Tertiary and Quaternary Structures Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Tertiary and Quaternary Structures. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Tertiary and Quaternary Structures Indian Medical PG Question 1: Most abundant collagen in the body is
- A. Type I (Correct Answer)
- B. Type II
- C. Type V
- D. Type VI
Tertiary and Quaternary Structures Explanation: ***Type I***
- **Type I collagen** is the most abundant type in the human body, constituting about 90% of the body's total collagen.
- It is primarily found in **skin, tendons, ligaments, bone, dentin, and intervertebral discs**, providing mechanical strength and structural integrity.
*Type II*
- **Type II collagen** is the main collagen found in **cartilage**, especially hyaline and elastic cartilage.
- It provides resistance to pressure and is crucial for the structure of the **intervertebral disc nucleus pulposus** and the **vitreous humor of the eye**.
*Type V*
- **Type V collagen** is a minor fibrillar collagen that associates with **type I collagen** to regulate fibril diameter and organization.
- It is found in **cornea, bone, and interstitial matrices**, playing a role in tissue development and integrity.
*Type VI*
- **Type VI collagen** is a microfibrillar collagen that forms bead-like microfibrils and is found in most **interstitial tissues**.
- It plays a significant role in anchoring other extracellular matrix components and is particularly abundant in the **basement membranes** of blood vessels and muscles.
Tertiary and Quaternary Structures Indian Medical PG Question 2: Which of the following statements about protein denaturation is correct?
- A. Biological properties are retained after denaturation.
- B. Denaturation is always irreversible.
- C. The primary structure of the protein is unaffected. (Correct Answer)
- D. Denaturation never results in proteins becoming insoluble.
Tertiary and Quaternary Structures Explanation: ***The primary structure of the protein is unaffected.***
- Denaturation refers to the disruption of a protein's **secondary, tertiary, and quaternary structures**, while the **covalent peptide bonds** that form the primary structure remain intact.
- The sequence of amino acids, which defines the primary structure, is not typically altered by denaturing agents such as heat, pH changes, or chemicals.
*Biological properties are retained after denaturation.*
- Denaturation typically leads to the **loss of a protein's specific three-dimensional shape**, which is essential for its biological function.
- Therefore, the biological properties and **activity of the protein are usually lost** or significantly impaired upon denaturation.
*Denaturation is always irreversible.*
- While many cases of denaturation are irreversible (e.g., cooking an egg), some proteins can **renature** if the denaturing conditions are removed, restoring their original structure and function.
- This reversibility depends on the **severity and duration of the denaturing agent**, as well as the protein's inherent stability.
*Denaturation never results in proteins becoming insoluble.*
- Denaturation often exposes **hydrophobic regions** of a protein that were previously buried within its folded structure, leading to aggregation and **precipitation**, thereby making the protein insoluble.
- This insolubility is a common consequence of denaturation, particularly with significant structural disruption.
Tertiary and Quaternary Structures Indian Medical PG Question 3: False regarding Alzheimer's disease (AD) is:
- A. Number of neurofibrillary tangles is associated with the severity of dementia
- B. Number of senile (neuritic) plaques correlates (increases) with age
- C. Presence of tau protein suggest neurodegeneration
- D. Extracellular inclusion (lesion) can occur in the absence of intracellular inclusions to make pathological diagnosis of AD (Correct Answer)
Tertiary and Quaternary Structures Explanation: ***Extracellular inclusion (lesion) can occur in the absence of intracellular inclusions to make pathological diagnosis of AD***
- A definitive pathological diagnosis of **Alzheimer's disease** requires both the presence of **extracellular amyloid plaques** and **intracellular neurofibrillary tangles** [1].
- Neither inclusion type alone is sufficient for the diagnosis, as amyloid plaques can be found in non-demented elderly individuals [1].
*Number of neurofibrillary tangles is associated with the severity of dementia*
- The **density and distribution of neurofibrillary tangles** (NFTs) directly correlate with the severity of cognitive impairment and **dementia** in AD [1].
