Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics Indian Medical PG Practice Questions and MCQs

Question 841: Jumping gene is a type of what?

A. Transposon (Correct Answer)
B. Episome
C. Cosmid
D. Plasmid

Explanation: ***Transposon*** - A **transposon** is a segment of DNA that can **change its position within a genome**, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. - The term **"jumping gene"** is a colloquial and descriptive name for a transposon, reflecting its ability to move or "jump" from one location to another. *Episome* - An **episome** is a **plasmid** that can exist either as an independent cytoplasmic entity or as a **segment integrated into the host cell's chromosome**. - While it can integrate into the genome, its primary definition is an extrachromosomal genetic element, not a moving DNA sequence itself. *Cosmid* - A **cosmid** is a type of **hybrid plasmid** that contains **cos sequences** (cohesive ends) from the lambda phage. - They are primarily used as cloning vectors for very large DNA inserts and do not inherently "jump" within the genome. *Plasmid* - A **plasmid** is a **small, extrachromosomal DNA molecule** within a cell that is physically separated from chromosomal DNA and can replicate independently. - While plasmids can be transferred between bacteria, they are not typically referred to as "jumping genes" because they don't move within the host genome.

Question 842: Mutations are due to changes in:

A. DNA nucleotide sequence (Correct Answer)
B. RNA nucleotide sequence
C. Amino acid sequence of ribonuclease
D. Cell membrane

Explanation: ***DNA nucleotide sequence*** - **Mutations** are defined as changes in the **genetic material**, which is primarily composed of **DNA**. - These changes in the **nucleotide sequence** of DNA can alter the genetic code, leading to changes in **protein structure and function**. *RNA nucleotide sequence* - While RNA can have its nucleotide sequence altered, these changes are generally not considered true **mutations** in the heritable sense for most organisms. - RNA is typically a temporary molecule, and changes to its sequence are usually not passed down to subsequent generations. *Amino acid sequence of ribonuclease* - An altered **amino acid sequence** in a protein like ribonuclease is a consequence of a **mutation in the DNA**, not the mutation itself. - **Ribonucleases** are enzymes that catalyze the degradation of RNA, and their structure is determined by the **DNA sequence**. *Cell membrane* - The cell membrane is a **lipid bilayer** with embedded proteins that regulates cellular transport and communication. - While its components can be affected by genetic mutations, alterations in the cell membrane itself do not constitute the primary definition of a **mutation**.

Question 843: Which statement is false regarding the LAC OPERON MODEL?

A. A gene= GALACTOSIDE ACETYLASE
B. PROMOTER IS A TRANS ACTING FACTOR (Correct Answer)
C. Y gene = GALACTOSIDE PERMEASE
D. CAMP-CAP COMPLEX IS A POSITIVE REGULATOR

Explanation: ***PROMOTER IS A TRANS ACTING FACTOR*** - A **promoter** is a region of DNA that initiates transcription of a particular gene. It is a **cis-acting element**, meaning it influences the expression of genes on the same DNA molecule. - **Trans-acting factors** are molecules (like proteins) that can diffuse through the cell and act on any DNA molecule, not just the one they were transcribed from. *CAMP-CAP COMPLEX IS A POSITIVE REGULATOR* - The **cAMP-CAP complex** (also known as the **cAMP-CRP complex**) binds to the promoter region of the *lac* operon and **activates transcription** when glucose levels are low and lactose is present. - This binding enhances the affinity of RNA polymerase for the promoter, thus acting as a **positive regulator** of gene expression. *Y gene = GALACTOSIDE PERMEASE* - The ***lacY* gene** in the *lac* operon codes for **galactoside permease**. - Galactoside permease is responsible for transporting **lactose into the bacterial cell**. *A gene= GALACTOSIDE ACETYLASE* - The ***lacA* gene** in the *lac* operon codes for **galactoside acetylase** (**thiogalactoside transacetylase**). - This enzyme's precise physiological role in lactose metabolism is **not fully understood**, but it may help detoxify cells by acetylating non-metabolizable galactosides.

Question 844: Which of the following does not undergo genetic recombination during gametogenesis?

A. X chromosome
B. Y chromosome
C. Autosome 21
D. Mitochondrial chromosome (Correct Answer)

Explanation: ***Mitochondrial chromosome*** - The **mitochondrial chromosome** is inherited exclusively from the mother and **does not undergo any genetic recombination** during gametogenesis. - Its transmission is **clonal** and follows a maternal lineage, making it useful for tracking maternal ancestry. - Unlike nuclear chromosomes, there is **complete absence of recombination** in mitochondrial DNA. *X chromosome* - The **X chromosome** undergoes **recombination** during female meiosis (oogenesis) between homologous X chromosomes. - In males, there is limited recombination between the X and Y chromosomes in the **pseudoautosomal regions (PARs)**. *Y chromosome* - The **Y chromosome** undergoes **limited recombination** only in the **pseudoautosomal regions (PARs)**, which comprise ~5% of the chromosome. - The **majority (~95%)** of the Y chromosome, including the **sex-determining region Y (SRY)** and male-specific region (MSY), is paternally inherited **without recombination**. - However, since some recombination does occur at PARs, the Y chromosome is not the best answer for "does not undergo genetic recombination." *Autosome 21* - **Autosomes**, including chromosome 21, undergo extensive **genetic recombination** during both male and female meiosis. - This process of **crossing over** between homologous chromosomes is crucial for generating genetic diversity in offspring.

