Question 1

Which base pair is complementary?
A)A and T
B)C and T
C)A and G
D)C and C

Accepted Answer

According to the base pairing rule in DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). Therefore, A and T are complementary base pairs.

Question 2

Purines and pyrimidines refer to the _____ of the DNA molecules.
A)nitrogenous bases
B)sugar-phosphate backbone
C)hydrogen bonds
D)nucleus
E)histones

Accepted Answer

Purines (adenine and guanine) and pyrimidines (cytosine and thymine) are nitrogenous bases that make up the building blocks of DNA molecules. The sugar-phosphate backbone, hydrogen bonds, nucleus, and histones are other components of DNA, but they are not what purines and pyrimidines specifically refer to.

Question 3

Meselson and Stahl's experiments showed that DNA replication is
A)dispersive,conservative,and semi-conservative.
B)dispersive,but not conservative or semi-conservative.
C)semi-conservative,but not dispersive or conservative.
D)quasi-conservative,but not dispersive or semi-conservative.

Accepted Answer

Meselson and Stahl's experiments provided evidence that DNA replication is semi-conservative, meaning that each strand of the original DNA molecule serves as a template for the synthesis of a new complementary strand, resulting in two daughter DNA molecules, each with one original and one newly synthesized strand. Their experiments ruled out the possibilities of conservative and dispersive models of DNA replication.

Question 4

A scientist discovers a virus whose genome consists of an unusual DNA strand.She finds the following percentage of bases: 23% A,12% T,30% G,and 35%C.Which of the following best explains these results?
A)The bases are not purines or pyrimidines.
B)Chargaff was wrong.
C)Linus Pauling's model of DNA was correct.
D)The DNA in this virus is single-stranded.

Accepted Answer

In double-stranded DNA, Chargaff's rules state that the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). The unequal percentages of bases suggest that the DNA is single-stranded, where these rules do not apply.

Question 5

Chromatin consists of about
A)10% histones,30% DNA binding proteins,30% DNA,and 30% RNA.
B)25% histones,25% DNA binding proteins,25% DNA,and 25% RNA.
C)30% histones,30% DNA binding proteins,30% DNA,and 10% RNA.
D)10% histones,10% DNA binding proteins,70% DNA,and 10% RNA.

Accepted Answer

Chromatin consists of approximately 30% histones, 30% DNA binding proteins, 30% DNA, and 10% RNA. This composition allows for the compact packaging of DNA within the nucleus, while also providing the necessary structural support and regulation of gene expression.

Question 6

Meselson and Stahl's experiment followed
A)the distribution of different-weighted DNA over multiple generations of bacteriA.
B)the ability of a protease or nuclease to stop the transmission of DNA over generations.
C)viruses injecting their DNA into bacteria.
D)DNA sequences in people who are politically liberal compared to those who are sometimes politically conservative.

Accepted Answer

Meselson and Stahl's experiment involved growing bacteria in a medium containing heavy nitrogen (15N) and then transferring them to a medium containing light nitrogen (14N). They observed the distribution of different-weighted DNA over multiple generations of bacteria and showed that DNA replication is semiconservative. The experiment did not involve proteases, nucleases, or political ideologies.

Question 7

In DNA,cytosine binds with
A)uracil.
B)adenine.
C)thymine.
D)guanine.

Accepted Answer

Cytosine binds with guanine in DNA through three hydrogen bonds.

Question 8

A gene is 13,066 nucleotides long.This is
A)about 1.3 microbases.
B)about 1.3 kilobases.
C)about 1.3 megabases.
D)about 3,011 amino acids.

Accepted Answer

One kilobase is equivalent to 1000 nucleotides, therefore 13,066 nucleotides is 13.066 kilobases.

Question 9

A nucleotide consists of
A)three sugars for every phosphate.
B)three phosphates for every sugar.
C)one deoxyribose sugar,one nitrogenous base,and one phosphate group.
D)three DNA bases.

Accepted Answer

A nucleotide is composed of three basic components: a nitrogenous base (adenine, guanine, cytosine, or thymine in DNA), a five-carbon sugar (deoxyribose in DNA), and a phosphate group. So, the correct answer is that a nucleotide consists of one deoxyribose sugar, one nitrogenous base, and one phosphate group.

Question 10

DNA in the nucleus winds around proteins called
A)histones.
B)karyosomes.
C)ribosomes.
D)proteasomes.

Accepted Answer

DNA in the nucleus winds around proteins called histones.

Question 11

When DNA folds and winds into the nucleus of a cell,it shrinks in length by a factor of
A)10.
B)100.
C)1,000.
D)7,000.

Accepted Answer

DNA shrinks in length by a factor of approximately 7,000 when it folds and winds into the nucleus, allowing it to fit within the small space of the cell nucleus.

Question 12

The directional nature of the DNA double helix is observed in the
A)locations of the hydrogen bonds.
B)locations of the numbered carbons in the sugars.
C)locations of the oxygen atom in the phosphate.
D)double helix when it is separated into single strands.

Accepted Answer

The DNA double helix has a directional nature due to the orientation of the sugars. The sugars have a 5' end and a 3' end, with the 5' end having a phosphate group and the 3' end having a hydroxyl group. The numbering of the carbons in the sugar molecule is based on this orientation, with the 5' carbon being numbered first and the 3' carbon being numbered last. This directionality is important for DNA replication, transcription, and translation.

