of the DNA, increasing stability. D) associate with the ribose sugars, decreasing stability.

Accepted Answer

Increasing the ion concentration can stabilize the DNA double helix by shielding the negatively charged phosphate groups in the backbone. The ions bind to the phosphate groups and reduce repulsion between the negatively charged DNA strands, increasing stability.

Question 2

Which form(s) of DNA exhibit(s) a zigzag arrangement?
A) A-DNA
B) B-DNA
C) Z-DNA
D) A-DNA and B-DNA

Accepted Answer

Z-DNA exhibits a zigzag arrangement due to the alternating pattern of purines and pyrimidines in its structure. A-DNA and B-DNA have a more helical structure.

Question 3

The K⁺ion concentration in a DNA sample is increased from 50 mM to 100 mM. The T_m will A) remain the same. B) decrease. C) increase. D) vary unpredictably.

Accepted Answer

Increasing the K⁺ ion concentration stabilizes the DNA double helix by shielding the negative charges on the phosphate backbone, leading to an increase in the melting temperature (T_m).

Question 4

The DNA of a bacteria was isolated and it was determined that 15% of the DNA is composed of cytosine. What percentage of the DNA is guanine?
A) 15%
B) 30%
C) 35%
D) 70%

Accepted Answer

According to the base pairing rule, the amount of guanine (G) in the DNA will be equal to the amount of cytosine (C) because G pairs with C. Therefore, if 15% of the DNA is composed of cytosine, then 15% of it will also be composed of guanine.

Question 5

DNA strands are considered to be antiparallel. This means the
A) phosphodiester bonds run in the same direction.
B) phosphodiester bonds run in different directions.
C) base pairs form hydrogen bonds.
D) phosphate backbone is on the outside of the helix.

Accepted Answer

Antiparallel means that the two strands run in opposite directions, with one strand running 5' to 3' and the other running 3' to 5'. This results in the phosphodiester bonds running in different directions. Choice A is incorrect because phosphodiester bonds run in opposite directions. Choice C is not a defining feature of antiparallel DNA strands. Choice D is also incorrect as the phosphate backbone is on the outside of the helix in both parallel and antiparallel strands.

Question 6

When DNA is transcribed into RNA, the strand has the same base sequences as the RNA transcript.
A) antiparallel
B) parallel
C) coding
D) template

Accepted Answer

The answer of When DNA is transcribed into RNA, the...

Question 7

Which form(s) of DNA exhibit(s) a right-handed helical structure?
A) A-DNA
B) B-DNA
C) Z-DNA
D) A-DNA and B-DNA

Accepted Answer

A-DNA and B-DNA both exhibit a right-handed helical structure, while Z-DNA has a left-handed helix.

Question 8

When DNA is transcribed into RNA, the strand has the complementary sequence to the transcribed RNA.
A) antiparallel
B) parallel
C) coding
D) template

Accepted Answer

During transcription, the DNA strand serves as a template for RNA synthesis, meaning that the RNA sequence will be complementary to the DNA strand. Therefore, the best choice is D, "template."

Question 9

The ability to monitor the denaturation of DNA using absorbance is referred to as
A) annealing.
B) supercoiling.
C) melting temperature.
D) hyperchromic effect.

Accepted Answer

The answer of The ability to monitor the denaturation of...

Question 10

As DNA unwinds and denatures, absorbance is predicted to
A) remain the same.
B) decrease.
C) increase.
D) vary unpredictably.

Accepted Answer

As DNA unwinds and denatures, the absorbance at 260 nm (a common measurement wavelength for DNA) increases due to the reduction in base stacking interactions, a phenomenon known as hyperchromicity.

Question 11

The figure below shows part of the primary structure of DNA. Identify the nucleotide. 
A) A
B) B
C) C
D) D

Accepted Answer

The answer of The figure below shows part of the...

Question 12

The basic structure of DNA is a right-handed helix formed by two strands of DNA.
A) antiparallel
B) parallel
C) coding
D) template

Accepted Answer

The two strands of DNA are oriented in opposite directions, with one strand running in the 5' to 3' direction and the other running in the 3' to 5' direction. This is referred to as antiparallel. Choice B, parallel, is incorrect because the two strands run in opposite directions. Choices C and D, coding and template, refer to specific functions of DNA but do not describe the overall structure of the molecule.

Question 13

Predict the complementary strand of the following DNA sequence: 5 ^' -ATCTGAATCT-3 ^' A) 5 ^' -TCTAAGTCTA-3 ^' B) 5 ^' -TAGACTTAGA-3 ^' C) 5 ^' -ATCTGAATCT-3 ^' D) 5 ^' -AGATTCAGAT-3 ^'

Accepted Answer

The complementary strand of DNA is formed by pairing A with T and G with C, so the complementary sequence to 5'-ATCTGAATCT-3' is 5'-AGATTCAGAT-3'.

