Molecular Biology and Genomics Practice Questions

Q: In DNA replication, which enzyme synthesizes RNA primers?

Primase. ### ***Primase*** - **Primase** is an **RNA polymerase** that synthesizes short **RNA primers** (approximately 10-12 nucleotides long) to provide a free **3'-OH group** needed by **DNA polymerase** to initiate synthesis. - Without this primer, **DNA replication** cannot begin because **DNA polymerases** lack the ability to start synthesizing a new strand *de novo*. *Topoisomerase* - **Topoisomerases** (such as **DNA gyrase**) are responsible for relieving **supercoiling** and **torsional strain** in the DNA helix ahead of the replication fork. - They do not possess **primase** activity and do not participate in synthesizing the RNA primer. *DNA polymerase II* - **DNA polymerase II** is primarily involved in **DNA repair** mechanisms, specifically in replicating through damaged DNA segments. - It lacks the catalytic ability to synthesize RNA primers and is not a replication initiator. *DNA polymerase III* - **DNA polymerase III** is the primary enzyme responsible for the **elongation** of the leading and lagging strands, adding nucleotides to the existing primer. - While it is essential for synthesizing the bulk of the new DNA, it requires a preexisting primer to function and cannot generate one itself.

Q: Which molecular biotechnology is depicted in the image shown below:

CRISPR-Cas9 gene editing system. ***CRISPR-Cas9 gene editing system*** - This system utilizes a **guide RNA (gRNA)** to direct the **Cas9 endonuclease** to a specific complementary DNA sequence, creating a double-strand break. - It is a highly versatile and precise tool used for **genome editing**, enabling gene knockouts, insertions, or corrections by leveraging cellular repair mechanisms like **non-homologous end joining (NHEJ)** or **homology-directed repair (HDR)**. *Microarray analysis* - This technique involves hybridizing fluorescently labeled cDNA or cRNA samples to a chip containing thousands of **immobilized DNA probes**. - It is primarily used for **gene expression profiling** or genotyping, rather than inducing specific genetic alterations. *In situ hybridization* - This method uses labeled **DNA or RNA probes** to detect the presence and location of specific nucleic acid sequences within intact cells or tissues. - It is used for **diagnostic imaging of gene expression** or chromosomal abnormalities and does not involve gene editing activity. *DNA sequencing* - This process determines the exact **nucleotide order** of a DNA fragment, such as via the **Sanger method** or **next-generation sequencing (NGS)**. - It is a purely observational tool for reading genetic information and lacks the capacity to physically modify or cut genomic DNA.

Question 1

In DNA replication, which enzyme synthesizes RNA primers?

Accepted Answer

Primase

Answer

Topoisomerase

Answer

DNA polymerase II

Answer

DNA polymerase III

Question 2

Which molecular biotechnology is depicted in the image shown below:

Accepted Answer

CRISPR-Cas9 gene editing system

Answer

Microarray analysis

Answer

In situ hybridization

Answer

DNA sequencing

Question 3

A research team is developing a gene therapy approach using CRISPR-Cas9 to correct a point mutation causing sickle cell disease. They must decide between two strategies: (A) correcting the mutation in hematopoietic stem cells ex vivo, or (B) in vivo correction in bone marrow. Considering molecular physiology principles, what is the most significant advantage of strategy A over strategy B?

Accepted Answer

Strategy A allows for screening and selection of successfully edited cells before transplantation, minimizing off-target effects

Answer

Strategy A requires lower doses of viral vectors

Answer

Strategy A produces faster clinical improvement

Answer

Strategy A is less expensive to implement

Question 4

How does alternative splicing contribute to protein diversity in humans despite having approximately 20,000 genes?

Accepted Answer

By allowing different combinations of exons to be included in mature mRNA

Answer

By modifying amino acids after translation

Answer

By changing the sequence of codons in the mRNA

Answer

By producing different tRNA molecules

Question 5

Why does DNA replication occur in a 5' to 3' direction only?

Accepted Answer

Because DNA polymerase can only add nucleotides to the 3'-OH group

Answer

Because primase can only synthesize primers in that direction

Answer

Because the template strand is read in 3' to 5' direction only

Answer

Because helicase unwinds DNA in only one direction

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

On this page

Practice by Chapter

Want unlimited practice?