Rucete ✏ AP Biology In a Nutshell
16. Biotechnology — Practice Questions
This chapter covers key biotechnological tools and methods such as bacterial transformation, gel electrophoresis, PCR, and CRISPR-Cas9, explaining their principles and applications in research, medicine, and forensics.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following is used to cut DNA at specific base pair sequences?
(A) DNA ligase
(B) Gel electrophoresis
(C) Polymerase chain reaction
(D) Restriction enzymes
Answer
(D) — Restriction enzymes (restriction endonucleases) cut DNA at specific sequences, allowing targeted DNA manipulation.
2. A forensic scientist recovers a very small amount of DNA evidence at a crime scene. Which technique should be used to amplify the DNA?
(A) Bacterial transformation
(B) CRISPR-Cas9
(C) Gel electrophoresis
(D) Polymerase chain reaction
Answer
(D) — PCR rapidly amplifies specific DNA fragments, making millions of copies from tiny samples.
3. What tool should be used to separate DNA fragments by size after cutting with restriction enzymes?
(A) Bacterial transformation
(B) CRISPR-Cas9
(C) Gel electrophoresis
(D) Polymerase chain reaction
Answer
(C) — Gel electrophoresis separates DNA fragments based on size using an electric current through a gel matrix.
4. Which enzyme should a scientist use to insert the human growth hormone gene into a plasmid?
(A) Bacterial transformation
(B) DNA ligase
(C) Gel electrophoresis
(D) Polymerase chain reaction
Answer
(B) — DNA ligase joins DNA fragments by forming covalent bonds between sugar-phosphate backbones.
5. What method should be used to insert the recombinant plasmid into a bacterial cell?
(A) Bacterial transformation
(B) CRISPR-Cas9
(C) Gel electrophoresis
(D) Polymerase chain reaction
Answer
(A) — Bacterial transformation allows cells to absorb plasmid DNA, often using heat shock to create temporary pores.
6. Which of the following is a key application of gel electrophoresis?
(A) Cutting DNA at specific sequences
(B) Synthesizing proteins
(C) Separating DNA fragments by length
(D) Inserting plasmids into bacterial cells
Answer
(C) — Gel electrophoresis is used to separate DNA fragments based on size, with smaller fragments moving faster through the gel.
7. What is the function of primers in a PCR reaction?
(A) Cut the DNA at specific points
(B) Provide starting points for DNA polymerase
(C) Label DNA fragments with dyes
(D) Restrict DNA replication to specific cells
Answer
(B) — Primers are short DNA sequences that bind to the target region and guide DNA polymerase to begin replication.
8. Which of the following is NOT required for a typical PCR reaction?
(A) DNA polymerase
(B) Primers
(C) Restriction enzymes
(D) Nucleotides
Answer
(C) — PCR requires primers, DNA polymerase, and nucleotides, but restriction enzymes are not used in PCR.
9. What characteristic of DNA causes it to move through a gel during electrophoresis?
(A) Its large size
(B) Its negative charge
(C) Its double-stranded structure
(D) Its helical shape
Answer
(B) — DNA’s phosphate backbone gives it a negative charge, which causes it to move toward the positive electrode in gel electrophoresis.
10. What is a plasmid?
(A) A viral enzyme
(B) A short segment of RNA
(C) A circular DNA molecule used in genetic engineering
(D) A large protein-coding chromosome
Answer
(C) — Plasmids are small, circular DNA molecules often used as vectors in bacterial transformation.
11. What makes the CRISPR-Cas9 system unique compared to traditional restriction enzymes?
(A) It digests proteins
(B) It requires heat shock
(C) It can be programmed to target any DNA sequence
(D) It separates DNA fragments by size
Answer
(C) — CRISPR-Cas9 uses a guide RNA to direct Cas9 to a specific DNA sequence, allowing for precise gene editing.
