Molecular Biology and Genomics Practice Questions

Q: How many PCR cycles are needed to produce half the amplified DNA copies produced by 27 cycles of PCR?

26. ***26 (Correct)*** - PCR amplification follows an **exponential growth** pattern, where the template DNA is theoretically doubled in each cycle. The product quantity is proportional to 2^n (where n is the cycle number). - If 27 cycles produce 2^27 copies, half of this amount is calculated as 2^27 / 2, which mathematically simplifies to 2^(27-1). Therefore, exactly **26 cycles** are needed. *25 (Incorrect)* - 25 cycles would produce 2^25 copies. Since 2^27 = 4 × 2^25, 25 cycles yield only **one-quarter** (25%) of the DNA produced by 27 cycles, not half. - In exponential amplification, a difference of two cycles corresponds to a **four-fold change** in product amount. *13 (Incorrect)* - 13 cycles would produce 2^13 copies, which represents an extremely small fraction of the total DNA generated after 27 cycles (2^27). - This amount belongs to the early phase of the reaction and is mathematically too low to be relevant to the calculation for half the **final product quantity**. *12 (Incorrect)* - 12 cycles produce 2^12 copies, which is 2^15 times less than 2^27 copies. - This number is irrelevant as it doesn't align with the required calculation based on the principles of **geometric progression** in PCR.

Q: A frameshift mutation occurs due to the insertion of a new nucleotide at the 4th position of an mRNA sequence with 900 nucleotides. What is the most likely outcome of this mutation?

Partial protein production. ***Partial protein production*** - The insertion of a single nucleotide at position 4 causes a **frameshift mutation**, which fundamentally alters the reading frame starting from the second codon. - Frameshift mutations typically lead to the introduction of a **Premature Termination Codon (PTC)** shortly downstream, resulting in the synthesis of a **truncated** (partial) and non-functional protein. *No change in the final protein* - A change from position 4 onward affects almost the entire coding sequence; thus, there cannot be **no change** in the protein structure. - Only an insertion/deletion of a multiple of three nucleotides (in-frame mutation) or a mutation late in the sequence might result in a preserved protein function. *Complete change in protein production* - While the subsequent mRNA sequence is entirely changed, the outcome on the protein level is usually **truncation** (partial protein), not the complete synthesis of a full-length, completely altered protein. - The term "complete change" is less accurate than "partial production," as the protein synthesis is typically **aborted prematurely**. *No protein production* - The **start codon** (positions 1-3) is upstream of the mutation site (position 4) and remains intact, allowing for **translation initiation** to occur normally. - Protein production starts; it is only terminated prematurely when a stop codon is encountered in the shifted reading frame.

Q: The law stating that "the relative frequencies of each gene allele tend to remain constant from generation to generation" is known as

Hardy-Weinberg Law. ***Hardy-Weinberg Law*** - The **Hardy-Weinberg principle** states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. - This law provides a baseline for understanding how populations evolve by identifying the conditions under which evolution *does not* occur. *Lamarck's Law* - **Lamarck's theory of inheritance of acquired characteristics** suggested that traits acquired during an organism's lifetime could be passed on to offspring. - This concept is largely disproven and not relevant to allele frequency constancy across generations. *David-Morgan's Law* - This is not a recognized law in genetics. There was a prominent geneticist named **Thomas Hunt Morgan**, whose work focused on fruit flies and established the **chromosome theory of inheritance** and concepts like linkage and crossing over. - While significant to genetics, his work does not describe the constancy of allele frequencies in a population. *Mendel's Law* - **Mendel's Laws of Inheritance** (segregation and independent assortment) describe how traits are passed from parents to offspring through the inheritance of discrete units (genes). - While fundamental to explaining inheritance, they do not directly state that allele frequencies remain constant in a population across generations under specific conditions, as the Hardy-Weinberg law does.

Q: Which of the following correctly describes gene therapy ?

Introduction of gene sequence into a cell. ***Introduction of gene sequence into a cell*** - **Gene therapy** fundamentally involves the **delivery of genetic material** (DNA or RNA) into a patient's cells to treat or prevent disease. - The goal is to correct a **genetic defect**, provide a new therapeutic function, or alter gene expression for a desired outcome. *Mapping and isolation of gene sequence* - While essential steps in understanding and preparing for gene therapy, **mapping and isolation** alone do not constitute the therapy itself. - These processes are preliminary research activities to identify the target gene and its location. *Synthesis of DNA probes with specific sequence* - **DNA probes** are short, single-stranded DNA or RNA sequences used to detect the presence of complementary nucleic acid sequences. - Their synthesis is a technique used in **molecular diagnostics** and research, not gene therapy, which aims to introduce functional genes. *Use of polymerase chain reaction technique* - **PCR** is a molecular biology technique used to amplify a specific segment of DNA, creating many copies. - It is a tool for **diagnosis**, research, and sometimes in the preparation of genetic material for therapy, but it is not gene therapy itself.

