Protein folding and chaperones US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Protein folding and chaperones. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Protein folding and chaperones US Medical PG Question 1: A 32-year-old woman is brought to your office by her husband. The husband says that she had been acting strange lately. She has been forgetful, and she sometimes becomes angered for no reason, which is highly unusual for her. She has also been having random, uncontrollable movements, which are also new. On examination, she appears withdrawn and flat. On further questioning, she reveals that her father died at age 45 from a movement disorder. Which of the following is the pathological hallmark of the patient's condition?
- A. Lipohyalinosis
- B. Loss of neurons in the caudate nucleus and putamen (Correct Answer)
- C. Substantia nigra pars compacta
- D. Alpha-synuclein intracellular inclusions
- E. Beta-amyloid plaques
Protein folding and chaperones Explanation: ***Loss of neurons in the caudate nucleus and putamen***
- The patient's symptoms (forgetfulness, anger, uncontrolled movements) and family history of an early-onset movement disorder (father died at age 45) are highly suggestive of **Huntington's disease**.
- **Huntington's disease** is characterized pathologically by **selective atrophy and loss of GABAergic neurons** in the **caudate nucleus and putamen** within the basal ganglia.
*Lipohyalinosis*
- **Lipohyalinosis** refers to the **thickening of the vessel walls** of small penetrating arteries, often seen in the brain, and is associated with **lacunar infarcts** due to hypertension and diabetes.
- While it can lead to neurological symptoms, it does not explain the specific combination of psychiatric, cognitive, and choreiform movements with an autosomal dominant family history.
*Substantia nigra pars compacta*
- Degeneration of the **substantia nigra pars compacta** and the resultant **loss of dopaminergic neurons** is the hallmark of **Parkinson's disease**.
- Parkinson's disease typically presents with tremor, rigidity, bradykinesia, and postural instability, which are different from the patient's choreiform movements.
*Alpha-synuclein intracellular inclusions*
- **Alpha-synuclein intracellular inclusions**, known as **Lewy bodies**, are the characteristic pathological finding in **Parkinson's disease** and **Lewy body dementia**.
- These are not associated with Huntington's disease, and the clinical presentation of the patient is not typical of either Parkinson's or Lewy body dementia.
*Beta-amyloid plaques*
- **Beta-amyloid plaques** are extracellular protein deposits, along with **neurofibrillary tangles** (tau protein), that are the pathological hallmarks of **Alzheimer's disease**.
- While Alzheimer's involves cognitive decline, it does not typically present with the prominent choreiform movements and specific genetic inheritance pattern seen in this patient.
Protein folding and chaperones US Medical PG Question 2: Which factor most strongly influences protein filtration at the glomerulus?
- A. Electrical charge
- B. Molecular size (Correct Answer)
- C. Shape
- D. Temperature
Protein folding and chaperones Explanation: ***Molecular size***
- The glomerular filtration barrier, particularly the **slit diaphragms** between podocytes, acts as a size-selective filter, restricting the passage of larger molecules.
- Proteins like **albumin** (molecular radius ~36 Å, molecular weight ~69 kDa) are significantly large, making them difficult to pass through the filtration barrier.
- Size selectivity is the **primary and most important** factor in protein filtration.
*Electrical charge*
- The glomerular basement membrane contains **negatively charged proteoglycans** (heparan sulfate), which repel negatively charged proteins like albumin, contributing to their retention.
- While important, the role of electrical charge is **secondary** to molecular size in preventing the bulk passage of most proteins.
*Shape*
- While abnormal protein shapes (e.g., **amyloid fibrils**) can impact filtration in specific disease states, the typical physiological filtration of most proteins is primarily governed by size and charge.
- The inherent shape of normal globular proteins plays a less direct role compared to their overall size.
*Temperature*
- **Physiological temperature** is relatively constant in the body and does not directly influence the molecular interactions and physical properties of the glomerular filtration barrier in a way that significantly alters protein filtration.
- Temperature changes would lead to denaturation or aggregation, which are not the primary determinants of normal protein filtration.
