MCQOPTIONS
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MCQOPTIONS
This section includes 62 Mcqs, each offering curated multiple-choice questions to sharpen your DNA Sequencing, Mutation and Repair knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The fragments of DNA are joined together by which of the following enzymes? |
| A. | Endonuclease |
| B. | DNA polymerase |
| C. | Primase |
| D. | Ligase |
| Answer» E. | |
| 2. |
In a cross between two heterozygous (Aa), results will be: |
| A. | in the ratio 1:3 homozygous to heterozygous |
| B. | in the ratio 1:1 homozygous to heterozygous |
| C. | in the ratio 1 :3 heterozygous to homozygous |
| D. | all heterozygous |
| Answer» C. in the ratio 1 :3 heterozygous to homozygous | |
| 3. |
In crossing a homozygous recessive with a heterozygote, what is the chance of getting an offspring with the homozygous recessive phenotype? |
| A. | 75% |
| B. | 25% |
| C. | 50% |
| D. | 0% |
| Answer» D. 0% | |
| 4. |
When a gene for a given trait comes in alternative versions that specify different forms of the trait (for example, purple-flower and white-flower versions of a flower color gene), the versions of the gene are called |
| A. | loci |
| B. | supergenes |
| C. | chromosomes |
| D. | alleles |
| Answer» E. | |
| 5. |
In a given organism, how do cells at completion of meiosis compare with cells that are just about to begin meiosis? |
| A. | They have half the number of chromosomes and one-fourth the amount of DNA. |
| B. | They have half the amount of cytoplasm and twice the amount of DNA. |
| C. | They have twice the amount of cytoplasm and half the amount of DNA. |
| D. | They have the same number of chromosomes and half the amount of DNA. |
| Answer» B. They have half the amount of cytoplasm and twice the amount of DNA. | |
| 6. |
An allele that is fully expressed is referred to as (fully expressed means that the allele is transcribed and translated into a perfectly functional protein) |
| A. | dominant |
| B. | recessive |
| C. | homologous |
| D. | heterozygous |
| Answer» B. recessive | |
| 7. |
The word homologous literally means same location. How does this relate to homologous chromosomes? |
| A. | All of the below are correct. |
| B. | The bands resulting from staining are found in the same location. |
| C. | The chromosomes have the same genes in the same location. |
| D. | Both B and C are correct. |
| Answer» E. | |
| 8. |
It is difficult to observe individual chromosomes with a light microscope during prophase because |
| A. | the DNA has not been replicated yet. |
| B. | they are uncoiled in long, thin strands. |
| C. | they leave the nucleus and are dispersed to other parts of the cell. |
| D. | sister chromatids do not pair up until division starts. |
| Answer» C. they leave the nucleus and are dispersed to other parts of the cell. | |
| 9. |
How do the daughter cells at the end of mitosis and cytokinesis compare with their parent cell when it was in G1 of the cell cycle? |
| A. | The daughter cells will have half the amount of cytoplasm and half the amount of DNA. |
| B. | The daughter cells will have half the number of chromosomes and half the amount of DNA. |
| C. | The daughter cells will have the same number of chromosomes and half the amount of DNA. |
| D. | The daughter cells will have the same number of chromosomes and the same amount of DNA. |
| Answer» E. | |
| 10. |
Cytokinesis usually, but not always, follows mitosis. If cells undergo mitosis and not cytokinesis, this would result in |
| A. | a cell with a single large nucleus |
| B. | a cell with two nuclei. |
| C. | cells with abnormally small nuclei |
| D. | feedback responses that prevent mitosis |
| Answer» C. cells with abnormally small nuclei | |
| 11. |
A base substitution mutation in a gene sometimes has no effect on the protein the gene codes for. Which of the following factors could account for this? |
| A. | the rarity of such mutations |
| B. | some amino acids have more than one codon |
| C. | a correcting mechanism that is part of the mRNA molecule |
| D. | A and B |
| Answer» C. a correcting mechanism that is part of the mRNA molecule | |
| 12. |
The 3 5 phosphodiester linkage joins |
| A. | two DNA strands |
| B. | two nucleotides |
| C. | a nitrogenous base with pentose sugar |
| D. | two nucleosides |
| Answer» C. a nitrogenous base with pentose sugar | |
| 13. |
Association of histones H1 with nucleosome shows |
| A. | the occurrence of transcription |
| B. | the occurrence of replication |