Q: Which of the following is used to detect abnormal gene sequences EXCEPT?

Flow cytometry. ***Flow cytometry*** - **Flow cytometry** is primarily used to analyze **cell populations** based on their physical and biochemical characteristics (e.g., size, granularity, and protein expression) by passing them single file through a laser beam, not for direct gene sequencing. - It detects and quantifies cells labeled with **fluorescent antibodies**, making it useful for immunophenotyping, cell sorting, and DNA content analysis, but not for identifying specific gene sequences or mutations. *RFLP analysis* - **Restriction fragment length polymorphism (RFLP) analysis** detects variations in **DNA sequences** by using **restriction enzymes** to cut DNA at specific sites. - Differences in fragment lengths indicate **polymorphisms** or **mutations** within the recognition sites, thereby identifying abnormal gene sequences. *Pyrosequencing* - **Pyrosequencing** is a method of **DNA sequencing** that determines the sequence of nucleotides by detecting the release of pyrophosphate during DNA synthesis. - It is used to identify **single nucleotide polymorphisms (SNPs)** and **short genetic variations**, making it suitable for detecting abnormal gene sequences. *FISH* - **Fluorescence in situ hybridization (FISH)** uses **fluorescently labeled DNA probes** that bind to specific complementary **DNA sequences** on chromosomes. - It is a powerful cytogenetic technique for detecting **chromosomal abnormalities**, such as deletions, translocations, and amplifications, thereby identifying abnormal gene sequences.

Q: DNA sequence is determined by?

Sanger sequencing. ***Correct: Sanger sequencing*** - **Sanger sequencing** (chain-termination method) is the gold standard technique used to determine the exact order of nucleotides within a DNA molecule - It uses dideoxynucleotides (ddNTPs) to terminate DNA strand elongation at specific bases, producing fragments of varying lengths - These fragments are separated by capillary electrophoresis and the sequence is read based on the terminal fluorescent label - Directly determines DNA sequence with high accuracy *Incorrect: PCR* - **Polymerase Chain Reaction (PCR)** amplifies specific DNA segments to create millions of copies - It does NOT determine the sequence itself - it only makes copies of DNA - PCR-amplified DNA can be used as a template for subsequent sequencing, but PCR itself doesn't reveal sequence information *Incorrect: FISH* - **Fluorescence in situ hybridization (FISH)** detects and localizes specific DNA sequences on chromosomes - Used for chromosomal mapping and detecting chromosomal abnormalities - Does not determine the nucleotide sequence *Incorrect: Gel electrophoresis* - Separates DNA fragments based on size and charge - Used to analyze DNA but cannot determine the specific nucleotide sequence - Useful for visualizing DNA after amplification or restriction digestion

Q: miRNA binds to which part of the mRNA to inhibit translation?

3'UTR. ***3'UTR*** - MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression. - They primarily bind to the **3' untranslated region (3'UTR)** of messenger RNA (mRNA) molecules, leading to translational repression or mRNA degradation. *Gene promoter* - The **gene promoter** is a region of DNA located upstream of a gene, where regulatory proteins bind to initiate transcription. - miRNAs do not directly bind to gene promoters to inhibit translation. *Gene body* - The **gene body** refers to the entire transcribed region of a gene, including exons and introns. - While some regulatory elements can be found within the gene body, the primary binding site for miRNAs to exert translational control is the 3'UTR. *5'UTR* - The **5' untranslated region (5'UTR)** is located at the 5' end of an mRNA molecule, upstream of the start codon. - While the 5'UTR can play a role in regulating translation initiation, it is not the primary target for miRNA binding to inhibit translation.

Q: What is the repair mechanism associated with CRISPR-cas9?

Non-homologous end joining. ***Non-homologous end joining*** - **CRISPR-Cas9** creates a **double-strand break (DSB)** in DNA, which is primarily repaired by **non-homologous end joining (NHEJ)**. - **NHEJ** is the **predominant repair pathway** in most cells, accounting for 60-90% of DSB repairs. - **NHEJ** is an error-prone repair mechanism that ligates the broken ends directly, often leading to small **insertions or deletions (indels)** causing gene knockout. - Note: **Homology-directed repair (HDR)** is another CRISPR-associated mechanism used for precise editing when a donor template is provided, but **NHEJ is the primary endogenous repair pathway**. *Mismatch repair* - This mechanism corrects errors that arise during **DNA replication**, such as incorrect base pairing. - It does not repair **double-strand breaks** induced by CRISPR-Cas9. *Nucleotide excision repair* - This pathway removes **bulky DNA adducts** and lesions, such as those caused by UV radiation. - It is not involved in repairing **CRISPR-Cas9 induced double-strand breaks**. *Base excision repair* - This mechanism corrects **damaged or modified bases**, typically single base changes, without affecting the sugar-phosphate backbone significantly. - It handles different types of DNA damage than the **double-strand breaks** generated by CRISPR-Cas9.