Protein folding and chaperones US Medical PG Question 3: A 73-year-old man presents to his primary care doctor with his son who reports that his father has been acting strangely. He has started staring into space throughout the day and has a limited attention span. He has been found talking to people who are not present and has gotten lost while driving twice. He has occasional urinary incontinence. His past medical history is notable for a stroke 5 years ago with residual right arm weakness, diabetes, hypertension, and hyperlipidemia. He takes aspirin, glyburide, metformin, lisinopril, hydrochlorothiazide, and atorvastatin. On examination, he is oriented to person and place but thinks the year is 1989. He is inattentive throughout the exam. He takes short steps while walking. His movements are grossly slowed. A brain biopsy in this patient would most likely reveal which of the following?
- A. Large intracellular vacuoles within a spongiform cortex
- B. Intracellular round aggregates of hyperphosphorylated microtubule-associated protein
- C. Marked diffuse cortical atherosclerosis
- D. Eosinophilic intracytoplasmic inclusions (Correct Answer)
- E. Extracellular amyloid plaques
Protein folding and chaperones Explanation: **Eosinophilic intracytoplasmic inclusions**
* The constellation of **fluctuating cognitive impairment**, **visual hallucinations** (talking to people not present), and **parkinsonian features** (slowed movements, short steps) are highly characteristic of **dementia with Lewy bodies (DLB)**.
* Brain biopsies in DLB reveal **Lewy bodies**, which are **eosinophilic intracytoplasmic aggregates of alpha-synuclein**.
*Large intracellular vacuoles within a spongiform cortex*
* This description is characteristic of **spongiform encephalopathy**, such as **Creutzfeldt-Jakob disease**.
* CJD presents with rapidly progressive dementia, myoclonus, and ataxia, which are not the primary features in this patient.
*Intracellular round aggregates of hyperphosphorylated microtubule-associated protein*
* This describes **neurofibrillary tangles**, primarily composed of **hyperphosphorylated tau protein**, which are a hallmark of **Alzheimer's disease**.
* While Alzheimer's involves memory loss and cognitive decline, the prominent visual hallucinations and parkinsonism are more suggestive of DLB.
*Marked diffuse cortical atherosclerosis*
* While the patient has a history of stroke and vascular risk factors, **diffuse cortical atherosclerosis** is a pathological finding associated with **vascular dementia**.
* Vascular dementia typically presents with a stepwise decline in cognitive function and focal neurological deficits, but the prominent hallucinations and parkinsonism point away from a primary diagnosis of vascular dementia alone.
*Extracellular amyloid plaques*
* These are **beta-amyloid plaques**, another key pathological feature of **Alzheimer's disease**.
* While patients with DLB can sometimes have co-existing Alzheimer's pathology, the primary and most defining characteristic of DLB are the Lewy bodies.
Protein folding and chaperones US Medical PG Question 4: An epidemiologist is evaluating the efficacy of Noxbinle in preventing HCC deaths at the population level. A clinical trial shows that over 5 years, the mortality rate from HCC was 25% in the control group and 15% in patients treated with Noxbinle 100 mg daily. Based on this data, how many patients need to be treated with Noxbinle 100 mg to prevent, on average, one death from HCC?
- A. 20
- B. 73
- C. 10 (Correct Answer)
- D. 50
- E. 100
Protein folding and chaperones Explanation: ***10***
- The **number needed to treat (NNT)** is calculated by first finding the **absolute risk reduction (ARR)**.
- **ARR** = Risk in control group - Risk in treatment group = 25% - 15% = **10%** (or 0.10).
- **NNT = 1 / ARR** = 1 / 0.10 = **10 patients**.
- This means that **10 patients must be treated with Noxbinle to prevent one death from HCC** over 5 years.
*20*
- This would result from an ARR of 5% (1/0.05 = 20), which is not supported by the data.
- May arise from miscalculating the risk difference or incorrectly halving the actual ARR.
*73*
- This value does not correspond to any standard calculation of NNT from the given mortality rates.
- May result from confusion with other epidemiological measures or calculation error.
*50*
- This would correspond to an ARR of 2% (1/0.02 = 50), which significantly underestimates the actual risk reduction.
- Could result from incorrectly calculating the difference as a proportion rather than absolute percentage points.
*100*
- This would correspond to an ARR of 1% (1/0.01 = 100), grossly underestimating the treatment benefit.