| C. | exposed DNA double helix |
| D. | the condensation of DNA into chromatin fibre |
| Answer» E. | |
| 14. |
Termination of replication is triggered by |
| A. | DNA polymerase |
| B. | Helicase |
| C. | SSB |
| D. | Tus protein |
| Answer» E. | |
| 15. |
DNA polymerase synthesizes |
| A. | DNA in 5 -3 direction |
| B. | DNA in 3 -5 direction |
| C. | mRNA in 3 -5 direction |
| D. | mRNA in 5 -3 direction |
| Answer» B. DNA in 3 -5 direction | |
| 16. |
Which of the following is used in DNA replication studies? |
| A. | Neurospora crassa |
| B. | Drosophila melanogaster |
| C. | Escherichia coli |
| D. | Pneumococcus |
| Answer» D. Pneumococcus | |
| 17. |
Which of the following helps in opening of DNA double helix in front of replication fork? |
| A. | topoisomerase |
| B. | DNA polymerase-I |
| C. | DNA gyrase |
| D. | DNA ligase |
| Answer» D. DNA ligase | |
| 18. |
DNA replication is |
| A. | conservative |
| B. | conservative and discontinuous |
| C. | semi-conservative and discontinuous |
| D. | semi-conservative and semi-discontinuous |
| Answer» E. | |
| 19. |
Which of the following enzymes separates the two strands of DNA during replication? |
| A. | Gyrase |
| B. | Topoisomerase |
| C. | Helicase |
| D. | DNA polymerase |
| Answer» D. DNA polymerase | |
| 20. |
During replication, Okazaki fragments elongate |
| A. | leading strand towards the replication fork |
| B. | lagging strand towards the replication fork |
| C. | leading strand away from the replication fork |
| D. | lagging strand away from the replication fork |
| Answer» E. | |
| 21. |
Any change in the nucleotide sequence of the DNA of a gene is called |
| A. | a mutation. |
| B. | an advantage. |
| C. | a codon. |
| D. | an anticodon. |
| Answer» B. an advantage. | |
| 22. |
Which, if any, of the following statements is incorrect? |
| A. | Each person makes many millions of different HLA proteins so as to be able to recognize and bind foreign antigens. |
| B. | Classical HLA proteins are highly polymorphic; non-classical HLA proteins show very limited polymorphism. |
| C. | Classical class I HLA proteins are displayed on the surface of very few cell types, notably immune system cells. |
| D. | HLA proteins are the most polymorphic human proteins |
| Answer» B. Classical HLA proteins are highly polymorphic; non-classical HLA proteins show very limited polymorphism. | |
| 23. |
Which of the following is NOT a DNA repair mechanism? |
| A. | Binding-protein excision repair |
| B. | Base excision repair |
| C. | Nucleotide excision repair |
| D. | Mismatch repair |
| Answer» B. Base excision repair | |
| 24. |
Classical class I and class II HLA proteins are both highly polymorphic heterodimers polymorphic heterodimers that help lymphocytes to recognize peptide antigens but they differ in many ways. Which, if any of the following statements, is true? |
| A. | The two chains of any class I HLA protein are made by genes that are located on different chromosomes. |
| B. | Each of the two protein chains of a classical class I HLA protein are highly polymorphic, unlike for classical class II HLA proteins where only one of the protein chains is polymorphic |
| C. | Class I HLA proteins assist helper T lymphocytes to recognize peptide antigens, whereas class II HLA proteins assist cytotoxic T lymphocytes to recognize peptide antigens. |
| D. | Class II HLA proteins are expressed on the surfaces of almost all nucleated cells, but the expression of class I HLA proteins is confined to just a few types of cell, notably certain immune system cells. |
| Answer» B. Each of the two protein chains of a classical class I HLA protein are highly polymorphic, unlike for classical class II HLA proteins where only one of the protein chains is polymorphic | |
| 25. |
What, approximately, is the fraction of genetic variation in the nuclear genome is that is expected to have a harmful effect on gene function? |
| A. | 50%. |
| B. | 25%. |
| C. | 10% |
| D. | 1%. |
| Answer» E. | |
| 26. |
With reference to aberrant methylation of bases which of the following statements, if any, is false? |
| A. | S-adenosylmethionine donates methyl groups to a range of different molecules in cells and frequently inappropriately methylates bases in DNA. |
| B. | Guanine is occasionally methylated to give O-6-methylguanine which base pairs with adenine rather than with cytidine. |
| C. | In each nucleated cell, about 300-600 adenines are converted to 3-methyladenine per day. |
