Molecular Biology and Genomics Practice Questions

Q: The Central Dogma of molecular biology includes all except?

Reverse transcription. ***Reverse transcription*** - The **original Central Dogma** as proposed by Francis Crick described the unidirectional flow of genetic information: **DNA → RNA → Protein**. - **Reverse transcription** (RNA → DNA) was **not part of the original Central Dogma** and was only discovered later with the identification of **reverse transcriptase enzyme** in retroviruses by Baltimore and Temin (1970). - While reverse transcription is now recognized as an important biological process, it represents an **exception to the classical Central Dogma** rather than a core component. *Transcription* - **Transcription** (DNA → RNA) is a **fundamental process** within the Central Dogma. - It involves synthesis of RNA from a DNA template and is the first step in gene expression in all living organisms. *Translation* - **Translation** (RNA → Protein) is the **second major step** of the Central Dogma. - This process occurs on ribosomes where mRNA is decoded into a specific sequence of amino acids to form proteins. *RNA replication* - **RNA replication** (RNA → RNA), while primarily seen in RNA viruses, is considered part of the **expanded Central Dogma**. - It represents one of the possible flows of genetic information in biological systems, though not universal to all organisms.

Q: Function of reverse transcriptase is

RNA dependent DNA synthesis. ***RNA dependent DNA synthesis*** - **Reverse transcriptase** is an enzyme that catalyzes the formation of **DNA from an RNA template**, a process known as reverse transcription. - This function is crucial for **retroviruses** like HIV, which use it to integrate their RNA genome into the host cell's DNA. *DNA dependent RNA synthesis* - This process is known as **transcription**, carried out by **RNA polymerase**. - It involves the synthesis of **RNA from a DNA template**, the opposite of reverse transcription. *DNA dependent DNA synthesis* - This process is known as **DNA replication**, carried out by **DNA polymerase**. - It involves the synthesis of **new DNA strands from existing DNA templates**. *RNA dependent RNA synthesis* - This process is characteristic of **RNA viruses**, specifically those with **RNA replicase** enzymes. - These enzymes synthesize **new RNA strands from an RNA template** for viral replication.

Q: BRCA1 gene is located on which chromosome?

17q21. ***17q21*** - The **BRCA1 gene** is located on the long arm (q) of **chromosome 17** at region 21. - This gene plays a crucial role in **DNA repair** and is associated with an increased risk of breast and ovarian cancers. *13q12* - This location corresponds to the **BRCA2 gene**, which is also involved in DNA repair and cancer predisposition. - While both BRCA1 and BRCA2 are significant, they are distinct genes on different chromosomes. *12q13* - This is not the correct chromosomal location for either BRCA1 or BRCA2. - Various other genes are located on chromosome 12, but not BRCA1. *21q17* - This is an incorrect chromosomal designation; the "q" arm designation is typically followed by a band number, and 17 is not a standard band number for chromosome 21 in this context. - **Chromosome 21** is primarily associated with **Down syndrome** (trisomy 21).

Q: Sumoylation of histone proteins is associated with

Transcription repression. ***Transcription repression*** - **Sumoylation** is a post-translational modification involving the covalent attachment of **Small Ubiquitin-like Modifier (SUMO) proteins** to target proteins, which leads to transcriptional repression. - When histones are sumoylated, it alters chromatin structure and recruits **transcriptional corepressors**, making the DNA less accessible for transcription factors. - This is the **primary and well-established function** of histone sumoylation in gene regulation. *Activation of gene transcription* - **Histone acetylation** and specific methylation patterns (e.g., H3K4me3, H3K36me3) are associated with **transcriptional activation**, not sumoylation. - Sumoylation typically creates a repressive chromatin environment, hindering gene expression. *Condensation of chromosome* - While sumoylation can influence chromatin structure, **chromosome condensation** during cell division is primarily regulated by **condensins** and **cohesins**. - Sumoylation's role in condensation is indirect and not its primary function. *DNA replication* - DNA replication is a separate process from transcriptional regulation and involves DNA polymerases and replication machinery. - Histone sumoylation specifically affects **gene transcription**, not DNA replication.

Q: Which of the following statements about mitochondrial gene inheritance is true?