Q: Which of the following molecular analysis methods is used to detect RNA?

RT-PCR. ***RT-PCR*** - **Reverse transcriptase polymerase chain reaction (RT-PCR)** is a molecular method that first converts **RNA into complementary DNA (cDNA)** using reverse transcriptase before amplification via PCR. - This technique is commonly used to detect and quantify specific **RNA sequences**, such as viral RNA or gene expression levels. *Western blot* - **Western blot** is a laboratory technique used to detect specific **proteins** in a sample. - It involves separating proteins by size using gel electrophoresis, transferring them to a membrane, and then detecting the target protein using specific antibodies. *G banding* - **G banding** is a cytogenetic technique used to produce a visible **karyotype** by staining condensed chromosomes. - This method is primarily used to detect large-scale structural changes in chromosomes, not to detect RNA. *Sanger's method* - **Sanger's method**, also known as **dideoxy sequencing**, is a DNA sequencing technique. - It is used to determine the exact order of **nucleotides within a DNA molecule**, not to detect RNA directly.

Q: Steps of PCR in sequence are?

Denature DNA, Anneal Primers, Extend DNA. ***Denature DNA, Anneal Primers, Extend DNA*** - This sequence represents the three fundamental steps of each PCR cycle, ensuring accurate and efficient **DNA amplification**. - **Denaturation** separates the double-stranded DNA template, **annealing** allows primers to bind to specific sequences, and **extension** synthesizes new DNA strands. *Denature DNA, Extend DNA, Anneal Primers* - This order is incorrect because **primer annealing** must occur before DNA extension can begin. - Primers provide the necessary starting points for the **DNA polymerase** to synthesize the new strands. *Anneal Primers, Extend DNA, Denature DNA* - This sequence is incorrect as the **template DNA** must first be denatured to separate the strands before primers can anneal to them. - If the DNA is not denatured, the primers cannot access their target sequences. *Extend DNA, Anneal Primers, Denature DNA* - This order is incorrect because **DNA extension** is the final step, occurring only after denaturation and primer annealing. - The polymerase requires both a denatured template and bound primers to initiate synthesis.

Question 1

How many PCR cycles are needed to produce half the amplified DNA copies produced by 27 cycles of PCR?

Accepted Answer

26

Answer

12

Answer

25

Answer

13

Question 2

A frameshift mutation occurs due to the insertion of a new nucleotide at the 4th position of an mRNA sequence with 900 nucleotides. What is the most likely outcome of this mutation?

Accepted Answer

Partial protein production

Answer

Complete change in protein production

Answer

No protein production

Answer

No change in the final protein

Question 3

The law stating that "the relative frequencies of each gene allele tend to remain constant from generation to generation" is known as

Accepted Answer

Hardy-Weinberg Law

Answer

Lamarck's Law

Answer

David-Morgan's Law

Answer

Mendel's Law

Question 4

Which of the following correctly describes gene therapy ?

Accepted Answer

Introduction of gene sequence into a cell

Answer

Mapping and isolation of gene sequence

Answer

Synthesis of DNA probes with specific sequence

Answer

Use of polymerase chain reaction technique

Question 5

Which of the following is used to detect abnormal gene sequences EXCEPT?

Accepted Answer

Flow cytometry

Answer

RFLP analysis

Answer

Pyrosequencing

Answer

FISH

Question 6

DNA sequence is determined by?

Accepted Answer

Sanger sequencing

Answer

PCR

Answer

FISH

Answer

Gel electrophoresis

Question 7

miRNA binds to which part of the mRNA to inhibit translation?

Accepted Answer

3'UTR

Answer

Gene promoter

Answer

Gene body

Answer

5'UTR

Question 8

What is the repair mechanism associated with CRISPR-cas9?

Accepted Answer

Non-homologous end joining

Answer

Mismatch repair

Answer

Nucleotide excision repair

Answer

Base excision repair

Question 9

Which of the following molecular analysis methods is used to detect RNA?

Accepted Answer

RT-PCR

Answer

Western blot

Answer

G banding

Answer

Sanger's method

Question 10

Steps of PCR in sequence are?

Accepted Answer

Denature DNA, Anneal Primers, Extend DNA

Answer

Denature DNA, Extend DNA, Anneal Primers

Answer

Anneal Primers, Extend DNA, Denature DNA

Answer

Extend DNA, Anneal Primers, Denature DNA

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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