12. Which of the following techniques is most useful for comparing DNA samples in a paternity test?
(A) CRISPR
(B) Gel electrophoresis
(C) DNA ligase
(D) Bacterial transformation
Answer
(B) — Gel electrophoresis can compare DNA fragment patterns between individuals, commonly used in paternity and forensic analysis.
13. What is the main goal of recombinant DNA technology?
(A) Prevent mutations
(B) Create entirely synthetic chromosomes
(C) Combine DNA from different sources into one molecule
(D) Copy entire genomes in a test tube
Answer
(C) — Recombinant DNA technology allows scientists to join DNA from two different organisms to create new genetic combinations.
14. Which of the following best describes the function of DNA ligase in recombinant DNA work?
(A) Amplifies DNA sequences
(B) Cuts plasmids open
(C) Joins fragments of DNA together
(D) Inserts DNA into bacterial chromosomes
Answer
(C) — DNA ligase is used to covalently bond the sugar-phosphate backbones of DNA fragments.
15. Which type of organism is most commonly used in genetic engineering for producing insulin?
(A) Viruses
(B) Yeast
(C) E. coli bacteria
(D) Amoebas
Answer
(C) — Genetically engineered E. coli are often used to produce human insulin by inserting the insulin gene into a plasmid.
16. Why is a heat-stable DNA polymerase used in PCR reactions?
(A) It denatures DNA strands
(B) It resists contamination
(C) It remains active at high temperatures needed for DNA denaturation
(D) It increases mutation rates
Answer
(C) — Taq polymerase, used in PCR, remains stable at high temperatures required for denaturation steps.
17. What is one reason CRISPR-Cas9 is considered more advanced than traditional gene editing tools?
(A) It only works in prokaryotes
(B) It uses large protein complexes
(C) It allows precise, programmable gene editing with RNA guidance
(D) It creates random mutations
Answer
(C) — CRISPR-Cas9 uses guide RNAs to target specific DNA sequences for precise cutting and editing.
18. In biotechnology, what is a “vector”?
(A) A protein that cuts DNA
(B) A carrier used to transfer foreign DNA into a cell
(C) A sequence that marks the start of transcription
(D) A piece of RNA used in translation
Answer
(B) — A vector, such as a plasmid or virus, is used to deliver genetic material into a host cell.
19. What allows restriction enzymes to cut DNA at the same place every time?
(A) They recognize specific amino acid sequences
(B) They are attracted to promoter regions
(C) They bind to specific nucleotide recognition sequences
(D) They move randomly along DNA until they stop
Answer
(C) — Restriction enzymes recognize specific short DNA sequences and always cut at or near those sites.
20. Which term describes the process of inserting foreign DNA into a bacterial plasmid and then into a bacterial cell?
(A) DNA ligation
(B) Recombinant insertion
(C) Bacterial transformation
(D) Gene expression
Answer
(C) — Bacterial transformation refers to the uptake of plasmid DNA containing foreign genes by a bacterial cell.
21. What does PCR stand for?
(A) Protein Cloning Reaction
(B) Plasmid Construction Replication
(C) Polymerase Chain Reaction
(D) Phosphorylation Control Response
Answer
(C) — PCR stands for Polymerase Chain Reaction, a method to amplify DNA sequences.
22. Which of the following statements about CRISPR is true?
(A) It uses proteins from eukaryotes
(B) It was originally discovered as a bacterial immune system
(C) It binds only to RNA sequences
(D) It randomly mutates DNA
Answer
(B) — CRISPR is based on a natural system used by bacteria to recognize and cut foreign DNA from viruses.
23. Why is it important to use multiple identical DNA samples in a gel electrophoresis test?
(A) It prevents degradation
(B) It makes bands brighter
(C) It ensures reliable comparison between samples
(D) It ensures faster replication
Answer
(C) — Using replicates increases the accuracy of results by controlling for experimental variability.
