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1. General Principles & Basic Science MCQs

Practice Set 30 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 581

Topic: Biology, Genetics & Bone Healing

An orthopedic researcher is evaluating a new bone graft substitute and wants to quantify the production of Osteocalcin protein by osteoblasts in vitro. Which laboratory test should be utilized?

. Southern blot
. Northern blot
. Polymerase chain reaction (PCR)
. Western blot
. Microarray

Correct Answer & Explanation

. Western blot

Explanation

Western blotting is an analytical technique used to detect specific proteins in a sample of tissue homogenate or extract. It relies on the use of specific antibodies to identify the target protein.

Question 582

Topic: 1. General Principles & Basic Science

Which of the following viral vectors used in gene therapy is capable of permanently integrating into the host cell's genome but is historically limited by its ability to infect actively dividing cells only?

. Adeno-associated virus (AAV)
. Adenovirus
. Retrovirus
. Lentivirus
. Herpes simplex virus

Correct Answer & Explanation

. Lentivirus

Explanation

Standard retroviruses require target cells to be actively dividing for genome integration to occur. In contrast, lentiviruses (a subclass of retroviruses) can integrate into the genomes of non-dividing cells.

Question 583

Topic: 1. General Principles & Basic Science

Adeno-associated viruses (AAV) are frequently preferred over adenoviruses for orthopedic gene therapy applications. Which of the following best describes the primary advantage of AAV in this context?

. Larger packaging capacity
. Ability to deliver RNA exclusively
. Lower immunogenicity
. Strict integration into actively dividing cells
. Ability to independently replicate

Correct Answer & Explanation

. Lower immunogenicity

Explanation

AAVs are highly favored for in vivo gene therapy because they elicit a very low immune response and cause no known human diseases. Adenoviruses, conversely, can provoke severe and highly destructive cellular immune responses.

Question 584

Topic: Biology, Genetics & Bone Healing

Review the cell cycle model representing dividing osteoblasts:

During the standard eukaryotic cell cycle, in which phase does DNA replication primarily occur?

. G1 phase
. G2 phase
. S phase
. M phase
. G0 phase

Correct Answer & Explanation

. S phase

Explanation

The Synthesis (S) phase of the cell cycle is when DNA replication takes place, resulting in the duplication of the cell's genetic content prior to entering the G2 phase and eventually Mitosis (M phase).

Question 585

Topic: Biology, Genetics & Bone Healing

In an ex vivo gene therapy approach designed to accelerate the healing of critical-sized bone defects, which of the following best describes the core methodology?

. Direct injection of viral vectors into the fracture site
. Systemic intravenous administration of therapeutic plasmids
. Using a gene gun to shoot DNA particles directly into the bone
. Applying a BMP-soaked collagen sponge directly to the defect
. Harvesting host cells, genetically modifying them in vitro, and reimplanting them

Correct Answer & Explanation

. Harvesting host cells, genetically modifying them in vitro, and reimplanting them

Explanation

Ex vivo gene therapy involves isolating cells from a patient, cultivating and genetically modifying them in a laboratory setting, and then transplanting these optimized cells back into the patient.

Question 586

Topic: 1. General Principles & Basic Science

Polymerase chain reaction (PCR) involves repeated cycles of temperature changes to amplify DNA. What is the primary purpose of the initial high-temperature step (typically 94-98°C)?

. Primer annealing to target sequences
. DNA extension by Taq polymerase
. Degradation of RNA impurities
. Denaturation of double-stranded DNA
. Ligation of newly synthesized DNA fragments

Correct Answer & Explanation

. Denaturation of double-stranded DNA

Explanation

The high-temperature denaturation step separates the double-stranded DNA into single strands. This exposes the target sequences, allowing primers to bind during the subsequent annealing phase.

Question 587

Topic: 1. General Principles & Basic Science

A researcher is evaluating reverse transcription polymerase chain reaction (RT-PCR) to study gene expression:

Which enzyme is uniquely essential for synthesizing complementary DNA (cDNA) from a messenger RNA (mRNA) template?

