1.
Which epigenetic modification involves the addition of an acetyl group to histone proteins?
Correct Answer
A. Histone methylation
Explanation
Histone acetylation involves the addition of an acetyl group to specific lysine residues on histone proteins, typically found in the histone tails. This modification neutralizes the positive charge of histones, weakening the interaction between histones and DNA. As a result, chromatin adopts a more relaxed, open conformation, making DNA more accessible to transcription factors and RNA polymerase. This facilitates gene expression by promoting the transcription of genes located in regions with acetylated histones.
2.
What is the primary function of DNA methyltransferase enzymes in epigenetics?
Correct Answer
A. Adding methyl groups to DNA
Explanation
DNA methylation is a covalent modification that involves the addition of a methyl group to the 5' carbon of cytosine residues, primarily occurring in the context of CpG dinucleotides. DNA methyltransferase enzymes catalyze this reaction, transferring methyl groups from S-adenosyl methionine (SAM) to cytosine bases. DNA methylation is essential for gene regulation, genomic imprinting, X-chromosome inactivation, and maintaining genomic stability.
3.
Which enzyme is responsible for removing acetyl groups from histone proteins?
Correct Answer
C. Histone deacetylase
Explanation
Histone deacetylase enzymes catalyze the removal of acetyl groups from lysine residues on histone proteins, leading to chromatin condensation and transcriptional repression. By removing acetyl groups, histone deacetylases restore the positive charge of histones, strengthening the interaction between histones and DNA. This results in the compaction of chromatin structure, making it less accessible to transcriptional machinery and inhibiting gene expression.
4.
In genetic engineering, what is the purpose of a selectable marker in a plasmid vector?
Correct Answer
A. To indicate successful transformation
Explanation
Selectable markers, such as antibiotic resistance genes or fluorescent proteins, are incorporated into plasmid vectors used for genetic engineering. These markers allow researchers to easily identify and select cells that have successfully taken up the recombinant DNA (e.g., a plasmid containing a gene of interest). For example, in bacterial transformation experiments, cells containing the vector with the selectable marker can grow in the presence of an antibiotic, indicating successful transformation.
5.
What is the name of the process in which a piece of DNA is inserted into a vector to create a recombinant DNA molecule?
Correct Answer
D. DNA cloning
Explanation
DNA cloning is a technique used to create multiple copies of a specific DNA fragment by inserting it into a vector, such as a plasmid or a viral genome. This process typically involves digesting both the DNA fragment and the vector with restriction enzymes, followed by ligation of the DNA fragments into the vector using DNA ligase. The recombinant DNA molecule is then introduced into a host organism, where it can replicate and produce multiple copies of the inserted DNA fragment.
6.
Which of the following is NOT a component of the CRISPR-Cas9 system?
Correct Answer
C. DNA ligase
Explanation
DNA ligase is an enzyme that catalyzes the formation of phosphodiester bonds between adjacent nucleotides in DNA molecules. In genetic engineering, DNA ligase is used to join together DNA fragments, such as the gene of interest and a plasmid vector, to create a recombinant DNA molecule. This enzyme seals the nicks in the sugar-phosphate backbone of DNA, resulting in a continuous DNA strand that can be replicated and expressed in a host organism.
7.
What is the purpose of a reporter gene in genetic engineering experiments?
Correct Answer
B. To identify transformed cells
Explanation
Reporter genes, also known as marker genes, are genes that are genetically engineered to produce a detectable signal, such as fluorescence or enzymatic activity, when expressed in a cell. In genetic engineering experiments, reporter genes are often co-expressed with the gene of interest and used to identify cells that have successfully taken up the recombinant DNA. The presence of the reporter gene allows researchers to easily identify and select transformed cells for further analysis.
8.
What is the role of DNA ligase in genetic engineering?
Correct Answer
A. Joining DNA fragments together
Explanation
DNA ligase plays a crucial role in genetic engineering by catalyzing the formation of phosphodiester bonds between the 3' hydroxyl end of one DNA fragment and the 5' phosphate end of another DNA fragment. This process, known as ligation, joins together DNA fragments to create a recombinant DNA molecule. DNA ligase is essential for sealing nicks or gaps in the sugar-phosphate backbone of DNA, ensuring the integrity and stability of the recombinant DNA molecule.
9.
How does RNA interference (RNAi) technology work in genetic engineering?
Correct Answer
D. By silencing gene expression post-transcriptionally
Explanation
RNA interference (RNAi) is a mechanism that regulates gene expression post-transcriptionally by targeting mRNA molecules for degradation or translational repression. Small RNA molecules, such as small interfering RNA (siRNA) or microRNA (miRNA), guide the RNA-induced silencing complex (RISC) to complementary sequences in the target mRNA. The RISC complex then cleaves the mRNA or inhibits its translation, leading to gene silencing. RNAi technology is widely used in genetic engineering to knock down gene expression, study gene function, and develop therapeutic interventions.
10.
What is the purpose of bisulfite sequencing in epigenetic research?
Correct Answer
A. To detect DNA methylation patterns
Explanation
Bisulfite sequencing is a technique used to analyze DNA methylation patterns at single-nucleotide resolution. Bisulfite treatment converts unmethylated cytosine residues to uracil, while methylated cytosines remain unchanged. Following bisulfite treatment, DNA is sequenced, and the converted cytosines are detected as thymine residues. By comparing the sequences of treated and untreated DNA samples, researchers can identify methylated cytosines and map DNA methylation patterns across the genome. Bisulfite sequencing is a powerful tool for studying epigenetic modifications and their role in gene regulation and disease.