- May result from confusing ARR with relative risk reduction or other calculation errors.
Protein folding and chaperones US Medical PG Question 5: A 9-year-old boy is brought to his primary care physician after his mom noticed that he was limping. He says that he has been experiencing significant hip and knee pain over the last 2 months but thought he may have just strained a muscle. Radiographs show a collapse of the femoral head, and he is diagnosed with Legg-Calve-Perthes disease. He undergoes surgery and is placed in a Petrie cast from his hips to his toes bilaterally so that he is unable to move his knees or ankles. Eight weeks later, the cast is removed, and he is found to have significantly smaller calves than before the cast was placed. Which process in myocytes is most likely responsible for this finding?
- A. Decreased formation of double membrane bound vesicles
- B. Increased formation of double membrane bound vesicles
- C. Monoubiquitination of proteins
- D. Inhibition of gene transcription
- E. Polyubiquitination of proteins (Correct Answer)
Protein folding and chaperones Explanation: ***Polyubiquitination of proteins***
- **Polyubiquitination** targets proteins for degradation by the **proteasome**, a key mechanism in skeletal muscle atrophy due to disuse.
- The cast-induced disuse leads to muscle fiber shrinkage, as the cellular machinery for protein breakdown becomes more active than protein synthesis.
*Decreased formation of double membrane bound vesicles*
- This option refers to a decrease in **autophagy**, a process where cells degrade and recycle cellular components. While autophagy is involved in muscle atrophy, a *decrease* in this process would generally lead to accumulation of cellular components rather than a reduction in muscle mass.
- Autophagy would typically be *increased* during disuse atrophy to break down unnecessary components, not decreased.
*Increased formation of double membrane bound vesicles*
- This describes **increased autophagy**, a process that contributes to muscle atrophy by degrading cell components, including organelles and proteins. However, the primary and most direct mechanism for the rapid degradation of muscle proteins in disuse atrophy is the ubiquitin-proteasome pathway, rather than autophagy in this specific context.
- While autophagy does play a role in muscle wasting, **ubiquitin-proteasome system** is considered the dominant pathway for targeted protein degradation in disuse atrophy.
*Monoubiquitination of proteins*
- **Monoubiquitination** is typically involved in regulatory processes like **endomembrane trafficking**, **DNA repair**, and changing protein activity or localization, not directly in targeting proteins for proteasomal degradation.
- Unlike polyubiquitination, which marks proteins for destruction, monoubiquitination typically serves as a regulatory signal for various cellular functions without leading to rapid protein breakdown.
*Inhibition of gene transcription*
- While prolonged disuse can lead to changes in gene expression, including the downregulation of genes involved in muscle growth, the immediate and direct cause of muscle mass reduction in the context of acute disuse is the **accelerated degradation of existing proteins**.
- **Reduced gene transcription** would reduce the *synthesis* of new proteins, but the significant and rapid atrophy observed also requires the active breakdown of existing muscle proteins.
Protein folding and chaperones US Medical PG Question 6: A 67-year-old man comes to the physician for a follow-up examination after he was diagnosed with mantle cell lymphoma. The physician recommends a chemotherapeutic regimen containing bortezomib. Which of the following best describes the effect of this drug?
- A. Crosslinking of purine bases
- B. Preventing the relaxation of DNA supercoils
- C. Inhibition of tyrosine kinase receptors
- D. Accumulation of ubiquitinated proteins (Correct Answer)
- E. Stabilization of tubulin polymers
Protein folding and chaperones Explanation: ***Accumulation of ubiquitinated proteins***
- **Bortezomib** is a **proteasome inhibitor**, specifically targeting the 26S proteasome, which is responsible for degrading ubiquitinated proteins.
- Its inhibition leads to the accumulation of various **ubiquitinated proteins**, including pro-apoptotic factors, ultimately inducing **apoptosis** in cancer cells.
*Crosslinking of purine bases*
- This mechanism is characteristic of **alkylating agents** such as cyclophosphamide or cisplatin, which form covalent bonds with DNA, preventing replication and transcription.
- **Bortezomib** does not directly crosslink DNA bases; its primary action is on protein degradation pathways.
