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1. General Principles & Basic Science MCQs

Practice Set 29 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 561

Topic: 1. General Principles & Basic Science

Which specific vector-related complication led to significant setbacks in early human gene therapy trials due to the activation of an oncogene?

. Adenovirus-induced systemic inflammatory response syndrome
. Retrovirus-induced insertional mutagenesis leading to leukemia
. AAV-mediated acute liver failure
. Plasmid-associated anaphylaxis

Correct Answer & Explanation

. Retrovirus-induced insertional mutagenesis leading to leukemia

Explanation

Early human trials utilizing retroviral vectors for severe combined immunodeficiency (X-SCID) resulted in insertional mutagenesis near oncogenes like LMO2. This led to the development of leukemia in some patients, highlighting integration risks.

Question 562

Topic: 1. General Principles & Basic Science

Which of the following viral vectors used in gene therapy integrates its genetic material into the host genome but is restricted to transducing only actively dividing cells?

. Retrovirus
. Adenovirus
. Adeno-associated virus
. Lentivirus
. Herpes simplex virus

Correct Answer & Explanation

. Lentivirus

Explanation

Retroviruses integrate their DNA into the host genome, allowing for stable, long-term expression, but they require the target cells to be actively dividing to gain access to the nucleus. Lentiviruses, a subclass of retroviruses, can infect both dividing and non-dividing cells.

Question 563

Topic: Biology, Genetics & Bone Healing

What is the primary advantage of utilizing an adeno-associated virus (AAV) over a standard adenovirus for gene delivery in orthopedic tissue engineering?

. Ability to hold larger DNA inserts up to 35 kb
. Lower immunogenicity and sustained gene expression
. Exclusive integration into host chromosomal DNA
. Ability to replicate without a helper virus
. Exclusive tropism for osteoblasts

Correct Answer & Explanation

. Lower immunogenicity and sustained gene expression

Explanation

AAV vectors provoke a very mild immune response compared to standard adenoviruses, allowing for more sustained gene expression in vivo. However, they have a limited packaging capacity (about 4.5 kb) and typically require a helper virus for replication.

Question 564

Topic: 1. General Principles & Basic Science
The CRISPR-Cas9 system has emerged as a powerful tool for genome editing in skeletal dysplasias. This system relies on which specific component to identify and bind the target DNA sequence?
. Restriction endonuclease
. Zinc finger domain
. Guide RNA (gRNA)
. Transcription activator-like effector
. Reverse transcriptase

Correct Answer & Explanation

. Guide RNA (gRNA)

Explanation

The CRISPR-Cas9 system uses a synthetic guide RNA (gRNA) that is complementary to the target DNA sequence. This gRNA directs the Cas9 nuclease to the specific genomic location to induce a double-strand break.

Question 565

Topic: 1. General Principles & Basic Science

To evaluate the efficacy of a novel therapeutic for osteoarthritis, a researcher quantifies the mRNA expression levels of Aggrecan in articular chondrocytes. Which technique is most appropriate for this purpose?

. Immunohistochemistry
. Southern blotting
. Flow cytometry
. Real-time Reverse Transcription PCR (RT-qPCR)
. Mass spectrometry

Correct Answer & Explanation

. Real-time Reverse Transcription PCR (RT-qPCR)

Explanation

RT-qPCR is the most sensitive and quantitative method for measuring specific mRNA expression levels in cells. It first converts RNA to complementary DNA (cDNA) using reverse transcriptase, then amplifies and quantifies it in real-time.

Question 566

Topic: Biology, Genetics & Bone Healing

Which of the following transcription factors is considered the master regulator essential for the differentiation of mesenchymal stem cells into the osteoblast lineage?

. Sox9
. PPAR-gamma
. Runx2 (Cbfa1)
. MyoD
. Osterix

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the master transcription factor required for osteoblast differentiation. Mice lacking Runx2 completely lack bone due to a maturation arrest of osteoblasts. Sox9 is the equivalent master regulator for chondrocytes.

Question 567

Topic: Biology, Genetics & Bone Healing

In the context of gene therapy for bone repair, which of the following accurately describes an 'ex vivo' gene delivery strategy?

. Direct injection of a viral vector into the fracture hematoma
. Harvesting host cells, transducing them with a vector in tissue culture, and reimplanting them
. Administering a systemic intravenous infusion of naked DNA
. Applying a collagen sponge soaked in recombinant BMP-2 directly to the defect
. Electroporation of host muscle tissue to induce local protein secretion

Correct Answer & Explanation

. Harvesting host cells, transducing them with a vector in tissue culture, and reimplanting them

Explanation

Ex vivo gene therapy involves isolating cells from the patient, modifying them genetically in a laboratory, and then implanting the transduced cells back into the patient. This allows for selection and quality control of the modified cells prior to implantation.