- Tangles are composed of hyperphosphorylated **tau protein** and disrupt neuronal function, leading to neurodegeneration [2].
*Number of senile (neuritic) plaques correlates (increases) with age*
- The accumulation of **senile (neuritic) plaques**, composed primarily of **beta-amyloid protein**, generally increases with age, even in cognitively normal individuals [1].
- While plaques are a hallmark of AD, their mere presence is not always diagnostic of clinical dementia [1].
*Presence of tau protein suggest neurodegeneration*
- The presence of **hyperphosphorylated tau protein**, especially when forming **neurofibrillary tangles**, is a strong indicator of **neurodegeneration** [2].
- **Tauopathy** is a key pathological feature in AD and other neurodegenerative diseases [1].
**References:**
[1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1292-1294.
[2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 721-722.
Tertiary and Quaternary Structures Indian Medical PG Question 4: Abnormal accumulation of misfolded protein is seen in?
- A. Nephritic syndrome
- B. Sickle cell anemia
- C. Megaloblastic anemia
- D. Creutzfeldt-Jakob disease (Correct Answer)
Tertiary and Quaternary Structures Explanation: ***Creutzfeldt-Jakob disease***
- This is a neurodegenerative disease characterized by the accumulation of **abnormally folded prion proteins (PrPSc)** in the brain, leading to spongiform encephalopathy [1].
- The misfolding of normal cellular prion protein (PrPC) into its infectious and pathogenic form is central to the disease's pathology [2].
*Nephritic syndrome*
- This syndrome is characterized by inflammation of the **glomeruli** in the kidneys, leading to hematuria, proteinuria, and hypertension.
- It involves immune complex deposition and inflammation, not primarily the accumulation of misfolded proteins.
*Sickle cell anemia*
- This is a **genetic blood disorder** caused by a mutation in the beta-globin gene, leading to abnormal **hemoglobin S**.
- While hemoglobin S can polymerize and deform red blood cells, it is not considered a disease of generalized misfolded protein accumulation in the same sense as prion diseases.
*Megaloblastic anemia*
- This condition is caused by impaired **DNA synthesis**, often due to **vitamin B12 or folate deficiency**, leading to large, immature red blood cells.
- The pathology involves defective cell division and maturation, not the accumulation of misfolded proteins.
**References:**
[1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1284-1286.
[2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 712-713.
Tertiary and Quaternary Structures Indian Medical PG Question 5: Size of fibrillary proteins in amyloidosis is:
- A. 0-5 nm
- B. 7.5-10 nm (Correct Answer)
- C. 12-17 nm
- D. 18-20 nm
Tertiary and Quaternary Structures Explanation: ***7.5-10 nm***
- Amyloid fibrils are characteristically **non-branching**, **insoluble protein fibrils** that range in diameter from **7.5 to 10 nm**.
- This specific size and morphology are crucial for their identification via **electron microscopy**, which is a key diagnostic tool for amyloidosis.
*0-5 nm*
- This range is generally too small for the characteristic amyloid fibrils and would likely represent **monomeric proteins** or very small aggregates.
- Fibrillary structures typically need to be larger to achieve the stable, ordered beta-pleated sheet conformation seen in amyloid.
*12-17 nm*
- This diameter is typically **too large** for classic amyloid fibrils, which are known for their consistent size.
- Fibrils in this range might suggest different types of protein aggregates or other pathological structures not characteristic of amyloid.
*18-20 nm*
- Fibrils of this diameter are significantly **larger than the typical amyloid fibrils** and would not be consistent with the ultrastructural definition of amyloid.
- This size might be indicative of bundled fibrils or other forms of protein deposits.
Tertiary and Quaternary Structures Indian Medical PG Question 6: Oxygen dissociation curve shifts to the right in:
- A. Hypothermia
- B. Hypercarbia (Correct Answer)
- C. Metabolic alkalosis
- D. Fetal hemoglobin (HbF) presence
Tertiary and Quaternary Structures Explanation: ***Hypercarbia***
- Increased arterial partial pressure of carbon dioxide (**PaCO2**) leads to a decrease in pH (*acidosis*), which **reduces hemoglobin's affinity for oxygen**.