| D. | 3-methyladenine can be a cytotoxic base: it distorts the double helix and that can disrupt crucial DNA-protein interactions. |
| Answer» C. In each nucleated cell, about 300-600 adenines are converted to 3-methyladenine per day. | |
| 27. |
With reference to hydrolytic damage to DNA which of the following statements, if any, is false? |
| A. | Hydrolytic attack commonly causes cleavage of the N-glycosidic bond, resulting in loss of bases. |
| B. | Loss of pyrimidines is particularly common. |
| C. | Hydrolytic attack also commonly causes amino groups to be stripped from bases (deamination). |
| D. | Cytosines are often deaminated to give thymines. |
| Answer» C. Hydrolytic attack also commonly causes amino groups to be stripped from bases (deamination). | |
| 28. |
With reference to DNA repair, which of the following statements, if any, is false? |
| A. | In the great majority of cases, DNA repair is some kind of mechanism that does not directly reverse the molecular steps that cause DNA damage. |
| B. | Most of the time DNA repair involves a mechanism that makes a repair to both DNA strands. |
| C. | When DNA repair involves repairing both DNA strands, the accuracy of the repair is higher in cells where the DNA has replicated than in cells before DNA replication. |
| D. | DNA repair mechanisms are not evolutionarily well-conserved; human repair mechanisms differ significantly from those in the cells of other vertebrates. |
| Answer» B. Most of the time DNA repair involves a mechanism that makes a repair to both DNA strands. | |
| 29. |
With reference to base cross-linking, which, if any, of the following statements, is false? |
| A. | Base cross-linking means that covalent bonds form between two bases. |
| B. | The cross-linked bases are on opposing DNA strands. |
| C. | The anti-cancer agent cisplatin causes a type of cross-linking between two guanine residues. |
| D. | Pyrimidine dimers are a type of base cross-linking that is commonly induced by excess exposure to sunlight. |
| Answer» C. The anti-cancer agent cisplatin causes a type of cross-linking between two guanine residues. | |
| 30. |
Which, if any, of the following statements is false? |
| A. | Most of the inherited changes in our DNA arise because of exposure to extracellular mutagens, including radiation sources and chemical mutagens |
| B. | Most of the inherited changes in our DNA arise because of unavoidable endogenous errors in cellular mechanisms and harmful effects of certain natural molecules and atoms within our cells. |
| C. | Errors in DNA replication and DNA repair are a major source of mutations in our cells |
| D. | Significant chemical damage is sustained by DNA because of its proximity to water molecules in our cells. |
| Answer» B. Most of the inherited changes in our DNA arise because of unavoidable endogenous errors in cellular mechanisms and harmful effects of certain natural molecules and atoms within our cells. | |
| 31. |
The enzyme photolyase is used in what method of repair? |
| A. | Base excision |
| B. | Photo reactivation |
| C. | Nucleotide excision |
| D. | None of the mentioned |
| Answer» C. Nucleotide excision | |
| 32. |
What is the relationship among DNA, a gene, and a chromosome? |
| A. | A chromosome contains hundreds of genes, which are composed of DNA. |
| B. | A chromosome contains hundreds of genes, which are composed of protein. |
| C. | A gene contains hundreds of chromosomes, which are composed of protein. |
| D. | A gene is composed of DNA, but there is no relationship to a chromosome. |
| Answer» B. A chromosome contains hundreds of genes, which are composed of protein. | |
| 33. |
Recombinational repair is often due to ____________ |
| A. | Incorporation of many incorrect nucleotides by DNA pol |
| B. | Many cystidine dimer and associated large gaps in a strand |
| C. | Many thymidine dimer formations and associated large gaps in a strand |
| D. | All of the mentioned |
| Answer» D. All of the mentioned | |
| 34. |
A point mutation that replaces a purine with another purine, or a pyrimidine with another pyramidine ____________ |
| A. | Nonsense mutation |
| B. | Silent mutation |
| C. | Transition mutation |
| D. | Transversion |
| Answer» D. Transversion | |
| 35. |
The enzyme of E.coli is a nuclease that initiates the repair of double stranded DNA breaks by homologous recombination is? |
| A. | DNA glycosylase |
| B. | DNA ligase |
| C. | DNA polymerase |
| D. | RNA polymerase |
| Answer» B. DNA ligase | |
| 36. |