Mitochondrial genes are inherited from the mother.. ***Mitochondrial genes are inherited from the mother.*** - During fertilization, the **ovum** contributes the vast majority of the cytoplasm, including all the mitochondria, to the zygote. - This results in a distinctive pattern of **maternal inheritance** for mitochondrial DNA (mtDNA); only mothers pass mitochondria to all their offspring. *Mitochondrial gene mutations are inherited in a paternal pattern.* - This statement is incorrect because mitochondrial inheritance is exclusively **maternal**, meaning mutations are passed from the mother, not the father. - Paternal DNA is primarily contained within the nucleus of the sperm head, and very few, if any, paternal mitochondria enter the oocyte during fertilization. *Mitochondrial genes are inherited from the father.* - This is incorrect as mitochondria are almost exclusively inherited from the **mother's ovum**. - The sperm provides its nuclear DNA but typically contributes negligible or no mitochondria to the zygote. *Mitochondrial genes follow Mendelian inheritance.* - Mitochondrial inheritance is **non-Mendelian**; it does not follow the classic dominant/recessive patterns or segregation expected with nuclear genes. - Due to maternal inheritance, all offspring of an affected mother will inherit the mitochondrial condition, regardless of sex.

Q: Which of the following is not a method for introducing a gene into target cells?

FISH. ***FISH*** - **FISH (Fluorescence In Situ Hybridization)** is a cytogenetic technique used to detect and localize the presence or absence of specific **DNA sequences** on chromosomes. - It is an imaging and diagnostic technique, not a method for introducing genetic material into cells. *Electroporation* - **Electroporation** is a physical method that uses an **electric pulse** to create temporary pores in cell membranes. - These temporary pores allow for the direct uptake of **exogenous DNA** (or other molecules) into the cell. *Transfection* - **Transfection** is a general term referring to the process of deliberately introducing **nucleic acids (DNA or RNA)** into eukaryotic cells. - It encompasses various methods, including chemical (e.g., lipid-based), physical (e.g., electroporation), and viral approaches. *Site directed recombination* - **Site-directed recombination** is a molecular biology technique used to introduce **targeted genetic changes** (insertions, deletions, or substitutions) at specific locations in a genome. - This process involves the direct introduction of modified genetic material that then recombines with the host genome.

Q: Which of the following statements is true regarding the role of enzymes in recombinant DNA technology?

DNA ligase is used. ***DNA ligase is used*** - **DNA ligase** plays a crucial role in **recombinant DNA technology** by forming **phosphodiester bonds** to join DNA strands, such as in inserting a gene into a plasmid. - This enzyme is essential for **recombinant DNA formation** by covalently linking compatible sticky or blunt ends of DNA fragments. - DNA ligase catalyzes the final step of **sealing nicks** in the DNA backbone, creating stable recombinant molecules. *Restriction endonucleases are involved* - **Restriction endonucleases** (restriction enzymes) are indeed crucial for **cutting DNA** at specific recognition sites, creating DNA fragments with sticky or blunt ends. - While absolutely essential to the overall process, this statement uses "are involved" which is less specific than "is used" for describing the ligase's direct role in joining fragments. - Both enzymes work sequentially: restriction enzymes cut, then ligase joins. *Acid phosphatase is used* - **Acid phosphatase** is an enzyme found in lysosomes and is involved in **phosphate group removal** from substrates. - It is not used in **recombinant DNA technology** for cutting or joining DNA fragments. *Reverse transcriptase needed* - **Reverse transcriptase** is used to synthesize **cDNA from an mRNA template**, a process known as reverse transcription. - This enzyme is essential for creating **cDNA libraries** but is not directly involved in the core steps of cutting and joining DNA fragments in standard recombinant DNA procedures.

Q: Transition from G2 to M phase of the cell cycle is controlled by which?

Cyclin B. ***Cyclin B*** - The transition from G2 to M phase is primarily controlled by the **maturation-promoting factor (MPF)**, which is a complex of **cyclin B** and **CDK1 (cyclin-dependent kinase 1)**. - **Cyclin B** levels rise during G2 and peak at M phase, activating CDK1 to initiate mitosis. *Retinoblastoma gene product* - The **retinoblastoma (Rb) protein** primarily regulates the G1/S transition by inhibiting the E2F transcription factor. - It acts as a **tumor suppressor**, preventing uncontrolled cell proliferation. *p53 protein* - The **p53 protein** is a critical **tumor suppressor** that monitors DNA integrity at various cell cycle checkpoints, particularly G1/S and G2/M. - If DNA damage is detected, p53 can induce cell cycle arrest and/or apoptosis, but it is not directly responsible for initiating M phase. *Cyclin E* - **Cyclin E** is essential for the **G1/S transition**, forming a complex with CDK2 to initiate DNA replication. - Its activity peaks during late G1 and early S phase, not during the G2/M transition.

