Biochemistry Chapter 9 – DNA Manipulation &
Molecular Biology Exam Review Questions
Verified and Complete with A+ Graded
Rationales Latest Updated 2026
What are restriction enzymes and what do they accomplish?
Restriction endonucleases are bacterial enzymes that recognize specific palindromic DNA
sequences and cleave both strands at or near those sites. They enable precise cutting and
recombination of DNA fragments, which is essential for recombinant DNA technology.
How does a host DNA protect its own DNA from restriction enzymes?
Host bacterial DNA is protected by methylation of its own restriction sites. The addition of
methyl groups prevents recognition and cleavage by the cell's own restriction enzymes.
Understand electrophoresis of DNA.
Gel electrophoresis separates DNA fragments by size. Negatively charged DNA migrates
toward the positive electrode through an agarose matrix, with smaller fragments traveling
faster. This allows visualization, purification, and analysis of DNA fragments.
What does DNA ligase do?
DNA ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides,
sealing breaks in the sugar-phosphate backbone. It is used to join DNA fragments and create
recombinant DNA molecules.
How do these processes work?
Restriction enzymes cut DNA into defined fragments, electrophoresis separates them by size,
and DNA ligase rejoins selected fragments into new combinations. Together, these steps
enable cloning, mapping, and gene analysis.
DNA fingerprinting
DNA fingerprinting uses restriction digestion or PCR amplification of variable DNA regions
(like VNTRs) to create unique fragment patterns for individuals. It is used in forensics,
paternity testing, and genetic identification.
Southern blot
, The Southern blot identifies specific DNA sequences. DNA fragments separated by
electrophoresis are transferred to a membrane and hybridized with a labeled complementary
DNA probe to detect the target sequence.
What are restriction fragment length polymorphisms (RFLPs)? How are they related to
diseases? How are they related to forensic analysis?
RFLPs are inherited variations in DNA fragment lengths caused by sequence changes that alter
restriction sites. They can indicate disease-linked mutations when patterns differ between
normal and mutant alleles, and they provide unique genetic "fingerprints" for forensic
identification.
How are DNA probes and genes synthesized in the lab?
DNA probes are short synthetic DNA sequences complementary to a target region and labeled
radioactively or fluorescently. Genes can be synthesized in vitro by assembling
oligonucleotides or by reverse-transcribing mRNA into cDNA, enabling cloning and sequence
detection.
What is PCR? How does it work? What does it accomplish?
Polymerase Chain Reaction (PCR) amplifies specific DNA sequences exponentially through
repeated cycles of denaturation (strand separation), primer annealing, and extension by heat-
stable DNA polymerase. It produces millions of copies of a target DNA from a tiny initial
sample.
What is recombinant DNA? How is it formed?
Recombinant DNA is a hybrid DNA molecule formed by cutting DNA from different sources
with the same restriction enzyme and joining the fragments with DNA ligase into a vector for
propagation in a host organism.
What are cloning vectors? What are the different types? How do they work?
Cloning vectors are carrier DNA molecules used to transfer foreign DNA into host cells.
Common types include plasmids (small circular DNA), bacteriophages, cosmids, and artificial
chromosomes (BACs, YACs). They contain origins of replication, selectable markers, and
restriction sites to allow cloning and amplification of inserted DNA.
How can you determine which cells contain modified DNA?
Cells containing recombinant DNA are identified using selectable markers (such as antibiotic
resistance genes) or screening systems like blue-white selection, colony hybridization, or PCR
confirmation of inserted DNA.
Molecular Biology Exam Review Questions
Verified and Complete with A+ Graded
Rationales Latest Updated 2026
What are restriction enzymes and what do they accomplish?
Restriction endonucleases are bacterial enzymes that recognize specific palindromic DNA
sequences and cleave both strands at or near those sites. They enable precise cutting and
recombination of DNA fragments, which is essential for recombinant DNA technology.
How does a host DNA protect its own DNA from restriction enzymes?
Host bacterial DNA is protected by methylation of its own restriction sites. The addition of
methyl groups prevents recognition and cleavage by the cell's own restriction enzymes.
Understand electrophoresis of DNA.
Gel electrophoresis separates DNA fragments by size. Negatively charged DNA migrates
toward the positive electrode through an agarose matrix, with smaller fragments traveling
faster. This allows visualization, purification, and analysis of DNA fragments.
What does DNA ligase do?
DNA ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides,
sealing breaks in the sugar-phosphate backbone. It is used to join DNA fragments and create
recombinant DNA molecules.
How do these processes work?
Restriction enzymes cut DNA into defined fragments, electrophoresis separates them by size,
and DNA ligase rejoins selected fragments into new combinations. Together, these steps
enable cloning, mapping, and gene analysis.
DNA fingerprinting
DNA fingerprinting uses restriction digestion or PCR amplification of variable DNA regions
(like VNTRs) to create unique fragment patterns for individuals. It is used in forensics,
paternity testing, and genetic identification.
Southern blot
, The Southern blot identifies specific DNA sequences. DNA fragments separated by
electrophoresis are transferred to a membrane and hybridized with a labeled complementary
DNA probe to detect the target sequence.
What are restriction fragment length polymorphisms (RFLPs)? How are they related to
diseases? How are they related to forensic analysis?
RFLPs are inherited variations in DNA fragment lengths caused by sequence changes that alter
restriction sites. They can indicate disease-linked mutations when patterns differ between
normal and mutant alleles, and they provide unique genetic "fingerprints" for forensic
identification.
How are DNA probes and genes synthesized in the lab?
DNA probes are short synthetic DNA sequences complementary to a target region and labeled
radioactively or fluorescently. Genes can be synthesized in vitro by assembling
oligonucleotides or by reverse-transcribing mRNA into cDNA, enabling cloning and sequence
detection.
What is PCR? How does it work? What does it accomplish?
Polymerase Chain Reaction (PCR) amplifies specific DNA sequences exponentially through
repeated cycles of denaturation (strand separation), primer annealing, and extension by heat-
stable DNA polymerase. It produces millions of copies of a target DNA from a tiny initial
sample.
What is recombinant DNA? How is it formed?
Recombinant DNA is a hybrid DNA molecule formed by cutting DNA from different sources
with the same restriction enzyme and joining the fragments with DNA ligase into a vector for
propagation in a host organism.
What are cloning vectors? What are the different types? How do they work?
Cloning vectors are carrier DNA molecules used to transfer foreign DNA into host cells.
Common types include plasmids (small circular DNA), bacteriophages, cosmids, and artificial
chromosomes (BACs, YACs). They contain origins of replication, selectable markers, and
restriction sites to allow cloning and amplification of inserted DNA.
How can you determine which cells contain modified DNA?
Cells containing recombinant DNA are identified using selectable markers (such as antibiotic
resistance genes) or screening systems like blue-white selection, colony hybridization, or PCR
confirmation of inserted DNA.