*Preventing the relaxation of DNA supercoils*
- This describes the mechanism of **topoisomerase inhibitors**, such as etoposide (topoisomerase II) or irinotecan (topoisomerase I), which block DNA replication and repair.
- Bortezomib has a distinct mechanism involving proteasome inhibition, not direct interaction with DNA or topoisomerases.
*Inhibition of tyrosine kinase receptors*
- This is the action of **tyrosine kinase inhibitors**, a class of drugs like imatinib or gefitinib, that target specific signaling pathways involved in cell growth and proliferation.
- Bortezomib's anti-cancer effects are mediated through protein degradation pathways, not by inhibiting receptor tyrosine kinases.
*Stabilization of tubulin polymers*
- This mechanism is characteristic of **taxanes** (e.g., paclitaxel), which hyperstabilize microtubules, interfering with cell division.
- **Bortezomib** does not affect microtubule dynamics; its action is focused on the proteasomal degradation system.
Protein folding and chaperones US Medical PG Question 7: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?
- A. "Does the diarrhea typically precede the constipation, or vice-versa?"
- B. "Is the diarrhea foul-smelling?"
- C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
- D. "Are the symptoms worse in the morning or at night?"
- E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)
Protein folding and chaperones Explanation: ***Can you tell me more about the symptoms you have been experiencing?***
- This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis.
- In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions.
*Does the diarrhea typically precede the constipation, or vice-versa?*
- While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience.
- It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture.
*Is the diarrhea foul-smelling?*
- Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions.
- However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed.
*Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life*
- Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time.
- However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially.
*Are the symptoms worse in the morning or at night?*
- Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related.
- This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.
Protein folding and chaperones US Medical PG Question 8: A group of scientists is studying the mechanism by which the human papillomavirus (HPV) vaccine confers immunity. They observe that during inoculation of test subjects, certain viral proteins are taken up by the organism's antigen-presenting cells (APCs) and presented on major histocompatibility complex (MHC) class I molecules. Which of the following is the correct term for the process that the scientists are observing in this inoculation?
- A. Priming of CD4+ T cells
- B. Ubiquitination
- C. Endogenous antigen presentation
- D. Cross-presentation (Correct Answer)
- E. Adhesion
Protein folding and chaperones Explanation: ***Cross-presentation***
- **Cross-presentation** occurs when an **antigen-presenting cell (APC)**, typically a dendritic cell, takes up **exogenous antigens** (like viral proteins from a vaccine) and presents them on **MHC class I molecules** to activate **CD8+ T cells**.
- This process is crucial for generating a strong **cytotoxic T lymphocyte (CTL) response** against viruses and tumors when the pathogen does not directly infect the APC.
*Priming of CD4+ T cells*
- **Priming of CD4+ T cells** involves the presentation of antigens on **MHC class II molecules**, which are typically loaded with **exogenous antigens** that have been internalized by the APC.
- The scenario describes antigen presentation on **MHC class I**, which points towards activation of CD8+ T cells, not CD4+ T cells directly.
*Ubiquitination*
- **Ubiquitination** is a process where the protein **ubiquitin** is attached to another protein, often marking it for degradation by the **proteasome**.
- While ubiquitination is involved in preparing **endogenous antigens** for MHC class I presentation, it is a *step within* the broader antigen processing pathway, not the overall process of an APC presenting exogenous antigen on MHC class I.
*Endogenous antigen presentation*
- **Endogenous antigen presentation** refers to the presentation of **peptides derived from proteins synthesized within the cell** (e.g., viral proteins in an infected cell) on **MHC class I molecules**.
- In this scenario, the viral proteins are *inoculated* into the organism, meaning they are initially **exogenous** to the APC before uptake, making cross-presentation the more accurate description.
*Adhesion*
- **Adhesion** refers to the process by which cells attach to other cells or to the extracellular matrix, often mediated by **adhesion molecules**.
- While cell-cell interactions are important in immune responses, "adhesion" does not describe the specific mechanism of an APC taking up an antigen and presenting it on MHC class I.
Protein folding and chaperones US Medical PG Question 9: An investigator is studying the function of the endoplasmic reticulum in genetically modified lymphocytes. A gene is removed that facilitates the binding of ribosomes to the endoplasmic reticulum. Which of the following processes is most likely to be impaired as a result of this genetic modification?