Q: Gene amplification is achieved through

Polymerase Chain Reaction. ***Polymerase Chain Reaction*** - **PCR** is the **gold standard** molecular biology technique that generates **millions to billions of copies** of a specific DNA segment over a short period. - It utilizes a cyclical process of **denaturation**, **annealing**, and **extension** with **thermostable DNA polymerase** to achieve exponential amplification. - **Most widely used** method for gene amplification in research and diagnostics. *DNA strand hybridization* - **DNA strand hybridization** is the process where two complementary single-stranded DNA molecules bind together to form a **double-stranded molecule**. - This process is fundamental to many molecular techniques but does not, in itself, achieve **amplification**; rather, it is a **binding event**. *In situ DNA hybridization* - **In situ hybridization** is a technique that localizes and detects specific **nucleic acid sequences** (DNA or RNA) within cells or tissues directly on a slide. - While it uses **hybridization**, its primary purpose is **detection and localization**, not the **amplification** of DNA sequences. *Ligase chain reaction (LCR)* - **LCR** is a molecular technique that does amplify DNA sequences exponentially using **DNA ligase** to join adjacent oligonucleotide probes. - However, it is **less commonly used** than PCR, has more **stringent requirements** (requires knowledge of both strands), and is primarily used for detecting **known point mutations** rather than general gene amplification. - **PCR remains the standard** technique when the question refers to gene amplification without additional qualifiers.

Question 1

The Central Dogma of molecular biology includes all except?

Accepted Answer

Reverse transcription

Answer

Transcription

Answer

RNA replication

Answer

Translation

Question 2

Function of reverse transcriptase is

Accepted Answer

RNA dependent DNA synthesis

Answer

DNA dependent RNA synthesis

Answer

DNA dependent DNA synthesis

Answer

RNA dependent RNA synthesis

Question 3

BRCA1 gene is located on which chromosome?

Accepted Answer

17q21

Answer

13q12

Answer

12q13

Answer

21q17

Question 4

Sumoylation of histone proteins is associated with

Accepted Answer

Transcription repression

Answer

Activation of gene transcription

Answer

Condensation of chromosome

Answer

DNA replication

Question 5

Which of the following statements about mitochondrial gene inheritance is true?

Accepted Answer

Mitochondrial genes are inherited from the mother.

Answer

Mitochondrial gene mutations are inherited in a paternal pattern.

Answer

Mitochondrial genes are inherited from the father.

Answer

Mitochondrial genes follow Mendelian inheritance.

Question 6

Which of the following statements about RNA capping is INCORRECT?

Accepted Answer

RNA capping occurs in the cytoplasm after transcription is complete.

Answer

RNA capping occurs in the nucleus and is co-transcriptional.

Answer

RNA capping involves the addition of a cap structure at the 5' end of the RNA molecule.

Answer

S-adenosyl methionine (SAM) acts as a methyl donor

Question 7

Which of the following is not a method for introducing a gene into target cells?

Accepted Answer

FISH

Answer

Electroporation

Answer

Transfection

Answer

Site directed recombination

Question 8

Which of the following statements is true regarding the role of enzymes in recombinant DNA technology?

Accepted Answer

DNA ligase is used

Answer

Acid phosphatase is used

Answer

Reverse transcriptase needed

Answer

Restriction endonucleases are involved

Question 9

Transition from G2 to M phase of the cell cycle is controlled by which?

Accepted Answer

Cyclin B

Answer

Retinoblastoma gene product

Answer

p53 protein

Answer

Cyclin E

Question 10

Gene amplification is achieved through

Accepted Answer

Polymerase Chain Reaction

Answer

DNA strand hybridization

Answer

In situ DNA hybridization

Answer

Ligase chain reaction (LCR)

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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