24. Which of the following is a major benefit of using recombinant DNA technology in agriculture?
(A) Faster gel electrophoresis
(B) Cloning of livestock
(C) Production of crops resistant to pests or drought
(D) Generating artificial embryos
Answer
(C) — Genetically engineered crops can be designed for resistance to pests, disease, or environmental stress.
25. What makes the Cas9 protein an essential component of CRISPR gene editing?
(A) It synthesizes guide RNA
(B) It binds directly to ribosomes
(C) It cuts DNA at the targeted site
(D) It copies the DNA sequence for analysis
Answer
(C) — Cas9 is an endonuclease that creates double-stranded breaks at specific sites determined by guide RNA.
26. A researcher wants to determine the size of DNA fragments produced by restriction enzyme digestion. Which factor most directly affects how far each fragment moves during gel electrophoresis?
(A) DNA sequence
(B) DNA polarity
(C) DNA fragment length
(D) Concentration of DNA polymerase
Answer
(C) — Shorter DNA fragments move farther through the gel matrix; fragment length directly influences migration distance.
27. A scientist wants to inactivate a specific gene in a living eukaryotic cell using biotechnology. Which method is best suited for this purpose?
(A) Gel electrophoresis
(B) CRISPR-Cas9 with a guide RNA
(C) Heat shock and transformation
(D) PCR amplification with primers
Answer
(B) — CRISPR-Cas9 uses a guide RNA to target and create a double-stranded break in specific genes, allowing for inactivation or editing.
28. What is the primary role of the guide RNA in CRISPR-Cas9 gene editing?
(A) It cuts the target DNA
(B) It helps DNA ligase function
(C) It directs Cas9 to a complementary DNA sequence
(D) It stabilizes mRNA after editing
Answer
(C) — The guide RNA pairs with the target DNA sequence, guiding the Cas9 nuclease to the correct site for cleavage.
29. Why is Taq polymerase particularly useful in PCR reactions?
(A) It amplifies RNA instead of DNA
(B) It binds only to plasmids
(C) It remains stable at high temperatures used in DNA denaturation steps
(D) It inserts genes into bacterial cells
Answer
(C) — Taq polymerase is heat-resistant, making it ideal for the repeated heating and cooling cycles of PCR.
30. In CRISPR-Cas9, what occurs immediately after Cas9 introduces a double-stranded break in the DNA?
(A) The cell replicates the break
(B) The gene is deleted permanently
(C) The cell attempts to repair the break, which can lead to insertion or deletion mutations
(D) The DNA ligase immediately fixes the break without error
Answer
(C) — Double-stranded breaks often undergo imperfect repair, leading to insertions or deletions that disrupt gene function.
31. Why is the use of a selectable marker (e.g., antibiotic resistance gene) important in bacterial transformation experiments?
(A) It prevents plasmid replication
(B) It identifies bacteria that took up the recombinant plasmid
(C) It amplifies foreign DNA sequences
(D) It regulates transcription in human genes
Answer
(B) — Selectable markers allow only transformed cells (e.g., antibiotic-resistant ones) to survive and grow on selective media.
32. A DNA fragment was inserted into a plasmid but the bacteria failed to express the gene. Which of the following is a likely explanation?
(A) The DNA was cut by PCR
(B) The fragment was inserted in the reverse orientation
(C) The gel concentration was too low
(D) The DNA was too small to detect
Answer
(B) — If the inserted gene is in the wrong orientation, transcription may not proceed properly, preventing gene expression.
33. A researcher uses restriction enzymes to cut two different DNA samples and then mixes and ligates them. What ensures that only recombinant plasmids are selected in transformed bacteria?
(A) Use of electrophoresis
(B) Presence of a selectable marker in the plasmid
(C) Use of a heat-stable polymerase
(D) Activation of CRISPR in the plasmid
Answer
(B) — A selectable marker (e.g., antibiotic resistance) allows identification of bacteria that have taken up the plasmid, whether or not recombination was successful.