Question 845: Which of the following statements accurately describes a gene library?

A. A physical library containing books about genetics.
B. A digital database of genetic sequences.
C. A collection of cloned DNA fragments that represent an organism's genome. (Correct Answer)
D. A collection of DNA sequences or fragments.

Explanation: ***A collection of cloned DNA fragments that represent an organism's genome.*** - A **gene library** (also called a DNA library) is a collection of various **DNA fragments** from a genome, each carried by a vector and cloned in a host cell, so that the entire genome is represented and can be accessed. - This systematic collection ensures that essentially all the organism's **genetic material** is available for study, screening, and sequencing. *A physical library containing books about genetics.* - This statement describes a traditional **resource for genetic information**, not the molecular construct itself. - A physical library contains **printed materials** (books, journals) for reading and research, distinct from biological samples. *A digital database of genetic sequences.* - While digital databases store genetic sequence information (e.g., GenBank), they are **in silico** representations and not physical collections of DNA. - These databases are used to **analyze and retrieve genetic information**, but they are not the gene libraries themselves. *A collection of DNA sequences or fragments.* - This definition is too broad, as a gene library specifically refers to **cloned DNA fragments**. - Without the cloning and representation of an entire genome, it's merely a collection, not a structured "library" in the molecular biology sense.

Question 846: In the mammalian genome, the maximum number of genes code for the receptors of what?

A. Interleukin receptors
B. Growth factor receptors
C. Olfactory receptors (Correct Answer)
D. Immunoglobulin receptors (antibodies)

Explanation: ***Olfactory receptors*** - The mammalian genome dedicates an unusually large number of genes, often hundreds or even over a thousand, to **olfactory receptors**, reflecting the diversity of odors an animal can detect. - This extensive gene family allows for the recognition of a vast array of odorant molecules, crucial for survival functions like finding food, avoiding predators, and reproduction. *Interleukin receptors* - While important for immune function, the number of genes coding for **interleukin receptors** is significantly smaller than that for olfactory receptors. - They are involved in specific immune cell signaling, not the broad sensory detection found in olfaction. *Growth factor receptors* - **Growth factor receptors** play vital roles in cell growth, differentiation, and metabolism, but the gene family size is much more limited compared to olfactory receptors. - Their functions are highly regulated and typically involve a smaller set of ligands. *Immunoglobulin receptors (antibodies)* - The diversity of **antibodies** is generated primarily through **somatic recombination** and **hypermutation**, not by a massive number of germline genes coding for individual receptors. - The germline genes for immunoglobulins are organized into gene segments that rearrange, rather than having a unique gene for each potential antibody specificity.

Question 847: Which of the following techniques is primarily used for RNA analysis?

A. Sanger's technique
B. Western blot
C. Next generation sequencing (Correct Answer)
D. PCR

Explanation: ***Next generation sequencing*** - **Next-generation sequencing (NGS)**, particularly RNA-Seq, is widely used for **transcriptome analysis** to quantify and discover RNA molecules. - RNA-Seq allows for the precise measurement of **gene expression levels**, identification of **novel transcripts**, and detection of **splicing variants**. *Sanger's technique* - **Sanger sequencing** is primarily used for **DNA sequencing** to determine the exact order of nucleotides in a DNA molecule. - While it can be applied to cDNA (synthesized from RNA), it is not directly used for **RNA analysis** itself. *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 and then transferring them to a membrane for antibody-based detection, making it unsuitable for direct **RNA analysis**. *PCR* - **Polymerase Chain Reaction (PCR)** is used to amplify specific **DNA sequences**. - While **Reverse Transcription PCR (RT-PCR)** can quantify RNA by first converting it to cDNA, PCR itself does not directly analyze the RNA molecule.

Practice by Chapter

DNA Replication and Repair Mechanisms

Practice Questions

Transcription Factors and Gene Regulation

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Epigenetics and DNA Methylation

Practice Questions

RNA Processing and Splicing

Practice Questions

miRNA and RNA Interference

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Protein Synthesis and Post-Translational Modifications

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Genomics and Human Genome Project

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Single Nucleotide Polymorphisms

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Gene Therapy Approaches

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CRISPR-Cas9 and Genome Editing

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DNA Fingerprinting and Forensics

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Molecular Basis of Genetic Diseases

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