Question 1

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

Accepted Answer

A nucleotide is composed of three parts: a nitrogenous base (adenine, guanine, cytosine or thymine), a deoxyribose sugar, and a phosphate group. Therefore, option (D) is the correct choice as it includes all three parts that make up a nucleotide.

Question 2

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) there are so few of them.
C) the hydrogen bonds in DNA are different than the hydrogen bonds in other molecules.
D) the hydrogen bonds in DNA also have a very special type of molecular glue.
E) ten of them form between each DNA base pair.

Accepted Answer

Hydrogen bonds are weaker than ionic or covalent bonds, but the DNA double helix is stabilized by the large number of hydrogen bonds between complementary base pairs, making the overall structure stable.

Question 3

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.
E) DNA and RNA are not the same molecule.

Accepted Answer

Antiparallelism refers to the fact that the two strands of DNA run in opposite directions, with one strand going in the 5' to 3' direction and the other going in the 3' to 5' direction. This arrangement is important for the process of DNA replication and other cellular functions.

Question 4

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.
E) 3.2 billion.

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 5

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

Accepted Answer

A (adenine) is always complementary to T (thymine) in DNA because they form two hydrogen bonds, while C (cytosine) always pairs with G (guanine) forming three hydrogen bonds. C and T are not complementary and neither are C and C, nor G and G.

Question 6

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

Accepted Answer

Cytosine binds with guanine through three hydrogen bonds, forming the G-C base pair in DNA. Uracil is found in RNA instead of thymine, which pairs with adenine. Amino acids are the building blocks of proteins and are not directly involved in DNA base pairing.

Question 7

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

Accepted Answer

DNA entwined around a group of eight proteins (called histones) is called a nucleosome. This structure helps to package DNA tightly into the nucleus of a cell.

Question 8

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) there are eight types of bases.
D) the bases form a sequence, and the sugar-phosphate backbone does not.
E) the sugar-phosphate backbone is highly unstable.

Accepted Answer

The base pairs, specifically the sequence of the bases (adenine, guanine, cytosine, and thymine), provide the genetic information that is transcribed and translated into proteins. The sugar-phosphate backbone, on the other hand, serves a structural role by supporting and protecting the base pairs, but does not contribute to the genetic information. Therefore, the best choice is D.

Question 9

A scientist discovers a virus whose genome consists of an unusual DNA strand from a virus.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.
E)The experiment was contaminated with cockroach DNA.

Accepted Answer

The unequal percentages of adenine and thymine, as well as guanine and cytosine, suggest that the DNA is single-stranded, as Chargaff's rules apply to double-stranded DNA where A pairs with T and G pairs with C.

Question 10

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.
E) 90% DNA and 20% proteins.

Accepted Answer

Chromatin consists of around 30% histones, 30% DNA binding proteins, and 30% DNA. The remaining 10% is RNA. Therefore, option C is the closest to the actual percentages. Option E is not correct as it adds up to a total of 110%, while option A and B have incorrect percentages. Option D has a total of 90%, which is insufficient to explain the constituents of chromatin.

Question 11

Meselson and Stahl's experiment followed
A) the distribution of different-weighted DNA over three generations of bacteria.
B) the distribution of different-labeled DNA over three generations of humans.
C) the ability of a protease or nuclease to stop the transmission of DNA over generations.
D) viruses injecting their DNA into bacteria.
E) 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 different isotopic mediums to track the distribution of different-weighted DNA over three generations. This helped confirm the theory of semiconservative replication in DNA.

Question 12

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'
E) 3' AUGGCAU 5'

Accepted Answer

To find the complementary strand of DNA, we need to pair the nitrogenous bases in accordance with the base-pairing rules: A with T and C with G. 
So the complementary strand to 5' ATGGCAT 3' would be 3' TACCGTA 5'.

Question 13

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.
E) mirror.

Accepted Answer

The numbered carbons in the sugars (specifically, carbon #5 and carbon #3) are directional and determine the polarity of the DNA strand. This polarity affects the way the strands of DNA align and pair together in the double helix.

Question 14

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.
E) discontinuous and not continuous.

Accepted Answer

Meselson and Stahl's experiments provided evidence that DNA replication is a semi-conservative process, in which each newly synthesized DNA molecule has one parent strand and one newly synthesized strand. They ruled out the dispersive model and the conservative model, which proposed different mechanisms of DNA replication. They also showed that DNA replication is continuous, not discontinuous.

Question 15

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) A gene is composed of amino acids whose sequence encodes a particular protein.
E) DNA is composed of amino acids, which encode the protein and genotype.

Accepted Answer

A gene is a section of DNA that contains the instructions needed to make a functional protein. The sequence of nucleotides in the gene determines the sequence of amino acids in the protein. Proteins are not composed of DNA or amino acids themselves, but rather they are made up of chains of amino acids. Therefore, option A is the most accurate statement regarding genes, DNA, and proteins.

B) A gene is composed of DNA, not amino acids. 
C) DNA is the blueprint for genes, but genes themselves are not composed of amino acid sequences. 
D) This statement is not accurate as genes are composed of nucleotides, not amino acids. 
E) This statement is also not accurate as DNA and amino acids are two different types of molecules.

Question 16

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

Accepted Answer

DNA in the nucleus is associated with histones, which help organize DNA into compact and efficient structures.

Question 17

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

Accepted Answer

Adenine is a purine, and thymine is a pyrimidine.

Question 18

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.
E) about 40,000 DNA bases long.

Accepted Answer

One kilobase (kb) is equal to 1,000 nucleotides, so a gene that is 13,066 nucleotides long is about 13.1 kb long. Therefore, the best choice is B, which indicates that the gene is about 1.3 kilobases long.

Question 19

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

Accepted Answer

Purine bases (adenine and guanine) form hydrogen bonds with pyrimidine bases (thymine and cytosine) in DNA. Hydrogen bonds are weak interactions between a partially positively charged hydrogen atom and a partially negatively charged atom (often oxygen or nitrogen) in a nearby molecule.

Question 20

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, thymine and uracil) are nitrogenous bases that pair up to form the ladder-like structure of DNA molecules.

Quiz 9: DNA Structure and Replication

A nucleotide consists of

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

Antiparallelism means that

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

Which base pair is complementary?

In DNA,cytosine binds with

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

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

A scientist discovers a virus whose genome consists of an unusual DNA strand from a virus.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

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

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

Meselson and Stahl's experiments showed that DNA replication is

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

DNA in the nucleus winds around proteins called

The nitrogenous bases adenine and thymine are

A gene is 13,066 nucleotides long.This is

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

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