34. What distinguishes recombinant DNA from naturally occurring DNA?
(A) It is single-stranded
(B) It originates from a single organism
(C) It combines DNA from two or more sources into one molecule
(D) It only exists in RNA viruses
Answer
(C) — Recombinant DNA combines genetic material from different sources into a single functional molecule.
35. Why is PCR a critical step before gel electrophoresis in many DNA analysis protocols?
(A) It digests proteins
(B) It increases the amount of DNA available for visualization
(C) It turns RNA into DNA
(D) It edits the DNA sequence
Answer
(B) — PCR amplifies DNA, providing enough material for detection and analysis during electrophoresis.
36. Explain how CRISPR-Cas9 can be used to correct a genetic disorder caused by a point mutation.
Answer
CRISPR-Cas9 uses a guide RNA to target the mutated gene, and Cas9 introduces a double-stranded break. A corrected DNA template can be provided for the cell to use during repair, allowing the point mutation to be replaced via homology-directed repair.
37. Describe how gel electrophoresis can be used to compare genetic similarity between individuals.
Answer
By cutting DNA with restriction enzymes and running it through a gel, the resulting band patterns can be compared. Similar banding patterns indicate genetic similarity, while differences suggest variations in DNA sequences.
38. A mutation occurs in the recognition site for a restriction enzyme. How might this affect a gel electrophoresis analysis?
Answer
The enzyme may no longer cut at that site, resulting in larger or fewer DNA fragments, which will change the expected band pattern in the gel.
39. What role does heat shock play in bacterial transformation protocols?
Answer
Heat shock temporarily opens pores in the bacterial membrane, allowing plasmid DNA to enter the cell more easily.
40. Why is it important to use DNA from a known source as a control during gel electrophoresis?
Answer
The control provides a reference for fragment size and ensures the gel ran correctly. It also helps verify the identity or integrity of unknown samples by comparison.
41. How does the specificity of guide RNA in the CRISPR system enhance its usefulness in biotechnology?
Answer
Guide RNA can be custom-designed to match nearly any DNA sequence, allowing researchers to target and edit specific genes with high precision.
42. Describe one ethical concern associated with the use of CRISPR gene editing in human embryos.
Answer
Editing embryos can lead to permanent changes in the germline, raising concerns about unintended consequences, designer babies, and the long-term impact on future generations.
43. Why are plasmids commonly used as vectors in genetic engineering?
Answer
Plasmids can replicate independently of the host genome, are easy to manipulate, and can carry foreign genes into bacterial cells for expression.
44. A student adds DNA samples to a gel but no bands appear after running electrophoresis. List one possible reason for this error.
Answer
The DNA samples may not have been stained with a dye like ethidium bromide or SYBR Green, making the fragments invisible under UV light.
45. What is the purpose of using a thermal cycler in PCR?
Answer
A thermal cycler automates the temperature changes required for DNA denaturation, primer annealing, and extension during each PCR cycle.
46. How can PCR be used in diagnosing infectious diseases?
Answer
PCR can detect the presence of pathogen-specific DNA or RNA in a patient sample, confirming infection even at low concentrations.
47. A DNA sample produces two distinct bands after electrophoresis. What does this suggest about the DNA?
Answer
It indicates that the sample contains two different fragment sizes, possibly due to partial digestion or multiple DNA sources.
48. How do restriction enzymes recognize where to cut DNA?
Answer
They bind to specific short palindromic nucleotide sequences, called recognition sites, and cleave the DNA at or near those sequences.
49. Why is CRISPR-Cas9 often more efficient than using restriction enzymes in gene editing?
Answer
CRISPR-Cas9 can be programmed to target any sequence using guide RNA, whereas restriction enzymes require naturally occurring recognition sites and cannot be redirected easily.
50. A scientist wants to express a human gene in bacteria. Outline the basic steps using recombinant DNA technology.
Answer
First, isolate the gene and insert it into a plasmid vector using restriction enzymes and ligase. Next, transform bacteria with the recombinant plasmid. Finally, grow the bacteria to express and harvest the protein.