. DNA polymerase I
. RNA polymerase II
. Helicase
. DNA ligase
. Reverse transcriptase

Correct Answer & Explanation

. Reverse transcriptase

Explanation

Reverse transcriptase is an RNA-dependent DNA polymerase. It is responsible for creating a complementary DNA (cDNA) strand from an RNA template, a critical step in RT-PCR and retroviral replication.

Question 588

Topic: 1. General Principles & Basic Science

Which of the following viral vectors is characterized by its high transduction efficiency and ability to infect both dividing and non-dividing cells, but primarily remains episomal, leading to transient gene expression?

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

Correct Answer & Explanation

. Adenovirus

Explanation

Adenoviruses do not integrate into the host genome but instead persist as episomes within the nucleus. This results in robust but transient expression of the transgene, alongside a strong host immune response.

Question 589

Topic: 1. General Principles & Basic Science

In the process of gene cloning and recombinant DNA technology, what is the primary and specific function of restriction endonucleases?

. To synthesize complementary RNA from a DNA template
. To cleave DNA at specific, highly recognizable nucleotide sequences
. To covalently join two separate DNA fragments together
. To protect newly formed bacterial DNA from methylation
. To translate mature mRNA into complex polypeptides

Correct Answer & Explanation

. To cleave DNA at specific, highly recognizable nucleotide sequences

Explanation

Restriction endonucleases act as molecular scissors, cutting double-stranded DNA at specific recognition sites. The resulting fragments can then be ligated into vectors during cloning.

Question 590

Topic: 1. General Principles & Basic Science

When designing a gene delivery protocol to target fully differentiated, non-dividing articular chondrocytes, what is the major advantage of using lentiviral vectors over classic retroviral vectors?

. They are strictly episomal and avoid insertional mutagenesis
. They carry double-stranded DNA rather than RNA
. They do not integrate into the host cell's genome at all
. They have the unique ability to infect and integrate into non-dividing cells
. They deliberately elicit a massive local immune response to stimulate healing

Correct Answer & Explanation

. They have the unique ability to infect and integrate into non-dividing cells

Explanation

Unlike standard retroviruses, which require host cell division (nuclear envelope breakdown) to access the genome, lentiviruses possess pre-integration complexes that can cross the intact nuclear membrane of non-dividing cells.

Question 591

Topic: 1. General Principles & Basic Science
The CRISPR/Cas9 system is a revolutionary tool for targeted genome editing in orthopedic genetic research. In this system, what specific component directs the Cas9 nuclease to the exact target DNA sequence?
. A customized structural protein motif
. A short, synthesized sequence of guide RNA (gRNA)
. A randomly integrated modified plasmid sequence
. A specific naturally occurring restriction enzyme
. A highly specialized DNA polymerase

Correct Answer & Explanation

. A short, synthesized sequence of guide RNA (gRNA)

Explanation

The CRISPR system relies on a guide RNA (gRNA) specifically designed to be complementary to the target DNA sequence. The gRNA binds to the Cas9 enzyme and guides it to the precise genomic location to create a double-strand break.

Question 592

Topic: 1. General Principles & Basic Science

Which of the following methods of non-viral gene delivery utilizes short, high-voltage electrical pulses to temporarily create pores in the cell membrane, allowing exogenous DNA to enter?

. Lipofection
. Microinjection
. Sonoporation
. Electroporation
. Gene gun

Correct Answer & Explanation

. Electroporation

Explanation

Electroporation uses an electrical field to increase the permeability of the cell membrane, introducing pores through which plasmids or other macromolecules can pass. It is highly efficient for in vitro cell transfection.

Question 593

Topic: Biology, Genetics & Bone Healing

The differential diagnosis of abuse in a child with a long bone fracture includes all of the following conditions except:

. Myelodysplasia
. C ongenital insensitivity to pain
. Rickets
. C opper deficiency
. Metaphyseal dysplasia

Correct Answer & Explanation

. Metaphyseal dysplasia

Explanation

All of the diagnoses except metaphyseal dysplasia place patients at increased risk of fracture, and therefore could be confused with nonaccidental injury.

