STP Genomics & Molecular Biology 1 — Questions and Answers
Question 1: Which enzyme is primarily responsible for synthesizing new DNA strands during replication in eukaryotes?
- DNA Polymerase α
- DNA Polymerase δ (Correct answer)
- RNA Polymerase II
- Reverse transcriptase
Correct answer: DNA Polymerase δ
DNA Polymerase δ is the main replicative polymerase responsible for synthesizing the lagging and leading strands during eukaryotic DNA replication.
Question 2: What is the primary purpose of the polymerase chain reaction (PCR) in a clinical laboratory setting?
- To sequence an entire genome
- To amplify a specific DNA or RNA target for detection or analysis (Correct answer)
- To measure gene expression levels directly
- To determine protein structure from nucleotide sequence
Correct answer: To amplify a specific DNA or RNA target for detection or analysis
PCR amplifies a defined region of nucleic acid exponentially, enabling detection or downstream analysis even from minute sample quantities.
Question 3: A single nucleotide polymorphism (SNP) is best described as:
- A large chromosomal deletion affecting multiple genes
- A variation in a single base pair at a specific locus occurring in ≥1% of the population (Correct answer)
- An insertion of a transposable element into a coding region
- A change in the number of chromosomal copies
Correct answer: A variation in a single base pair at a specific locus occurring in ≥1% of the population
SNPs are the most common form of genetic variation, defined as a single base change at a given genomic position present in at least 1% of the population.
Question 4: In gel electrophoresis of DNA, smaller fragments migrate:
- Towards the negative electrode (cathode)
- More slowly than larger fragments
- Faster and further from the wells than larger fragments (Correct answer)
- At the same rate regardless of size if voltage is constant
Correct answer: Faster and further from the wells than larger fragments
The negatively charged DNA migrates towards the positive electrode, and smaller fragments experience less resistance in the gel matrix, moving faster and further.
Question 5: Which molecular technique uses sequence-specific probes to detect target DNA within intact chromosomal preparations?
- Southern blotting
- Fluorescence in situ hybridisation (FISH) (Correct answer)
- Comparative genomic hybridisation (CGH)
- Quantitative PCR (qPCR)
Correct answer: Fluorescence in situ hybridisation (FISH)
FISH uses fluorescently labelled probes that hybridise to complementary sequences on chromosomes, allowing visual detection of specific loci or structural rearrangements.
Question 6: Restriction endonucleases are most commonly used in molecular biology to:
- Remove RNA primers during DNA replication
- Cleave double-stranded DNA at specific recognition sequences (Correct answer)
- Join DNA fragments together in cloning procedures
- Synthesise complementary DNA from an RNA template
Correct answer: Cleave double-stranded DNA at specific recognition sequences
Restriction endonucleases recognise specific palindromic sequences and cleave both DNA strands, generating fragments used in cloning, mapping, and diagnostic applications.
Question 7: Next-generation sequencing (NGS) differs from Sanger sequencing primarily in that it:
- Uses dideoxynucleotide chain terminators to determine base sequence
- Can sequence millions of DNA fragments simultaneously in a massively parallel manner (Correct answer)
- Requires substantially more template DNA than first-generation methods
- Produces longer individual reads than any first-generation method
Correct answer: Can sequence millions of DNA fragments simultaneously in a massively parallel manner
NGS platforms perform massively parallel sequencing of millions of clonally amplified fragments simultaneously, drastically increasing throughput and reducing per-base cost compared to Sanger sequencing.
STP Genomics & Molecular Biology 1
Which enzyme is primarily responsible for synthesizing new DNA strands during replication in eukaryotes?