Question 1

The bonds that hold DNA and RNA together are known as __________.

Accepted Answer

The bonds that hold DNA and RNA together are known as 3'-5'-phosphodiester linkages, which connect adjacent nucleotides in a polynucleotide chain through a phosphate group bridging the 3' hydroxyl group on one sugar to the 5' hydroxyl group on the next sugar. The other choices are incorrect because peptide bonds connect amino acids in proteins, 1,4-glycosidic linkages connect monosaccharides in carbohydrates, and phosphate esters are a broader category of compounds that include the phosphate group in DNA and RNA but also other molecules.

Question 2

The genome is essentially equivalent to all of the genetic information that is present in a ______ set of chromosomes.

Accepted Answer

The genome is the complete set of genetic information in a haploid set of chromosomes, which includes all the genes and non-coding sequences.

Question 3

What technique supplied the data that led Watson and Crick to the double helical structure of DNA?

Accepted Answer

X-ray diffraction/crystallography was the technique used by Rosalind Franklin to create images of DNA fibers that showed evidence of a helical structure. These images, combined with data from other experiments, provided the clues that led to Watson and Crick’s discovery of the double helical structure of DNA.

Question 4

The information encoded in DNA resides in ________.

Accepted Answer

The information encoded in DNA is stored in the sequence of its four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order and combination of these bases in a DNA molecule determines the genetic instructions for the development, function, and maintenance of all living organisms. The phosphate groups and sugars make up the backbone of the DNA molecule and do not contain genetic information. The phosphodiester linkages connect nucleotides within each strand of DNA, but do not determine the sequence of bases.

Question 5

The ends of a polynucleotide chain are the ____ end and the ____ end.

Accepted Answer

The ends of a polynucleotide chain are labeled according to their polarity. The 5' end contains a phosphate group attached to the 5' carbon of the sugar, while the 3' end has a hydroxyl group on the 3' carbon of the sugar. Therefore, the correct answer is 3',5'. N-terminal and C-terminal are used to describe the ends of amino acid chains in proteins, not polynucleotide chains.

Question 6

Which type of DNA sequence is typified by short sequences of DNA (five to a few hundred base pairs in length)repeated a large number of times in tandem to form very large clusters,each containing up to several million base pairs of DNA?

Accepted Answer

This describes satellite DNAs, which are characterized by short (five to a few hundred base pairs) sequences repeated in tandem to form large clusters (up to several million base pairs). Minisatellite DNAs and microsatellite DNAs also have repeated sequences, but they are not typically found in such large clusters. Consensus sequences are not necessarily repeated in tandem, and microminisatellite DNAs are not a recognized category of DNA sequences.

Question 7

The original model of DNA structure stated that each unit of structure in DNA contained all four nitrogenous bases; it was called the ________.

Accepted Answer

The original model of DNA structure was called the Tetranucleotide Theory, which stated that each unit of structure in DNA contained all four nitrogenous bases - adenine, thymine, cytosine, and guanine - repeating in a fixed sequence. This theory was later proven incorrect with the discovery of the double helix structure of DNA.

Question 8

Which type of enzyme makes a transient break in both DNA duplex strands and then transports another segment of a DNA molecule (or separate molecule entirely)through the break and reseals the severed strands?

Accepted Answer

Type II topoisomerases are the enzymes that make a transient break in both DNA duplex strands and transport another segment of a DNA molecule (or separate molecule entirely) through the break and reseal the severed strands. Type I topoisomerases make a transient break in only one strand of the DNA duplex. There is no such thing as a Type I topologicase or Type II topologicase. Type I isomerases are responsible for changing the topological state of DNA without breaking strands.

Question 9

What statement below explains the uniform width of the DNA molecule along its entire width?

Accepted Answer

A pyrimidine nitrogenous base always pairs with a purine nitrogenous base, maintaining a consistent width of the DNA double helix.

Question 10

Which of the following is guanosine?

Accepted Answer

Guanosine is a nucleoside consisting of the nitrogenous base guanine attached to a ribose sugar.