Question 594

Topic: 1. General Principles & Basic Science

In a bowed tibia, the tensile stress during weightbearing is greatest at which point:

. The apex on the convex side
. The apex on the concave side
. The proximal joint surface
. The distal joint surface
. There is never a tensile stress on a tibia.

Correct Answer & Explanation

. The apex on the convex side

Explanation

The moment becomes tensile at the apex on the convex side of a tibial bow, in contrast to the normal compressive stress in a straight diaphysis. The moment is equal to load multiplied by distance from the axis of load.

Question 595

Topic: Biology, Genetics & Bone Healing

Which of the following medications has not been shown to increase the risk of osteopenia or osteoporosis:

. Glucocorticoids
. Antacids containing aluminum
. Phenytoin
. Phenobarbital
. Pamidronate

Correct Answer & Explanation

. Pamidronate

Explanation

Pamidronate, a bisphosphonate, increases bone density by inhibiting resorption. All of the medications listed as possible answers decrease bone density.

Question 596

Topic: 1. General Principles & Basic Science

Compared to viral vectors, the advantages of non-viral vectors for gene delivery include all of the following except:

. Safety
. Less immunogenicity
. More efficiency
. Easier production
. Special packaging cell line

Correct Answer & Explanation

. Safety

Explanation

Due to safety concerns, immunogenicity, and production issues associated with viral vectors, non-viral delivery systems were developed by complexing of genes (DNA) to various chemical formulations. This makes the DNA stable and increases its uptake. They include plasmids, peptides, cationic liposomes, DNA-ligand complexes (recognize specific cell-surface receptors, leading to receptor- mediated uptake), and gene gun (particles of gold coated with DNA, forced into the cells with high velocity bombardment). However, their efficiency is lower than viral vectors.

Question 597

Topic: Biology, Genetics & Bone Healing

A 6-year-old child presents with back pain. Radiographs reveal a 'vertebra plana' deformity.

Biopsy of the lesion is most likely to demonstrate which of the following histological features?

. Multinucleated giant cells with a fibrous stroma
. Coffee-bean shaped nuclei with Birbeck granules
. Small blue cells forming Homer-Wright rosettes
. Atypical chondrocytes with myxoid background
. Woven bone lined by prominent osteoblasts

Correct Answer & Explanation

. Coffee-bean shaped nuclei with Birbeck granules

Explanation

The clinical presentation of vertebra plana in a child is highly characteristic of Langerhans cell histiocytosis (eosinophilic granuloma). Histology shows Langerhans cells with coffee-bean nuclei, Birbeck granules on electron microscopy, and positive CD1a/S-100 staining.

Question 598

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy presents with multiple fractures, blue sclerae, and hearing loss. A defect in which of the following is the primary cause of his condition?

. Fibroblast growth factor receptor 3 (FGFR3)
. Type I collagen
. Type II collagen
. Cartilage oligomeric matrix protein (COMP)
. Runx2 transcription factor

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is primarily caused by mutations in the COL1A1 or COL1A2 genes, which encode the chains of Type I collagen.

Question 599

Topic: Biology, Genetics & Bone Healing

When evaluating a child for suspected non-accidental trauma, which of the following laboratory profiles best differentiates severe nutritional rickets from osteogenesis imperfecta (OI)?

. Elevated alkaline phosphatase
. Decreased serum calcium
. Elevated parathyroid hormone
. Abnormal type I collagen synthesis
. Decreased vitamin D3

Correct Answer & Explanation

. Abnormal type I collagen synthesis

Explanation

While both conditions can cause pediatric fractures, OI is caused by abnormal type I collagen. Rickets typically presents with elevated PTH and Alk Phos, along with low/normal calcium and low Vitamin D.

Question 600

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain, refusing to bear weight. His temperature is 38.6°C, ESR is 45 mm/hr, and WBC is 10,500/mm³. Radiographs are unremarkable. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis?
. < 5%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria for septic arthritis of the hip include non-weight-bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. This patient meets three criteria, which corresponds to a 93% predicted probability of septic arthritis.

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