- This reduced affinity facilitates oxygen release to the tissues, shifting the **oxygen dissociation curve to the right** (Bohr effect).
*Hypothermia*
- **Decreased body temperature** causes an increase in hemoglobin's affinity for oxygen, making it harder for oxygen to be released to tissues.
- This effect shifts the **oxygen dissociation curve to the left**.
*Fetal hemoglobin (HbF) presence*
- **Fetal hemoglobin (HbF)** has a higher affinity for oxygen compared to adult hemoglobin (HbA).
- This higher affinity helps in oxygen transfer from the mother to the fetus and shifts the **oxygen dissociation curve to the left**.
*Metabolic alkalosis*
- **Metabolic alkalosis** is characterized by an increase in blood pH, which enhances hemoglobin's affinity for oxygen.
- This increased affinity makes it more difficult for oxygen to be unloaded in the tissues and shifts the **oxygen dissociation curve to the left**.
Tertiary and Quaternary Structures Indian Medical PG Question 7: Which of the following statements about chaperones is false?
- A. Are lipid in nature (Correct Answer)
- B. Cause folding of proteins
- C. Include heat shock proteins
- D. May have ATPase activity
Tertiary and Quaternary Structures Explanation: ***Are lipid in nature***
- Chaperones are **proteins** (typically **heat shock proteins** or **chaperonins**), not lipids.
- Their function involves assisting in the proper **folding and assembly of other proteins**, and they are composed of amino acids.
*Cause folding of proteins*
- Chaperones **do not cause** proteins to fold; rather, they **assist in proper folding** and refolding by preventing aggregation or misfolding.
- They bind to nascent or partially unfolded proteins to guide them towards their correct three-dimensional structure.
*May have ATPase activity*
- Many chaperones, especially **Hsp70** and **chaperonins** like GroEL/GroES, utilize **ATP hydrolysis** for their function.
- This **ATPase activity** drives conformational changes essential for binding, release, and refolding of their client proteins.
*Include heat shock proteins*
- The **heat shock protein (Hsp)** families (e.g., Hsp70, Hsp90, Hsp60) are a major class of chaperones.
- Hsps are upregulated in response to stress (like heat) to help refold damaged proteins and prevent aggregation.
Tertiary and Quaternary Structures Indian Medical PG Question 8: A pregnant woman is able to transfer oxygen to her fetus because fetal hemoglobin has a greater affinity for oxygen than does adult hemoglobin. Why is the affinity of fetal hemoglobin for oxygen higher?
- A. There is less 2,3-BPG in the fetal circulation as compared to maternal circulation
- B. Fetal hemoglobin binds 2,3-BPG with fewer ionic bonds than the adult form. (Correct Answer)
- C. The tense form of hemoglobin is more prevalent in the circulation of the fetus
- D. The oxygen-binding curve of fetal hemoglobin is shifted to the right.
Tertiary and Quaternary Structures Explanation: ***Fetal hemoglobin binds 2,3-BPG with fewer ionic bonds than the adult form.***
* **Fetal hemoglobin (HbF)**, composed of two alpha and two gamma subunits, interacts less effectively with **2,3-bisphosphoglycerate (2,3-BPG)** due to a difference in its gamma subunits compared to the beta subunits of **adult hemoglobin (HbA)**.
* The reduced binding of 2,3-BPG to HbF stabilizes its **R (relaxed) state**, which has a higher oxygen affinity, facilitating oxygen transfer from the mother to the fetus.
*There is less 2,3-BPG in the fetal circulation as compared to maternal circulation*
* While 2,3-BPG plays a crucial role in regulating oxygen affinity, the primary reason for **fetal hemoglobin's higher oxygen affinity** is its inherent structural difference that leads to weaker binding of 2,3-BPG, not necessarily the concentration of 2,3-BPG in the fetal circulation.
