Question 1

In DNA replication in E. coli, the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNA polymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following results would you expect?
A) Replication would only occur on the leading strand.
B) Replication would only occur on the lagging strand.
C) Replication would not occur on either the leading or lagging strand.
D) Replication would not be affected as the enzyme primase in involved with RNA synthesis.

Accepted Answer

If a mutation occurs in the primase gene, primase would not be able to attach the 5 to 10 base ribonucleotide strand to serve as a starting point for DNA polymerase. Without the RNA primer, DNA replication cannot occur. Therefore, replication would not occur on either the leading or lagging strand.

Question 2

In a healthy eukaryotic cell, the rate of DNA repair is typically equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?
A) The cell can be transformed into a cancerous cell.
B) RNA may be used instead of DNA as inheritance material.
C) DNA replication will proceed more quickly.
D) DNA replication will continue by a new mechanism.

Accepted Answer

If the rate of DNA repair lags behind the rate of mutation, the cell is more likely to accumulate mutations that could lead to uncontrolled cell growth and transformation into a cancerous cell. This is because certain mutations can activate oncogenes or inactivate tumor suppressor genes, leading to uncontrolled cell division and tumor formation.

Question 3

In analysing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?
A) A = G
B) A + G = C + T
C) A + T = G + C
D) A = C

Accepted Answer

According to the base-pairing rules in DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Therefore, the total number of purines (A + G) should equal the total number of pyrimidines (C + T).

Question 4

Hershey and Chase (1952) used a DNA-based virus for their work. How might the results have been different if they had used an RNA virus?
A) With an RNA virus, radioactive protein would have been in the final pellet.
B) With an RNA virus, radioactive RNA would have been in the final pellet.
C) With an RNA virus, neither sample would have had a radioactive pellet.
D) With an RNA virus, the protein shell would have been radioactive in both samples.

Accepted Answer

The Hershey and Chase experiment used bacteriophages to determine whether DNA or protein was the genetic material. Since the bacteriophages had DNA as their genetic material, radioactive DNA was found in the final pellet. If an RNA-based virus had been used, radioactive RNA would have been found in the final pellet instead of radioactive DNA. Therefore, the correct choice is B.

Question 5

Which of the following types of cells are affected most by telomere shortening?
A) only prokaryotic cells
B) only eukaryotic cells
C) cells in prokaryotes and eukaryotes
D) only animal cells

Accepted Answer

Telomeres are present at the ends of eukaryotic chromosomes, and as cells divide, the telomeres shorten. Therefore, eukaryotic cells are the ones most affected by telomere shortening, whereas prokaryotic cells lack telomeres. Although animal cells are also eukaryotic, telomere shortening affects all eukaryotic cells, not just animal cells.

Question 6

Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results?
A) The single-strand binding proteins were malfunctioning during DNA replication.
B) There were one or more base pair mismatches in the RNA primer.
C) The proofreading mechanism of DNA polymerase was not working properly.
D) The DNA polymerase was unable to add bases to the 3′ end of the growing nucleic acid chain.

Accepted Answer

The proofreading mechanism of DNA polymerase is responsible for detecting and correcting errors in DNA replication. If this mechanism is not functioning properly, it could lead to a higher mutation rate. The other answer choices do not directly relate to the proofreading mechanism and are less likely to cause such a large increase in mutation rates.

Question 7

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular ageing?
A) Telomerase will speed up the rate of cell proliferation.
B) Telomerase eliminates telomere shortening and retards ageing.
C) Telomerase shortens telomeres, which delays cellular ageing.
D) Telomerase would have no effect on cellular ageing.

Accepted Answer

Telomerase eliminates telomere shortening and retards ageing. The shortening of telomeres with each cell division is associated with cellular ageing, and telomerase can extend the life of cells beyond their normal lifespan by adding new telomeric DNA to the ends of chromosomes. Therefore, adding telomerase to cells would eliminate telomere shortening and delay cellular ageing.

Question 8

In his work with pneumonia-causing bacteria and mice, Griffith found that
A) the protein coat from pathogenic cells was able to transform nonpathogenic cells.
B) heat-killed pathogenic cells caused pneumonia.
C) some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic.
D) the polysaccharide coat of bacteria caused pneumonia.