Question 14

The figure below shows part of the primary structure of DNA. Identify the nucleoside. 
A) A
B) B
C) C
D) D

Accepted Answer

The nucleoside is composed of a nitrogenous base (either adenine, guanine, cytosine or thymine) and a pentose sugar (either ribose or deoxyribose). In this case, the nitrogenous base is cytosine and the pentose sugar is deoxyribose, which is found in DNA (not RNA). Therefore, the correct choice is C.

Question 15

Chargaff's rule is that the amount of
A) A = G and the amount of C = T.
B) A = C = G = T.
C) A = T and the amount of C = G.
D) A = C and the amount of G = T.

Accepted Answer

Chargaff's rule states that the amount of adenine (A) in DNA will always be equal to the amount of thymine (T), and the amount of cytosine (C) will always be equal to the amount of guanine (G). Therefore, choice C is the correct answer as it states that A = T and C = G.

Question 16

How many base pairs per turn does B-DNA contain?
A) 10.0
B) 10.5
C) 11.0
D) 12.0

Accepted Answer

B-DNA contains 10.5 base pairs per turn.

Question 17

The DNA double helix is considered to be a structure.
A) primary
B) secondary
C) tertiary
D) quaternary

Accepted Answer

The DNA double helix is considered to be a secondary structure because it is formed from the base pairing between nucleotides on opposite strands. The primary structure of DNA is the linear sequence of nucleotides, while the tertiary and quaternary structures involve higher levels of folding and interactions between multiple molecules.

Question 18

The DNA of a bacteria was isolated and it was determined that 15% of the DNA is composed of cytosine. What percentage of the DNA is adenine?
A) 15%
B) 30%
C) 35%
D) 70%

Accepted Answer

In DNA, the percentage of adenine always equals the percentage of thymine and the percentage of cytosine always equals the percentage of guanine. Therefore, if 15% of the DNA is made up of cytosine, then the percentage of guanine is also 15%. That leaves 70% (100% - 15% - 15%) of the DNA to be composed of adenine and thymine, and since they are always equal to each other, adenine must make up 35% of the DNA.

Question 19

What is the melting temperature from the DNA absorbance shown in the figure below? 
A) 80 $\degree$C
B) 85 $\degree$C
C) 90 $\degree$C
D) 95 $\degree$C

Accepted Answer

The answer of What is the melting temperature from the...

Question 20

The interior stacking of the DNA bases in the double helix provides stability through
A) hydrophobic and van der Waals interactions.
B) hydrophilic and van der Waals interactions.
C) hydrophilic and ion-dipole interactions.
D) hydrophobic and ion-dipole interactions.

Accepted Answer

The interior stacking of the DNA bases in the double helix is stabilized by hydrophobic and van der Waals interactions. These interactions are due to the arrangement of the nitrogenous bases along the axis of the helix, creating a hydrophobic environment in the middle of the helix. The hydrogen bonds between the bases on opposite strands also contribute to the stability of the double helix, but they are not part of the interior stacking interactions.

Quiz 3: Nucleic Acid Structure and Function

Increasing the ion concentration increases the T_m because the ions

Which form(s) of DNA exhibit(s) a zigzag arrangement?

The K⁺ion concentration in a DNA sample is increased from 50 mM to 100 mM. The T_m will

The DNA of a bacteria was isolated and it was determined that 15% of the DNA is composed of cytosine. What percentage of the DNA is guanine?

DNA strands are considered to be antiparallel. This means the

When DNA is transcribed into RNA, the strand has the same base sequences as the RNA transcript.

Which form(s) of DNA exhibit(s) a right-handed helical structure?

When DNA is transcribed into RNA, the strand has the complementary sequence to the transcribed RNA.

The ability to monitor the denaturation of DNA using absorbance is referred to as

As DNA unwinds and denatures, absorbance is predicted to

The figure below shows part of the primary structure of DNA. Identify the nucleotide.

The basic structure of DNA is a right-handed helix formed by two strands of DNA.

Predict the complementary strand of the following DNA sequence: 5 ^' -ATCTGAATCT-3 ^'

The figure below shows part of the primary structure of DNA. Identify the nucleoside.

Chargaff's rule is that the amount of

How many base pairs per turn does B-DNA contain?

The DNA double helix is considered to be a structure.

The DNA of a bacteria was isolated and it was determined that 15% of the DNA is composed of cytosine. What percentage of the DNA is adenine?

What is the melting temperature from the DNA absorbance shown in the figure below? $What is the melting temperature from the DNA absorbance shown in the figure below? A) 80 \degree C B) 85 \degree C C) 90 \degree C D) 95 \degree C$

The interior stacking of the DNA bases in the double helix provides stability through