Question 568

Topic: Biology, Genetics & Bone Healing
The Wnt/β-catenin signaling pathway is a critical regulator of bone mass. Sclerostin (encoded by the SOST gene) inhibits bone formation by binding to and blocking which specific receptor complex?
. BMP Type I receptor
. Frizzled receptor
. TGF-beta receptor
. LRP5/6 coreceptor
. RANK ligand

Correct Answer & Explanation

. LRP5/6 coreceptor

Explanation

Sclerostin is a secreted glycoprotein that antagonizes Wnt signaling by binding to the LRP5/6 coreceptor on osteoblasts. This prevents the Wnt ligand from binding, leading to the degradation of β-catenin and a decrease in bone formation.

Question 569

Topic: 1. General Principles & Basic Science

What is the primary mechanism of action of small interfering RNA (siRNA) when used as a therapeutic tool in molecular orthopedics?

. Post-transcriptional gene silencing via mRNA degradation
. Direct inhibition of RNA polymerase II transcription
. Competitive binding to cell surface receptors
. Introduction of nonsense mutations into the host DNA
. Enhancement of ribosomal translation efficiency

Correct Answer & Explanation

. Post-transcriptional gene silencing via mRNA degradation

Explanation

siRNA mediates RNA interference (RNAi), a process that leads to specific post-transcriptional gene silencing. The siRNA binds to a complementary target mRNA sequence, leading to its cleavage and degradation by the RNA-induced silencing complex (RISC).

Question 570

Topic: Biology, Genetics & Bone Healing

A laboratory develops a viral vector that possesses an RNA genome, integrates stably into the host cell DNA, and is uniquely capable of infecting non-dividing cells such as mature neurons or resting osteocytes. Which vector fits this description?

. Adenovirus
. Simple retrovirus (e.g., Murine Leukemia Virus)
. Lentivirus
. Herpes simplex virus
. Adeno-associated virus

Correct Answer & Explanation

. Lentivirus

Explanation

Lentiviruses are a subclass of retroviruses with an RNA genome that reverse transcribes into DNA and integrates into the host genome. Unlike simple retroviruses, lentiviruses have the machinery to actively transport their pre-integration complex through the nuclear membrane of intact, non-dividing cells.

Question 571

Topic: Biology, Genetics & Bone Healing
Marfan syndrome is classically caused by a mutation in the FBN1 gene coding for fibrillin-1. The pathophysiology of this disorder is primarily related to the abnormal regulation and excessive signaling of which molecule?
. Fibroblast Growth Factor (FGF)
. Transforming Growth Factor-beta (TGF-β)
. Bone Morphogenetic Protein-2 (BMP-2)
. Insulin-like Growth Factor 1 (IGF-1)
. Vascular Endothelial Growth Factor (VEGF)

Correct Answer & Explanation

. Transforming Growth Factor-beta (TGF-β)

Explanation

Fibrillin-1 normally binds to and sequesters latent TGF-β in the extracellular matrix. Mutations in FBN1 lead to failed sequestration, resulting in excessive TGF-β signaling, which drives many of the phenotypic features of Marfan syndrome.

Question 572

Topic: 1. General Principles & Basic Science

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) gene. What is the primary molecular consequence of this defect in cartilage tissue?

. Failure to hydroxylate proline in type II collagen
. Defective cleavage of the N-terminal propeptide of collagen
. Defective intracellular sulfate transport leading to undersulfated proteoglycans
. Inability to assemble the collagen triple helix
. Constitutive activation of a tyrosine kinase receptor

Correct Answer & Explanation

. Defective intracellular sulfate transport leading to undersulfated proteoglycans

Explanation

The SLC26A2 gene encodes a sulfate transporter. Mutations cause defective intracellular transport of sulfate, leading to the undersulfation of proteoglycans in the cartilage matrix, which severely impairs cartilage structural integrity.

Question 573

Topic: 1. General Principles & Basic Science

During the polymerase chain reaction (PCR), what is the primary purpose of the initial heating phase, typically set between 94°C and 98°C?

. Denaturation of double-stranded DNA into single strands
. Annealing of specific oligonucleotide primers to the target sequence
. Optimal activation of the Taq polymerase enzyme
. Extension of the newly synthesized DNA strand
. Degradation of contaminating RNA molecules

Correct Answer & Explanation

. Denaturation of double-stranded DNA into single strands

Explanation

The high temperature (94-98°C) is used for the denaturation step in PCR. This breaks the hydrogen bonds holding the complementary DNA strands together, yielding single-stranded DNA required for primer binding in the subsequent annealing phase.