Accepted Answer

Griffith's experiments showed that some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. This was the first demonstration of bacterial transformation and the discovery of DNA as the genetic material. Choices A and D are incorrect because Griffith did not work with protein or polysaccharide coats in his transformation experiments. Choice B is incorrect because heat-killed pathogenic cells alone did not cause pneumonia in Griffith's experiments – it was the substance they released that caused the transformation.

Question 9

Which of the following statements accurately describes the structure of a eukaryotic chromosome?
A) It is composed of a single strand of DNA.
B) It is constructed as a series of nucleosomes wrapped around two DNA molecules.
C) It has different numbers of genes in different cell types of an organism.
D) It is a single linear molecule of double-stranded DNA plus proteins.

Accepted Answer

Eukaryotic chromosomes are composed of a single linear molecule of double-stranded DNA plus proteins, including histones that help package the DNA into a compact structure. This DNA-protein complex is organized into repeating units called nucleosomes, but the chromosome as a whole is not constructed as a series of nucleosomes wrapped around two DNA molecules. The number of genes in a eukaryotic chromosome is generally the same across all cell types of an organism.

Question 10

Which of the following effects might be caused by reduced or very little active telomerase activity?
A) Cells may become cancerous.
B) Telomere lengthens in germ cells.
C) Cells age and begin to lose function.
D) Cells maintain normal functioning.

Accepted Answer

Telomerase activity helps maintain telomere length, which is important for cell division and function. Reduced or very little active telomerase activity can result in shortened telomeres, leading to cellular senescence (aging) and loss of function. This can also contribute to age-related diseases such as cardiovascular disease and neurodegenerative disorders. Option A is incorrect because reduced telomerase activity can actually reduce the risk of cancer because it limits the number of times a cell can divide. Option B is incorrect because germ cells naturally have high telomerase activity and do not typically experience telomere shortening. Option D is incorrect because reduced telomerase activity is known to have negative effects on cell function.

Question 11

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesised?
A) The origins of replication occur only at the 5′ end.
B) Helicases and single-strand binding proteins work at the 5′ end.
C) DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel.
D) DNA ligase works only in the 3′ → 5′ direction.

Accepted Answer

The difference in how the leading and lagging strands of DNA molecules are synthesized is based on the fact that DNA polymerase can add new nucleotides only to the 3′ end of a pre-existing strand. Therefore, the leading strand, which runs in the 5′ to 3′ direction, can be continuously synthesized in the 5′ to 3′ direction, while the lagging strand, which runs in the opposite 3′ to 5′ direction, must be synthesized in short fragments called Okazaki fragments. These fragments are later joined together by DNA ligase to complete the lagging strand synthesis.

Question 12

Which of the following lists represents the order of increasingly higher levels of organisation of chromatin?
A) nucleosome, 30-nm chromatin fibre, looped domain
B) looped domain, 30-nm chromatin fibre, nucleosome
C) nucleosome, looped domain, 30-nm chromatin fibre
D) 30-nm chromatin fibre, nucleosome, looped domain

Accepted Answer

The correct order of increasingly higher levels of chromatin organization is nucleosome, 30-nm chromatin fibre, looped domain.

Question 13

The lagging strand is characterised by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki fragments gave evidence for which of the following ideas?
A) DNA polymerase is an enzyme that synthesises leading and lagging strands during replication only in one direction.
B) DNA is a polymer consisting of four monomers: adenine, thymine, guanine and cytosine.
C) DNA is the genetic material.
D) Bacterial replication is fundamentally different from eukaryotic replication. The key should not be way longer than the distractors.

Accepted Answer

The existence of Okazaki fragments indicated that DNA polymerase must synthesise the lagging strand in a discontinuous manner, creating short segments that must be joined together. This is because DNA polymerase can only synthesise in one direction on each strand, meaning that on the lagging strand, it must repeatedly jump back and start a new segment, rather than synthesising continuously like it does on the leading strand. This information supports the idea presented in option A. Option B is simply a statement of basic DNA structure, not specific to this experiment. Option C is true but not directly related to this experiment. Option D is false.

Question 14

What are 'telomeres'?
A) The structures that hold two sister chromatids together.
B) Enzymes that elongate the DNA strand during replication.
C) The sites of origin of DNA replication.
D) The ends of linear chromosomes.

Accepted Answer

Telomeres are the repetitive DNA sequences located at the ends of linear chromosomes in eukaryotic cells. They protect the genetic information from degradation and ensure the proper replication and stability of chromosomes.

