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Biology, Genetics & Bone Healing MCQs

Practice Set 5 of 212

This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 81

Topic: Biology, Genetics & Bone Healing

A researcher is evaluating the expression of BMP-2 protein levels in a harvested osteoblast culture following gene transduction. Which laboratory technique is most appropriate for quantifying specific protein levels?

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

Correct Answer & Explanation

. Western blot

Explanation

Western blotting is used to detect and quantify specific proteins in a sample using antibodies. Southern blotting detects DNA, while Northern blotting detects RNA.

Question 82

Topic: Biology, Genetics & Bone Healing

Lentiviruses are a subclass of retroviruses increasingly used in orthopedic gene therapy. What unique advantage do they offer over traditional retroviruses?

. They do not integrate into the host genome
. They are strictly non-immunogenic
. They can transduce both dividing and non-dividing cells
. They have a strict tropism for osteoblasts only

Correct Answer & Explanation

. They can transduce both dividing and non-dividing cells

Explanation

Unlike standard retroviruses which require cells to be actively dividing to enter the nucleus, lentiviruses can transport their genome into the nucleus of non-dividing cells. This broadens their applicability in tissues like cartilage.

Question 83

Topic: Biology, Genetics & Bone Healing

Gene therapy utilizing the delivery of the BMP-2 gene to muscle-derived stem cells has been shown to induce heterotopic ossification. What type of cellular process primarily characterizes this new bone formation?

. Endochondral ossification
. Intramembranous ossification
. Apoptosis
. Dedifferentiation

Correct Answer & Explanation

. Endochondral ossification

Explanation

Muscle-derived stem cells transduced with BMP-2 typically undergo a cartilage intermediate phase followed by osteogenesis. This process mimics endochondral ossification to form ectopic bone.

Question 84

Topic: Biology, Genetics & Bone Healing

When utilizing ex vivo gene therapy for delayed fracture healing, what is the most common and practical target cell harvested, genetically modified, and re-implanted?

. Erythrocytes
. Mesenchymal stem cells (MSCs)
. Mature osteocytes
. Polymorphonuclear leukocytes

Correct Answer & Explanation

. Mesenchymal stem cells (MSCs)

Explanation

Mesenchymal stem cells (MSCs) are ideal vehicles for ex vivo gene therapy in orthopedics. They are easily harvested from bone marrow, expandable in culture, and possess osteogenic potential.

Question 85

Topic: Biology, Genetics & Bone Healing

Which of the following growth factors, commonly targeted in fracture healing gene therapy, functions as a powerful factor primarily stimulating the formation of new blood vessels?

. BMP-7
. TGF-beta 1
. VEGF
. IGF-1

Correct Answer & Explanation

. VEGF

Explanation

Vascular Endothelial Growth Factor (VEGF) is a primary driver of angiogenesis. This is a critical step in the early phases of fracture healing and endochondral ossification.

Question 86

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 87

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 88

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 89

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 90

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 91

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 92

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 93

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 94

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 95

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 96

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 97

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 98

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 99

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 100

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.

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