Question 574

Topic: Biology, Genetics & Bone Healing

A researcher conducts an assay to detect the presence of specific bone morphogenetic proteins (BMPs) in a tissue sample.

Based on standard molecular techniques, which method uses gel electrophoresis followed by antibody-based detection to confirm the presence and size of a specific protein?

. Northern blot
. Southern blot
. Microarray analysis
. Western blot
. In situ hybridization

Correct Answer & Explanation

. Western blot

Explanation

Western blotting is the standard technique for detecting specific proteins in a sample. It involves separating proteins by gel electrophoresis, transferring them to a membrane, and incubating with specific antibodies.

Question 575

Topic: 1. General Principles & Basic Science

The schematic illustrates a cellular process targeted in a novel orthopedic gene therapy.

When utilizing a non-viral plasmid vector for in vivo gene transfer as part of a bone healing strategy, what is the most characteristic outcome regarding gene expression?

. Permanent integration into the host genome with high risk of insertional mutagenesis
. Transient gene expression with a very low host immune response
. Sustained, lifelong gene expression due to episomal maintenance
. High transduction efficiency in non-dividing target cells
. Requirement of a helper virus for successful plasmid uncoating

Correct Answer & Explanation

. Transient gene expression with a very low host immune response

Explanation

Non-viral plasmid vectors are typically safer than viral vectors because they do not elicit a strong immune response and do not integrate into the host genome. However, their major limitation is low transfection efficiency and purely transient gene expression.

Question 576

Topic: 1. General Principles & Basic Science

Epigenetic regulation controls gene expression in bone and cartilage without altering the underlying DNA sequence. Which of the following modifications is most commonly associated with transcriptional silencing of a gene?

. Histone acetylation
. DNA demethylation
. DNA methylation at CpG islands
. Phosphorylation of RNA polymerase
. Alternative mRNA splicing

Correct Answer & Explanation

. DNA methylation at CpG islands

Explanation

DNA methylation, particularly at CpG islands within a gene's promoter region, generally leads to transcriptional repression or silencing. In contrast, histone acetylation is typically associated with open chromatin and active gene transcription.

Question 577

Topic: Biology, Genetics & Bone Healing

In the process of endochondral ossification, the sequential differentiation of mesenchymal cells into chondrocytes is heavily dependent on specific transcription factors. Which transcription factor is essential for this initial chondrogenic commitment?

. Runx2
. Sox9
. Osterix
. Twist
. Beta-catenin

Correct Answer & Explanation

. Sox9

Explanation

Sox9 is the critical master transcription factor that drives the differentiation of mesenchymal stem cells into chondrocytes. Without Sox9, mesenchymal condensation and cartilage formation during endochondral ossification cannot occur.

Question 578

Topic: Biology, Genetics & Bone Healing

Despite their high transduction efficiency and ability to produce high levels of therapeutic proteins like BMP-2, standard adenoviral vectors have a significant limitation that often precludes their systemic clinical use. What is this primary limitation?

. Inability to transduce non-dividing cells
. Extremely limited DNA packaging capacity (<2 kb)
. High risk of oncogenic insertional mutagenesis
. Elicitation of a severe host immune response
. Absolute requirement for host cell replication

Correct Answer & Explanation

. Elicitation of a severe host immune response

Explanation

Adenoviral vectors do not integrate into the host genome (reducing oncogenic risk) and can infect non-dividing cells. Their main clinical limitation is their high immunogenicity, which can elicit severe, sometimes fatal, inflammatory responses.

Question 579

Topic: 1. General Principles & Basic Science

Southern blotting is a foundational laboratory technique used primarily in basic orthopedic science to detect a specific sequence of which of the following macromolecules?

. DNA
. RNA
. Protein
. Lipids
. Carbohydrates

Correct Answer & Explanation

. DNA

Explanation

Southern blotting is used to detect specific DNA sequences in DNA samples. Northern blotting is used for RNA, and Western blotting is used to detect specific proteins.

Question 580

Topic: 1. General Principles & Basic Science

In molecular biology studies evaluating the upregulation of specific inflammatory markers in osteoarthritis, which technique is most appropriate for detecting specific mRNA sequences to quantify gene expression?

. Southern blot
. Northern blot
. Western blot
. Eastern blot
. Flow cytometry

Correct Answer & Explanation

. Northern blot

Explanation

Northern blotting detects specific RNA sequences (specifically mRNA) to study gene expression. It involves separating RNA fragments by size via electrophoresis and probing with a complementary sequence.

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