Question 11

How is the extent of DNA denaturation usually measured?

Accepted Answer

The absorbance of UV light by DNA increases as DNA denatures, so measuring the absorbance of UV light is a common method for determining the extent of DNA denaturation.

Question 12

You isolate DNA from a particular organism and analyze it.The amount of adenine was 6 µmoles and the A+T/G+C ratio is 4.0.How much guanine should be in the sample?

Accepted Answer

The total moles of nucleotides in the sample can be calculated by the A+T/G+C ratio formula:
A + T = (4/5) * (G + C)
We know that A = 6 µmoles. Therefore:
T = (4/5) * (G + C) - 6 µmoles
The total moles of nucleotides:
A + T + G + C = (4/5) * (G + C) + G + C
A + T + G + C = (9/5) * (G + C)
A + T + G + C = (9/5) * (G + C) = 6 + T + G + C
Therefore, G + C = (5/4) * (A + T) = 7.5 µmoles
Since A = 6 µmoles, T = (4/5) * (G + C) - 6 µmoles = (4/5) * 7.5 µmoles - 6 µmoles = 0.5 µmoles
The total amount of G and C is 7.5 µmoles, and the ratio of G to C is 1:1, therefore:
G = C = (7.5 µmoles) / 2 = 3.75 µmoles
The amount of guanine in the sample is half the amount of G and C, therefore:
Guanine = 3.75 / 2 = 1.875 ≈ 1.5 µmoles
Therefore, the best choice is C.

Question 13

The variety and number of DNA sequence copies in the genome are known as genome _______.

Accepted Answer

The variety and number of DNA sequence copies in the genome refer to its complexity, which is correctly represented by choice C. Choices A, B, D, and E do not accurately reflect this concept.

Question 14

What gives a DNA molecule its negative charge?

Accepted Answer

The phosphate groups in the DNA molecule contain negatively charged ions, which give the DNA molecule its overall negative charge.

Question 15

________ refers to the fact that the sequence of one DNA strand specifies the sequence of the other strand in the double helix.

Accepted Answer

Complementarity refers to the fact that one strand of DNA is complementary to the other strand, meaning that the sequence of one strand determines the sequence of the other strand. This is a fundamental aspect of DNA structure and the basis for DNA replication and transcription.

Question 16

Which type of enzyme is essential for processes like DNA replication and transcription to prevent excessive supercoiling from developing as the complementary strands of the DNA duplex separate and unwind?

Accepted Answer

Topoisomerase enzymes are responsible for preventing excessive supercoiling during DNA replication and transcription. They achieve this by cutting one or both strands of the DNA, allowing them to rotate and relieve the supercoiling tension before rejoining the strands. Telomerase is involved in adding telomere repeats to the ends of chromosomes, not in preventing supercoiling. Topologicase and isomerase are not real enzymes. Helicase is involved in separating the complementary strands of DNA during replication and transcription, but it is not specifically responsible for preventing supercoiling.

Question 17

Different versions of a gene are called _________.

Accepted Answer

Different versions of a gene are called alleles.

Question 18

What function does topoisomerase II serve during mitosis?

Accepted Answer

Topoisomerase II is required for disentangling DNA molecules before sister chromatids can be separated during mitosis. It helps to relieve the tension that builds up as the double helix is unwound and replicated, allowing the chromosome to become less compact and more flexible. Without topoisomerase II, the DNA would become hopelessly intertwined and mitosis would fail.

Question 19

Why are satellite DNAs separated from the bulk of the genome during density gradient centrifugation?

Accepted Answer

Satellite DNAs have significantly different base compositions than the bulk of the genome, which allows them to form separate bands during density gradient centrifugation.

Question 20

In a right-handed double helix,if one looks down the central axis of the molecule,_________.

Accepted Answer

In a right-handed double helix, each strand follows a clockwise path as it moves away from the observer when one looks down the central axis of the molecule.

Quiz 10: The Nature of the Gene and the Genome