* The **concentration of 2,3-BPG is typically similar or even slightly higher in fetal blood** to enhance oxygen unloading at the tissues, but its effect on HbF is diminished.
*The tense form of hemoglobin is more prevalent in the circulation of the fetus*
* The **tense form (T-state)** of hemoglobin has a **lower affinity for oxygen**, and its prevalence would lead to reduced oxygen binding, which is contrary to the physiological need of the fetus to extract oxygen from the maternal blood.
* **Fetal hemoglobin's higher oxygen affinity** means it spends more time in the **relaxed form (R-state)**, which is responsible for tighter oxygen binding.
*The oxygen-binding curve of fetal hemoglobin is shifted to the right.*
* An **oxygen-binding curve shifted to the right** indicates a **decreased affinity for oxygen** and would facilitate oxygen unloading, not oxygen loading.
* For fetal hemoglobin to effectively extract oxygen from maternal blood, its **oxygen-binding curve must be shifted to the left**, signifying a higher oxygen affinity.
Tertiary and Quaternary Structures Indian Medical PG Question 9: Which type of bond is primarily responsible for the primary structure of a protein?
- A. Hydrogen bond
- B. Disulfide bond
- C. Peptide bond (Correct Answer)
- D. Electrostatic bond
Tertiary and Quaternary Structures Explanation: ***Peptide bond***
- The **primary structure** of a protein is defined by the unique linear sequence of **amino acids** linked together by **peptide bonds**.
- These are **amide bonds** formed between the carboxyl group of one amino acid and the amino group of another, with the elimination of water.
*Hydrogen bond*
- **Hydrogen bonds** are crucial for the **secondary structure** (e.g., alpha-helices and beta-sheets) and **tertiary/quaternary structures** of proteins, stabilizing their 3D folds.
- They involve interactions between polar atoms, not the direct linkage of amino acids in the primary sequence.
*Disulfide bond*
- **Disulfide bonds** are **covalent bonds** formed between the sulfur atoms of two **cysteine residues**, contributing to the **tertiary** and sometimes **quaternary structure** stability.
- They are not involved in forming the linear sequence of amino acids, which is the primary structure.
*Electrostatic bond*
- **Electrostatic bonds**, or **ionic bonds**, occur between oppositely charged amino acid side chains and are important for **tertiary** and **quaternary structure** stability.
- They do not form the backbone of the protein's primary sequence.
Tertiary and Quaternary Structures Indian Medical PG Question 10: Which of the following is a type of covalent bond?
- A. Hydrogen bond
- B. Disulfide bond (Correct Answer)
- C. Ionic bond
- D. Electrostatic bond
Tertiary and Quaternary Structures Explanation: ***Correct: Disulfide bond***
- A **disulfide bond** is formed by the oxidation of two **thiol** (sulfhydryl) groups, creating a strong **covalent bond** between two sulfur atoms.
- These bonds are crucial for stabilizing the **tertiary and quaternary structures of proteins**, contributing significantly to their overall shape and function.
*Incorrect: Hydrogen bond*
- A **hydrogen bond** is a **weak electrostatic attraction** between a hydrogen atom covalently bonded to a highly electronegative atom (like oxygen or nitrogen) and another electronegative atom.
- It is an **intermolecular force** or a weak intramolecular force, not a covalent bond that involves the sharing of electrons.
*Incorrect: Ionic bond*
- An **ionic bond** is formed by the **complete transfer of electrons** from one atom to another, resulting in the formation of oppositely charged ions that attract each other.
- This bond involves **electrostatic attraction** between ions, rather than the sharing of electrons characteristic of covalent bonds.
*Incorrect: Electrostatic bond*
- An **electrostatic bond** is a general term for the attractive force between oppositely charged particles, encompassing **ionic bonds** and other weaker interactions.
- This term describes the **nature of the attraction** rather than the specific type of chemical bond (like covalent, which involves electron sharing).
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