- A. Production of secretory proteins (Correct Answer)
- B. Neutralization of toxins
- C. Ubiquitination of proteins
- D. α-Oxidation of fatty acids
- E. Synthesis of ketone bodies
Protein folding and chaperones Explanation: ***Production of secretory proteins***
- Ribosomes bound to the **rough endoplasmic reticulum (RER)** are responsible for synthesizing proteins destined for secretion, insertion into membranes, or delivery to organelles like lysosomes.
- If ribosomes cannot bind to the ER, these proteins will be synthesized in the **cytosol** and lack the proper signals and processing for their intended destination and function.
*Neutralization of toxins*
- The **smooth endoplasmic reticulum (SER)**, not the RER, is primarily involved in **detoxification** processes, particularly drug metabolism and neutralization of toxins.
- This function relies on enzymes embedded within the SER membrane and is largely independent of ribosome binding.
*Ubiquitination of proteins*
- **Ubiquitination** is a post-translational modification that tags proteins for degradation by the **proteasome** or for trafficking to specific cellular compartments.
- This process occurs primarily in the **cytosol** and does not directly rely on ribosome binding to the ER for protein synthesis.
*α-Oxidation of fatty acids*
- **α-oxidation of fatty acids** is a metabolic pathway that occurs primarily in the **peroxisomes**.
- It is distinct from protein synthesis on the ER and would not be directly impacted by the inability of ribosomes to bind to the ER.
*Synthesis of ketone bodies*
- The **synthesis of ketone bodies** (ketogenesis) primarily occurs in the **mitochondria** of liver cells.
- This metabolic pathway is not directly dependent on ribosome binding to the endoplasmic reticulum for its function.
Protein folding and chaperones US Medical PG Question 10: An investigator is studying the genotypes of wingless fruit flies using full exome sequencing. Compared to wild-type winged fruit flies, the wingless fruit flies are found to have a point mutation in the gene encoding wing bud formation during embryogenesis. The point mutation in the gene causes the mRNA transcript to have a 'UUG' segment instead of an 'AUG' segment. Which of the following processes is most likely affected by this mutation?
- A. Cleavage of 5' intron
- B. Binding of met-tRNA to 40S complex (Correct Answer)
- C. Catalyzation of peptide bond formation
- D. Dissociation of mRNA from ribosome complex
- E. Shift of peptidyl-tRNA from A to P site
Protein folding and chaperones Explanation: ***Binding of met-tRNA to 40S complex***
- The **start codon AUG** is essential for the initiation of translation, as it signals where the ribosome should begin synthesizing the polypeptide chain and recruits the initiator tRNA carrying **methionine (met-tRNA)** to the 40S ribosomal subunit.
- A mutation from **AUG to UUG** means the ribosome will not recognize the correct start site, preventing the initial binding of met-tRNA and the formation of the **initiation complex**.
*Cleavage of 5' intron*
- This process is part of **RNA splicing**, which occurs after transcription in the nucleus, where introns are removed from the **pre-mRNA**.
- The described mutation affects a **codon sequence** in the mRNA, which is a post-splicing event related to translation, not intron cleavage.
*Catalyzation of peptide bond formation*
- This occurs during the **elongation phase of translation**, where the peptidyl transferase activity of the ribosome forms peptide bonds between amino acids.
- The mutation prevents the **initiation of translation** altogether, meaning elongation and peptide bond formation will not even begin.
*Dissociation of mRNA from ribosome complex*
- This event happens at the **termination phase of translation**, when a stop codon is reached, and release factors cause the ribosome to dissociate from the mRNA and the newly synthesized polypeptide.
- The mutation prevents the **start of translation**, so the ribosome will not reach the stage where it would dissociate from the mRNA.
*Shift of peptidyl-tRNA from A to P site*
- This is a step in the **elongation phase of translation**, specifically the **translocation process**, where the ribosome moves along the mRNA, shifting the peptidyl-tRNA from the A (aminoacyl) site to the P (peptidyl) site.
- Since the **initiation of translation** is blocked by the mutated start codon, the ribosome cannot begin polypeptide synthesis, and thus, elongation steps like translocation cannot occur.
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