Which of the following enzymes is not involved in the process of replicating DNA in a replication bubble? |
| A. | Ligase |
| B. | Methyltransferase |
| C. | Primase |
| D. | Polymerase |
| Answer» C. Primase | |
| 37. |
Which enzyme is responsible for removing the RNA primers added during DNA replication? |
| A. | DNA polymerase I |
| B. | Primase |
| C. | DNA polymerase III |
| D. | DNA ligase |
| Answer» B. Primase | |
| 38. |
Magnesium is a necessary component of DNA polymerization, but is not found in the DNA molecule. What is the purpose of magnesium in the polymerization of DNA? |
| A. | None of these answers are correct |
| B. | It is a cofactor for DNA polymerase III |
| C. | It binds to the two leaving groups during the DNA polymerization reaction |
| D. | It binds nucleotides in the cytosol and helps import them into the nucleus |
| Answer» D. It binds nucleotides in the cytosol and helps import them into the nucleus | |
| 39. |
What 3' functional group must be free in order to add the next nucleotide during DNA synthesis? |
| A. | Amine |
| B. | Carboxylic acid |
| C. | Phosphate |
| D. | Hydroxyl |
| Answer» E. | |
| 40. |
During DNA replication, single-stranded DNA is kept from reannealing due to the function of __________. |
| A. | histones |
| B. | DNA topoisomerase |
| C. | single-strand binding proteins |
| D. | helicase |
| Answer» D. helicase | |
| 41. |
What is the role of helicase? |
| A. | Prevents DNA strands from reannealing |
| B. | Nicks the DNA backbone to relieve supercoils |
| C. | Unwinds DNA template at the replication fork |
| D. | Facilitates formation of phosphodiester bonds |
| Answer» D. Facilitates formation of phosphodiester bonds | |
| 42. |
__________ is the primary prokaryotic replicatory polymerase that can proofread DNA and fix incorrect base pairs due to its __________. |
| A. | DNA polymerase III . . . 3'-5' exonuclease function |
| B. | DNA polymerase III . . . 3'-5' endonuclease function |
| C. | DNA polymerase I . . . 3'-5' endonuclease function |
| D. | DNA polymerase I . . . 3'-5' exonuclease function |
| Answer» B. DNA polymerase III . . . 3'-5' endonuclease function | |
| 43. |
Which of the following structures indicates where DNA replication begins? |
| A. | Helicase |
| B. | DNA polymerase III |
| C. | Replication fork |
| D. | Origin of replication |
| Answer» E. | |
| 44. |
Which of the following enzymes adds DNA to the ends of chromosomes to avoid loss of genetic material with duplication? |
| A. | Primase |
| B. | Helicase |
| C. | Telomerase |
| D. | Polymerase |
| Answer» D. Polymerase | |
| 45. |
Branched nucleic acid structures containing 4 double-stranded arms that are intermediates in genetic recombination and DNA repair are best known as? |
| A. | Pyrimidine dimers |
| B. | None of these |
| C. | Spliceosome |
| D. | Holliday junction |
| Answer» E. | |
| 46. |
What term best describes when RNA polymerase binds promoters and synthesizes and releases short mRNA transcripts in cycles before the RNA holoenzyme leaves the promoter? |
| A. | Cyclic initiation |
| B. | Abortive initiation |
| C. | Repressive transcription |
| D. | DNA scrunching |
| Answer» C. Repressive transcription | |
| 47. |
Which of the following DNA repair mechanisms would be employed by the cell to repair DNA damage from UV light? |
| A. | None of these answers are correct |
| B. | Base excision repair |
| C. | Nucleotide excision repair |
| D. | Direct reversal |
| Answer» D. Direct reversal | |
| 48. |
If a double strand break (DSB) is not repaired during G1 phase of the cell cycle, what type of replication error would result during S phase at the site of the DSB? |
| A. | Reversed replication fork |
| B. | Catenane formations |
| C. | Collapsed replication fork |
| D. | Gap in the newly replicated DNA strand |
| Answer» D. Gap in the newly replicated DNA strand | |
| 49. |
What is translesion DNA synthesis? |
| A. | A method of RNA synthesis used to make highly specialized RNA molecules |
| B. | A method of DNA synthesis used exclusively for the mitochondrial genome |
| C. | A method of DNA synthesis by which a cell may replicate over a mutation encountered on the parental strand |
| D. | A method of DNA synthesis used by prokaryotes only |
| Answer» D. A method of DNA synthesis used by prokaryotes only | |
| 50. |
Primase is an enzyme that synthesize small primers for DNA polymerase to bind to so it can initiate DNA replication. What are these primers made of? |
| A. | DNA |
| B. | RNA |
| C. | Carbohydrates |
| D. | Lipids |
| Answer» C. Carbohydrates | |