Question 1

Which are advantages of using recombinant DNA technology when compared with the gamma garden method of detecting favorably mutated crop varieties? (Select all correct choices)

Accepted Answer

Recombinant DNA technology avoids the risks associated with radioactive isotopes and allows for targeted genetic modifications, unlike the random mutations in gamma gardens.

Question 2

Autonomous replicating sequences that have been isolated and analyzed share several distinct elements. Which distinct elements below are shared by autonomous replicating sequences? (Select all correct choices)

Accepted Answer

Autonomous replicating sequences share the core element and a conserved sequence of 11 base pairs, which functions as a specific binding site for the origin recognition complex. The conserved sequence of 11 base pairs does not function as the origin recognition complex itself, so option C is incorrect. Option D refers to a sequence of 22 base pairs, which is not mentioned in the question, so it is also incorrect.

Question 3

Patients with the classical form of xeroderma pigmentosum have a defect in one of the genes involved in ______________.

Accepted Answer

Xeroderma pigmentosum is associated with a defect in nucleotide excision repair, which is responsible for repairing DNA damage caused by UV radiation. This defect leads to an increased risk of skin cancers and other types of tumors.

Question 4

A double-stranded breakage repair pathway that requires the presence of a second chromosome carrying the same sequence of genes as the damaged chromosome is called _________.

Accepted Answer

Homologous recombination involves the use of a second, homologous chromosome to repair double-stranded breaks. Nonhomologous end joining repair (NHEJ) does not require a homologous chromosome and instead directly joins the broken ends together. DNA methylation repair and nonhomologous recombination are not established repair pathways.

Question 5

Using DNA to store data has the advantage of __________________. (Select all correct choices)

Accepted Answer

DNA is a stable molecule, can store large amounts of data in a small volume, and has a higher data density than binary systems.

Question 6

Using DNA to store data has the disadvantage of __________________. (Select all correct choices)

Accepted Answer

DNA data storage is slow to read and write compared to electronic systems, and mutations can occur during replication, potentially leading to data corruption.

Question 7

What must the mismatch repair system be able to distinguish in order to tell which nucleotide of a mismatched pair to replace?

Accepted Answer

The mismatch repair system must be able to distinguish between the newly-made strand and the parental strand in order to replace the correct nucleotide of the mismatched pair. This is because during DNA replication, the parental strand serves as a template for the newly-made strand, and any errors in base pairing will result in a mismatch between the two strands. Therefore, the mismatch repair system must be able to differentiate between the two strands to correctly identify which nucleotide needs to be replaced. The other answer choices are not relevant to the process of mismatch repair.

Question 8

DNA sequences comprising the yeast origin of replication can be removed from yeast cells and inserted into bacterial DNA molecules. Because these sequences promote replication of the DNA in which they are contained, they are referred to as __________. (Select all correct choices)

Accepted Answer

Autonomous replicating sequences (ARSs) are DNA sequences that allow a DNA molecule to replicate independently. In yeast, ARSs are essential for the initiation of DNA replication.

Question 9

Which DNA repair mechanism recognizes a distortion in double helix geometry caused by DNA polymerase's insertion of an incorrect nucleotide during replication, one that escaped the enzyme's proofreading exonuclease?

Accepted Answer

Mismatch repair is the DNA repair mechanism that recognizes a distortion in double helix geometry caused by DNA polymerase's insertion of an incorrect nucleotide during replication, one that escaped the enzyme's proofreading exonuclease. Mismatch repair can distinguish the newly synthesized strand from the parental strand and selectively remove and replace the mispaired nucleotide. Nucleotide excision repair deals with larger lesions caused by environmental factors like UV radiation, while base excision repair deals with smaller lesions caused by chemical modifications to individual bases. Double-strand breakage repair and transcription-coupled pathways are not directly related to the issue of misincorporated nucleotides during replication.

Question 10

What enzyme cleaves the DNA backbone to remove the beheaded deoxyribose phosphate during base excision repair?

Accepted Answer

An AP (apurinic/apyrimidinic) endonuclease cleaves the DNA backbone to remove the beheaded deoxyribose phosphate during base excision repair.

Question 11

What happens once damage caused by lesions in the genome, like a thymidine dimer, is bypassed during replication and replication continues?

Accepted Answer

Once damage such as a thymidine dimer is bypassed during replication, the normal replicative DNA polymerase resumes its function and continues replication. This process involves a switch back from the specialized bypass (translesion) DNA polymerase to the regular replicative polymerase.

Question 12

What was the term used to describe the involvement of the public in determining useful mutations in plants derived from gamma garden seed production?

Accepted Answer

The term used to describe the involvement of the public in determining useful mutations in plants derived from gamma garden seed production is citizen science. Citizen science involves the active participation of non-professional scientists in scientific research, which can involve anything from data collection to analysis and interpretation. In this case, the public is involved in identifying useful mutations in plants, which can then be developed further for agricultural purposes. This type of engagement is becoming increasingly popular as a way to involve the public in scientific research and increase scientific literacy. Options A, B, and D are not relevant to the described scenario.

Question 13

What enzyme is responsible for recognizing a chemical alteration in the DNA and removing the base by cleavage of the bond holding the base to the deoxyribose sugar moiety?

Accepted Answer

DNA glycosylase is responsible for recognizing a chemical alteration in the DNA and removing the base by cleavage of the bond holding the base to the deoxyribose sugar moiety.

Question 14

In mammalian cells, a complex of proteins binds to the broken ends of the DNA duplex and catalyzes a series of reactions that rejoin the broken strands. This is an example of what kind of repair?

Accepted Answer

The repair process described involves the joining of broken ends of DNA strands, which is known as nonhomologous end joining. The other options listed (nucleotide excision repair, base excision repair, and mismatch repair) involve the recognition and removal of damaged or incorrect nucleotides from the DNA strand, rather than joining broken ends.

Question 15

Which of these crops is NOT a product of the gamma garden experiments?

Accepted Answer

The gamma garden experiments did not produce Golden Rice.

Question 16

Which eukaryotic DNA polymerases require a sliding clamp to tether the DNA to the polymerase? (Select all correct choices)

Accepted Answer

Polymerase δ and polymerase ε require a sliding clamp to tether the DNA to the polymerase. Polymerase α and polymerase β do not require a sliding clamp, and polymerase ɤ is found only in mitochondria and is not involved in chromosomal DNA replication.

Question 17

The DNA polymerases is a relatively large family of polymerases in which each member is specialized for incorporating nucleotides opposite particular types of DNA lesions in the template strand engage in a type of DNA synthesis called __________. They have an unusually spacious active site that ____________.

Accepted Answer

The DNA polymerases specialized for translesion synthesis have an unusually spacious active site that is able to physically accommodate altered nucleotides that would not fit in the active site of a replicative polymerase. This allows them to continue DNA synthesis past certain types of lesions in the template strand.

Question 18

Why did natural selection favor the use of thymine as a base in DNA instead of uracil even though uracil was presumably present in RNA, when it served as the genetic material during the early evolution of life?

Accepted Answer

Thymine is used in DNA instead of uracil because cytosine can deaminate to form uracil, which would lead to mutations if uracil were a normal component of DNA. Using thymine allows cells to recognize and repair such mutations.

Quiz 13: Dna Replication and Repair