Tertiary and Quaternary Structures — MCQs
Most abundant collagen in the body is
Which of the following statements about protein denaturation is correct?
False regarding Alzheimer's disease (AD) is:
Abnormal accumulation of misfolded protein is seen in?
Size of fibrillary proteins in amyloidosis is:
Oxygen dissociation curve shifts to the right in:
Which of the following statements about chaperones is false?
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?
Which type of bond is primarily responsible for the primary structure of a protein?
Which of the following is a type of covalent bond?
Tertiary and Quaternary Structures Indian Medical PG Practice Questions and MCQs
Question 1: Most abundant collagen in the body is
- A. Type I (Correct Answer)
- B. Type II
- C. Type V
- D. Type VI
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.
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.
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.
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)
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.
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)
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.
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
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.
Question 6: Oxygen dissociation curve shifts to the right in:
- A. Hypothermia
- B. Hypercarbia (Correct Answer)
- C. Metabolic alkalosis
- D. Fetal hemoglobin (HbF) presence
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**.
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
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.
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.
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.
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
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.
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
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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