Question 15

Which of the following molecular characteristics cause histones to bind tightly to DNA?
A) Histones are positively charged, and DNA is negatively charged.
B) Histones are negatively charged, and DNA is positively charged.
C) Both histones and DNA are strongly hydrophobic.
D) Histones are covalently linked to the DNA.

Accepted Answer

Histones are positively charged due to the presence of many lysine and arginine residues, while DNA is negatively charged due to the presence of phosphate groups on the sugar-phosphate backbone. This electrostatic attraction between the positive histones and negative DNA causes histones to bind tightly to DNA.

Question 16

Which of the following statements correctly describes the difference between the leading strand and the lagging strand in DNA replication?
A) The leading strand is synthesised in the 3' → 5' direction in a discontinuous fashion, while the lagging strand is synthesised in the 5' → 3' direction in a continuous fashion.
B) The leading strand is synthesised continuously in the 5' → 3' direction, while the lagging strand is synthesised discontinuously in the 5' → 3' direction.
C) The leading strand requires an RNA primer, whereas the lagging strand does not.
D) There are different DNA polymerases involved in elongation of the leading strand and the lagging strand.

Accepted Answer

The leading strand is synthesised continuously in the 5' → 3' direction, while the lagging strand is synthesised discontinuously in the 5' → 3' direction. The lagging strand is synthesised in fragments called Okazaki fragments, which are then ligated together. The leading strand does not require an RNA primer and is elongated by DNA polymerase III, whereas the lagging strand requires an RNA primer and is elongated by both DNA polymerase III and DNA polymerase I.

Question 17

Which of the following statements correctly describes the structure of chromatin?
A) Heterochromatin is composed of DNA, whereas euchromatin is made of DNA and RNA.
B) Both heterochromatin and euchromatin are found in the cytoplasm.
C) Heterochromatin is highly condensed, whereas euchromatin is less compact.
D) Euchromatin is not transcribed, whereas heterochromatin is transcribed.

Accepted Answer

Heterochromatin is highly condensed, whereas euchromatin is less compact.

Question 18

If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?
A) There would be an increase in the amount of DNA produced during replication.
B) The cell's DNA could not be packed into its nucleus.
C) Spindle fibres would not form during prophase.
D) Amplification of other genes would compensate for the lack of histones.

Accepted Answer

Histone proteins are responsible for packaging and organizing DNA into compact structures known as nucleosomes. Without histone proteins, DNA would be unable to properly pack into the nucleus and form chromosomes. This would lead to significant problems during cell division and overall cell function.

Question 19

Which of the following structural characteristics is most critical for the association between histones and DNA?
A) Histones are small proteins.
B) Histones are highly conserved (that is, histones are very similar in every eukaryote).
C) There are at least five different histone proteins in every eukaryote.
D) Histones are positively charged.

Accepted Answer

Histones are positively charged, which allows them to bind to the negatively charged phosphate groups in DNA. This interaction is critical for the formation and stability of chromatin structure.

Question 20

Which of the following statements accurately describes one characteristic of histones?
A) Each nucleosome consists of two molecules of histone H1.
B) Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.
C) The carboxyl end of each histone extends outward from the nucleosome and is called a 'histone tail'.
D) Histones are found in mammals, but not in other animals or in plants or fungi.

Accepted Answer

The answer of Which of the following statements accurately describes...

Quiz 16: The Molecular Basis of Inheritance

In a healthy eukaryotic cell, the rate of DNA repair is typically equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?

In analysing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?

Hershey and Chase (1952) used a DNA-based virus for their work. How might the results have been different if they had used an RNA virus?

Which of the following types of cells are affected most by telomere shortening?

Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results?

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular ageing?

In his work with pneumonia-causing bacteria and mice, Griffith found that

Which of the following statements accurately describes the structure of a eukaryotic chromosome?

Which of the following effects might be caused by reduced or very little active telomerase activity?

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesised?

Which of the following lists represents the order of increasingly higher levels of organisation of chromatin?

The lagging strand is characterised by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki fragments gave evidence for which of the following ideas?

What are 'telomeres'?

Which of the following molecular characteristics cause histones to bind tightly to DNA?

Which of the following statements correctly describes the difference between the leading strand and the lagging strand in DNA replication?

Which of the following statements correctly describes the structure of chromatin?

If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?

Which of the following structural characteristics is most critical for the association between histones and DNA?

Which of the following statements accurately describes one characteristic of histones?