Question 13

Which of the following is most correct regarding genes,DNA,and protein?
A)A gene is a section of DNA whose sequence encodes a particular protein,which is composed of amino acids.
B)A gene is a section of a chromosomal DNA composed of many amino acids.
C)DNA is composed of many genes,which are formed from amino acid sequences.
D)DNA is composed of amino acids,which encode the protein and genotype.

Accepted Answer

A gene is a specific sequence of DNA that encodes a particular protein by specifying the order in which amino acids are linked together to form the protein. Therefore, option A is the most correct regarding genes, DNA, and protein. Option B and C are incorrect because genes are not composed of amino acids and DNA does not form genes; rather, DNA contains the information to make genes. Option D is incorrect because DNA is not composed of amino acids.

Question 14

Hydrogen bonds are not as strong as ionic or covalent bonds,but they are able to hold the DNA double helix together because
A)there are so many of them.
B)the hydrogen bonds in DNA differ from hydrogen bonds in other molecules.
C)the hydrogen bonds in DNA also have a very special type of molecular glue.
D)ten of them form between each DNA base pair.

Accepted Answer

Hydrogen bonds are individually weak, but the large number of them in the DNA double helix provides significant cumulative strength to hold the two strands together.

Question 15

If the sequence of one strand of a DNA molecule is 5' ATGGCAT 3',the sequence of the complementary strand is:
A)5' ATGGCAT 3'
B)3' ATGGCAT 5'
C)5' TACCGTA 3'
D)3' TACCGTA 5'

Accepted Answer

The complementary strand will have the same sequence as the original strand, but with base pairs that complement the ones in the original strand. In DNA, Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G). So, for the original sequence 5' ATGGCAT 3', the complementary sequence must have T instead of A and G instead of C. This gives us the sequence 3' TACCGTA 5', which corresponds to choice D.

Question 16

DNA entwined around an octet of proteins is called a(n)
A)nucleotide.
B)karyosome.
C)nucleosome.
D)ribosome.

Accepted Answer

DNA entwined around an octet of proteins is called a nucleosome. This structure is made up of four pairs of histone proteins and helps to compact DNA within the cell's nucleus.

Question 17

In a molecule of DNA,purine bases form _____ bonds with pyrimidine bases.
A)phosphate
B)hydrogen
C)disulfide
D)covalent

Accepted Answer

Purine and pyrimidine bases form hydrogen bonds with each other. Specifically, adenine (purine) forms two hydrogen bonds with thymine (pyrimidine) and guanine (purine) forms three hydrogen bonds with cytosine (pyrimidine).

Question 18

In a DNA molecule,the base pairs provide information,and the sugar-phosphate backbone does not,because
A)the base pairs are all the same,but the sugar-phosphate backbone varies.
B)there are eight types of base pairs.
C)the bases form a sequence,and the sugar-phosphate backbone does not.
D)the sugar-phosphate backbone is highly unstable.

Accepted Answer

The sequence of the bases in the DNA molecule provides the genetic information. The sugar-phosphate backbone, on the other hand, functions only to provide structural support and stability to the DNA molecule. It does not carry any genetic information, as the order of the sugar and phosphate molecules in the backbone is constant and does not vary.

Question 19

The nitrogenous bases adenine and thymine are
A)both purines.
B)both pyrimidines.
C)a purine and a pyrimidine,respectively.
D)a pyrimidine and a purine,respectively.

Accepted Answer

Adenine is a purine, and thymine is a pyrimidine.

Question 20

Antiparallelism means that
A)the two strands of a DNA molecule run in opposite directions.
B)the DNA double helix twists first one way,then the other.
C)the DNA bases are sometimes on the outside of the molecule.
D)the DNA molecule cannot dissolve in water.

Accepted Answer

Antiparallelism refers to the opposite directionality of the two strands in a DNA molecule. One strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction. This allows for precise base pairing and plays a key role in DNA replication and transcription.

Quiz 9: DNA Structure and Replication

Which base pair is complementary?

Purines and pyrimidines refer to the _____ of the DNA molecules.

Meselson and Stahl's experiments showed that DNA replication is

A scientist discovers a virus whose genome consists of an unusual DNA strand.She finds the following percentage of bases: 23% A,12% T,30% G,and 35%C.Which of the following best explains these results?

Chromatin consists of about

Meselson and Stahl's experiment followed

In DNA,cytosine binds with

A gene is 13,066 nucleotides long.This is

A nucleotide consists of

DNA in the nucleus winds around proteins called

When DNA folds and winds into the nucleus of a cell,it shrinks in length by a factor of

The directional nature of the DNA double helix is observed in the

Which of the following is most correct regarding genes,DNA,and protein?

Hydrogen bonds are not as strong as ionic or covalent bonds,but they are able to hold the DNA double helix together because

If the sequence of one strand of a DNA molecule is 5' ATGGCAT 3',the sequence of the complementary strand is:

DNA entwined around an octet of proteins is called a(n)

In a molecule of DNA,purine bases form _____ bonds with pyrimidine bases.

In a DNA molecule,the base pairs provide information,and the sugar-phosphate backbone does not,because

The nitrogenous bases adenine and thymine are

Antiparallelism means that